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An ATCA survey of debris disks at 7 millimeters: We present ATCA continuum observations at a wavelength of 6.8 mm of five
debris disks: $\beta$ Pictoris, q$^1$ Eridani, HD 107146, HD 181327, and HD
95086. These observations provide the detection at the longest wavelengths
obtained to date for all these debris disks. By combining our 6.8 mm data with
previous detections at shorter sub-millimeter/millimeter wavelengths we measure
the long wavelength spectral index of these sources. We then use previous
estimates for the temperature of the emitting dust to derive the spectral index
of the dust emissivity. Under the assumption that all the detected flux comes
from dust only, we constrain the slope of the solid size distribution, assumed
to be a power-law. The values that we infer for the slope of the size
distribution range between about 3.36 and 3.50. We compare our findings with
the case of the Fomalhaut debris disk and use these results to test the
predictions of collisional cascades of planetesimal belts. | astro-ph_EP |
Refined stellar, orbital and planetary parameters of the eccentric
HAT-P-2 planetary system: We present refined parameters for the extrasolar planetary system HAT-P-2
(also known as HD 147506), based on new radial velocity and photometric data.
HAT-P-2b is a transiting extrasolar planet that exhibits an eccentric orbit. We
present a detailed analysis of the planetary and stellar parameters, yielding
consistent results for the mass and radius of the star, better constraints on
the orbital eccentricity, and refined planetary parameters. The improved
parameters for the host star are M_star = 1.36 +/- 0.04 M_sun and R_star = 1.64
+/- 0.08 R_sun, while the planet has a mass of M_p = 9.09 +/- 0.24 M_Jup and
radius of R_p = 1.16 +/- 0.08 R_Jup. The refined transit epoch and period for
the planet are E = 2,454,387.49375 +/- 0.00074 (BJD) and P = 5.6334729 +/-
0.0000061 (days), and the orbital eccentricity and argument of periastron are e
= 0.5171 +/- 0.0033 and omega = 185.22 +/- 0.95 degrees. These orbital elements
allow us to predict the timings of secondary eclipses with a reasonable
accuracy of ~15 minutes. We also discuss the effects of this significant
eccentricity including the characterization of the asymmetry in the transit
light curve. Simple formulae are presented for the above, and these, in turn,
can be used to constrain the orbital eccentricity using purely photometric
data. These will be particularly useful for very high precision, space-borne
observations of transiting planets. | astro-ph_EP |
Searching for the HR 8799 Debris Disk with HST/STIS: We present a new algorithm for space telescope high contrast imaging of
close-to-face-on planetary disks called Optimized Spatially Filtered (OSFi)
normalization. This algorithm is used on HR 8799 Hubble Space Telescope (HST)
coronagraphic archival data, showing an over-luminosity after reference star
point spread function (PSF) subtraction that may be from the inner disk and/or
planetesimal belt components of this system. The PSF-subtracted radial profiles
in two separate epochs from 2011 and 2012 are consistent with one another, and
self-subtraction shows no residual in both epochs. We explore a number of
possible false-positive scenarios that could explain this residual flux,
including telescope breathing, spectral differences between HR 8799 and the
reference star, imaging of the known warm inner disk component, OSFi algorithm
throughput and consistency with the standard spider normalization HST PSF
subtraction technique, and coronagraph misalignment from pointing accuracy. In
comparison to another similar STIS dataset, we find that the over-luminosity is
likely a result of telescope breathing and spectral difference between HR 8799
and the reference star. Thus, assuming a non-detection, we derive upper limits
on the HR 8799 dust belt mass in small grains. In this scenario, we find that
the flux of these micron-sized dust grains leaving the system due to radiation
pressure is small enough to be consistent with measurements of other debris
disk halos. | astro-ph_EP |
High precision Symplectic Integrators for the Solar System: Using a Newtonian model of the Solar System with all 8 planets, we perform
extensive tests on various symplectic integrators of high orders, searching for
the best splitting scheme for long term studies in the Solar System. These
comparisons are made in Jacobi and Heliocentric coordinates and the
implementation of the algorithms is fully detailed for practical use. We
conclude that high order integrators should be privileged, with a preference
for the new $(10,6,4)$ method of (Blanes et al., 2012) | astro-ph_EP |
Collision detection for N-body Kepler systems: In a Keplerian system, a large number of bodies orbit a central mass.
Accretion disks, protoplanetary disks, asteroid belts, and planetary rings are
examples. Simulations of these systems require algorithms that are
computationally efficient. The inclusion of collisions in the simulations is
challenging but important. We intend to calculate the time of collision of two
astronomical bodies in intersecting Kepler orbits as a function of the orbital
elements. The aim is to use the solution in an analytic propagator ($N$-body
simulation) that jumps from one collision event to the next. We outline an
algorithm that maintains a list of possible collision pairs ordered
chronologically. At each step (the soonest event on the list), only the
particles created in the collision can cause new collision possibilities. We
estimate the collision rate, the length of the list, and the average change in
this length at an event, and study the efficiency of the method used. We find
that the collision-time problem is equivalent to finding the grid point between
two parallel lines that is closest to the origin. The solution is based on the
continued fraction of the ratio of orbital periods. Due to the large jumps in
time, the algorithm can beat tree codes (octree and $k$-d tree codes can
efficiently detect collisions) for specific systems such as the Solar System
with $N<10^8$. However, the gravitational interactions between particles can
only be treated as gravitational scattering or as a secular perturbation, at
the cost of reducing the time-step or at the cost of accuracy. While
simulations of this size with high-fidelity propagators can already span vast
timescales, the high efficiency of the collision detection allows many runs
from one initial state or a large sample set, so that one can study statistics. | astro-ph_EP |
Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No
evidence for Temporal Variation of the Spin-Orbit Angle: We present 12 new transit light curves and 16 new out-of-transit radial
velocity measurements for the XO-3 system. By modelling our newly collected
measurements together with archival photometric and Doppler velocimetric data,
we confirmed the unusual configuration of the XO-3 system, which contains a
massive planet ($M_P=11.92^{+0.59}_{-0.63} M_J$) on a relatively eccentric
($e=0.2853^{+0.0027}_{-0.0026}$) and short-period ($3.19152 \pm 0.00145\,$day)
orbit around a massive star ($M_*=1.219^{+0.090}_{-0.095} M_{\odot}$).
Furthermore, we find no strong evidence for a temporal change of either $V\sin
i_{*}$ (and by extension, the stellar spin vector of XO-3), or the transit
profile (and thus orbital angular momentum vector of XO-3b). We conclude that
the discrepancy in previous Rossiter-McLaughlin measurements ($70.0^{\circ} \pm
15.0^{\circ}$ (Hebrard et al. 2008); $37.3^{\circ} \pm 3.7^{\circ}$ (Winn et
al. 2009); $37.3^{\circ} \pm 3.0^{\circ}$ (Hirano et al. 2011)) may have
stemmed from systematic noise sources. | astro-ph_EP |
Multiband Optical Observation of P/2010 A2 Dust Tail: An inner main-belt asteroid, P/2010 A2, was discovered on January 6th, 2010.
Based on its orbital elements, it is considered that the asteroid belongs to
the Flora collisional family, where S-type asteroids are common, whilst showing
a comet-like dust tail. Although analysis of images taken by the Hubble Space
Telescope and Rosetta spacecraft suggested that the dust tail resulted from a
recent head-on collision between asteroids (Jewitt et al. 2010; Snodgrass et
al. 2010), an alternative idea of ice sublimation was suggested based on the
morphological fitting of ground-based images (Moreno et al. 2010). Here, we
report a multiband observation of P/2010 A2 made on January 2010 with a 105 cm
telescope at the Ishigakijima Astronomical Observatory. Three broadband
filters, $g'$, $R_c$, and $I_c$, were employed for the observation. The unique
multiband data reveals that the reflectance spectrum of the P/2010 A2 dust tail
resembles that of an Sq-type asteroid or that of ordinary chondrites rather
than that of an S-type asteroid. Due to the large error of the measurement, the
reflectance spectrum also resembles the spectra of C-type asteroids, even
though C-type asteroids are uncommon in the Flora family. The reflectances
relative to the $g'$-band (470 nm) are 1.096$\pm$0.046 at the $R_c$-band (650
nm) and 1.131$\pm$0.061 at the $I_c$-band (800 nm). We hypothesize that the
parent body of P/2010 A2 was originally S-type but was then shattered upon
collision into scaterring fresh chondritic particles from the interior, thus
forming the dust tail. | astro-ph_EP |
Coupling thermal evolution of planets and hydrodynamic atmospheric
escape in MESA: The long-term evolution of hydrogen-dominated atmospheres of sub-Neptune-like
planets is mostly controlled by two factors: a slow dissipation of the
gravitational energy acquired at the formation (known as thermal evolution) and
atmospheric mass loss. Here, we use MESA to self-consistently couple the
thermal evolution model of lower atmospheres with a realistic hydrodynamical
atmospheric evaporation prescription. To outline the main features of such
coupling, we simulate planets with a range of core masses (5-20 Mearth) and
initial atmospheric mass fractions (0.5-30%), orbiting a solar-like star at 0.1
au. In addition to our computed evolutionary tracks, we also study the
stability of planetary atmospheres, showing that the atmospheres of light
planets can be completely removed within 1 Gyr, and that compact atmospheres
have a better survival rate. From a detailed comparison between our results and
the output of the previous-generation models, we show that coupling between
thermal evolution and atmospheric evaporation considerably affects the thermal
state of atmospheres for low-mass planets and, consequently, changes the
relationship between atmospheric mass fraction and planetary parameters. We,
therefore, conclude that self-consistent consideration of the thermal evolution
and atmospheric evaporation is of crucial importance for evolutionary modeling
and a better characterization of planetary atmospheres. From our simulations,
we derive an analytical expression between the planetary radius and atmospheric
mass fraction at different ages. In particular, we find that, for a given
observed planetary radius, the predicted atmospheric mass fraction changes as
age^0.11. | astro-ph_EP |
A Giant Planet Around a Metal-poor Star of Extragalactic Origin: Stars in their late stage of evolution, such as Horizontal Branch stars, are
still largely unexplored for planets. We report the detection of a planetary
companion around HIP 13044, a very metal-poor star on the red Horizontal
Branch, based on radial velocity observations with a high-resolution
spectrograph at the 2.2-m MPG/ESO telescope. The star's periodic radial
velocity variation of P=16.2 days caused by the planet can be distinguished
from the periods of the stellar activity indicators. The minimum mass of the
planet is 1.25 Jupiter masses and its orbital semi-major axis 0.116 AU. Because
HIP 13044 belongs to a group of stars that have been accreted from a disrupted
satellite galaxy of the Milky Way, the planet most likely has an extragalactic
origin. | astro-ph_EP |
Aqueous alteration on main belt primitive asteroids: results from
visible spectroscopy: This work focuses on the study of the aqueous alteration process which acted
in the main belt and produced hydrated minerals on the altered asteroids. The
aqueous alteration is particularly important for unraveling the processes
occurring during the earliest times of the Solar System history, as it can give
information both on the asteroids thermal evolution and on the localization of
water sources in the asteroid belt. We present new spectral observations in the
visible region of 80 asteroids belonging to the primitive classes C, G, F, B
and P. We combine the present observations with the visible spectra of
asteroids available in the literature for a total of 600 primitive main belt
asteroids. Our analysis shows that the aqueous alteration sequence starts from
the P-type objects, practically unaltered, and increases through the F, B, C,
and G asteroids. Around 50% of the observed C-type asteroids show absorption
features in the vis. range due to hydrated silicates, implying that more than
70% of them will have a 3 $\mu$m absorption band and thus hydrated minerals on
their surfaces. The process dominates in primitive asteroids located between
2.3 and 3.1 AU, that is at smaller heliocentric distances than previously
suggested. The aqueous alteration process dominates in the 50--240 km sized
primitive asteroids, while it is less effective for bodies smaller than 50 km.
No correlation is found between the aqueous alteration process and the
asteroids albedo or orbital elements. Comparing the $\sim$ 0.7 $\mu$m band
parameters of hydrated silicates and CM2 carbonaceous chondrites, we see that
the band center of meteorites is at longer wavelengths than that of asteroids.
This difference on center positions may be attributed to different minerals
abundances, and to the fact that CM2 available on Earth might not be
representative of the whole aqueous altered asteroids population. | astro-ph_EP |
Molecular Outgassing in Centaur 29P/Schwassmann-Wachmann 1 During Its
Exceptional 2021 Outburst: Coordinated Multi-Wavelength Observations Using
nFLASH at APEX and iSHELL at the NASA-IRTF: The extraordinary 2021 September-October outburst of Centaur
29P/Schwassmann-Wachmann 1 afforded an opportunity to test the composition of
primitive Kuiper disk material at high sensitivity. We conducted nearly
simultaneous multi-wavelength spectroscopic observations of
29P/Schwassmann-Wachmann 1 using iSHELL at the NASA Infrared Telescope Facility
and nFLASH at the Atacama Pathfinder EXperiment (APEX) on 2021 October 6, with
follow-up APEX/nFLASH observations on 2021 October 7 and 2022 April 3. This
coordinated campaign between near-infrared and radio wavelengths enabled us to
sample molecular emission from a wealth of coma molecules and to perform
measurements that cannot be accomplished with either wavelength alone. We
securely detected CO emission on all dates with both facilities, including
velocity-resolved spectra of the CO (J=2-1) transition with APEX/nFLASH and
multiple CO (v=1-0) rovibrational transitions with IRTF/iSHELL. We report
rotational temperatures, coma kinematics, and production rates for CO and
stringent (3-sigma) upper limits on abundance ratios relative to CO for CH4,
C2H6, CH3OH, H2CO, CS, and OCS. Our upper limits for CS/CO and OCS/CO represent
their first values in the literature for this Centaur. Upper limits for CH4,
C2H6, CH3OH, and H2CO are the most stringent reported to date, and are most
similar to values found in ultra CO-rich Oort cloud comet C/2016 R2
(PanSTARRS), which may have implications for how ices are preserved in cometary
nuclei. We demonstrate the superb synergy of coordinated radio and
near-infrared measurements, and advocate for future small body studies that
jointly leverage the capabilities of each wavelength. | astro-ph_EP |
Cooling-Induced Vortex Decay in Keplerian Disks: Vortices are readily produced by hydrodynamical instabilities, such as the
Rossby wave instability, in protoplanetary disks. However, large-scale
asymmetries indicative of dust-trapping vortices are uncommon in sub-millimeter
continuum observations. One possible explanation is that vortices have short
lifetimes. In this paper, we explore how radiative cooling can lead to vortex
decay. Elliptical vortices in Keplerian disks go through adiabatic heating and
cooling cycles. Radiative cooling modifies these cycles and generates
baroclinicity that changes the potential vorticity of the vortex. We show that
the net effect is typically a spin down, or decay, of the vortex for a
sub-adiabatic radial stratification. We perform a series of two-dimensional
shearing box simulations, varying the gas cooling (or relaxation) time, $t_{\rm
cool}$, and initial vortex strength. We measure the vortex decay half-life,
$t_{\rm half}$, and find that it can be roughly predicted by the timescale
ratio $t_{\rm cool}/t_{\rm turn}$, where $t_{\rm turn}$ is the vortex
turnaround time. Decay is slow in both the isothermal ($t_{\rm cool}\ll t_{\rm
turn}$) and adiabatic ($t_{\rm cool}\gg t_{\rm turn}$) limits; it is fastest
when $t_{\rm cool}\sim0.1\,t_{\rm turn}$, where $t_{\rm half}$ is as short as
$\sim300$ orbits. At tens of au where disk rings are typically found, $t_{\rm
turn}$ is likely much longer than $t_{\rm cool}$, potentially placing vortices
in the fast decay regime. | astro-ph_EP |
An analytic solution to measure the gas size in protoplanetary discs in
the viscous self-similar scenario: In order to understand which mechanism is responsible for accretion in
protoplanetary discs, a robust knowledge of the observed disc radius using gas
tracers such as $^{12}$CO and other CO isotopologues is pivotal. Indeed, the
two main theories proposed, viscous accretion and wind-driven accretion,
predict different time evolution for the disc radii. In this Letter, we present
an analytical solution for the evolution of the disc radii in viscously
evolving protoplanetary discs using $^{12}$CO as a tracer, under the assumption
that the $^{12}$CO radius is the radius where the surface density of the disc
is equal to the threshold for CO photo-dissociation. We discuss the properties
of the solution and the limits of its applicability as a simple numerical
prescription to evaluate the observed disc radii of populations of discs. Our
results suggest that, in addition to photo-dissociation, also freeze out plays
an important role in setting the disc size. We find an effective reduction of
the CO abundance by about two orders of magnitude at the location of CO
photo-dissociation, which however should not be interpreted as the bulk
abundance of CO in the disc. The use of our analytical solution will allow to
compute disc sizes for large quantities of models without using expensive
computational resources such as radiative transfer calculations. | astro-ph_EP |
Physical Characterization of Metal-rich Near-Earth Asteroids 6178 (1986
DA) and 2016 ED85: Metal-rich near-Earth asteroids (NEAs) represent a small fraction of the NEA
population that is mostly dominated by S- and C-type asteroids. Because of
this, their identification and study provide us with a unique opportunity to
learn more about the formation and evolution of this particular type of bodies,
as well as their relationship with meteorites found on Earth. We present
near-infrared (NIR) spectroscopic data of NEAs 6178 (1986 DA) and 2016 ED85. We
found that the spectral characteristics of these objects are consistent with
those of metal-rich asteroids, showing red slopes, convex shapes, and a weak
pyroxene absorption band at $\sim$0.93 $\mu$m. The compositional analysis
showed that they have a pyroxene chemistry of Fs$_{40.6\pm3.3}$Wo$_{8.9\pm1.1}$
and a mineral abundance of $\sim$15% pyroxene and 85% metal. We determined that
these objects were likely transported to the near-Earth space via the 5:2 mean
motion resonance with Jupiter. Asteroid spectra were compared with the spectra
of mesosiderites and bencubbinites. Differences in the NIR spectra and pyroxene
chemistry suggest that bencubbinites are not good meteorite analogs.
Mesosiderites were found to have a similar pyroxene chemistry and produced a
good spectral match when metal was added to the silicate component. We
estimated that the amounts of Fe, Ni, Co, and the platinum group metals present
in 1986 DA could exceed the reserves worldwide. | astro-ph_EP |
A dearth of small particles in the transiting material around the white
dwarf WD 1145+017: White dwarf WD 1145+017 is orbited by several clouds of dust, possibly
emanating from actively disintegrating bodies. These dust clouds reveal
themselves through deep, broad, and evolving transits in the star's light
curve. Here, we report two epochs of multi-wavelength photometric observations
of WD 1145+017, including several filters in the optical, K$_\mathrm{s}$ and
4.5 $\mu$m bands in 2016 and 2017. The observed transit depths are different at
these wavelengths. However, after correcting for excess dust emission at
K$_\mathrm{s}$ and 4.5 $\mu$m, we find the transit depths for the white dwarf
itself are the same at all wavelengths, at least to within the observational
uncertainties of $\sim$5%-10%. From this surprising result, and under the
assumption of low optical depth dust clouds, we conclude that there is a
deficit of small particles (with radii $s \lesssim$ 1.5 $\mu$m) in the
transiting material. We propose a model wherein only large particles can
survive the high equilibrium temperature environment corresponding to 4.5 hr
orbital periods around WD 1145+017, while small particles sublimate rapidly. In
addition, we evaluate dust models that are permitted by our measurements of
infrared emission. | astro-ph_EP |
Ks band secondary eclipses of WASP-19b and WASP-43b with the
Anglo-Australian Telescope: We report new Ks band secondary eclipse observations for the hot-Jupiters
WASP-19b and WASP-43b. Using the IRIS2 infrared camera on the Anglo-Australian
Telescope (AAT), we measured significant secondary eclipses for both planets,
with depths of 0.287 -0.020/+0.020% and 0.181 -0.027/+0.027% for WASP-19b and
WASP-43b respectively. We compare the observations to atmosphere models from
the VSTAR line-by-line radiative transfer code, and examine the effect of C/O
abundance, top layer haze, and metallicities on the observed spectra. We
performed a series of signal injection and recovery exercises on the observed
light curves to explore the detection thresholds of the AAT+IRIS2 facility. We
find that the optimal photometric precision is achieved for targets brighter
than Kmag = 9, for which eclipses as shallow as 0.05% are detectable at >5
sigma significance. | astro-ph_EP |
Asteroid thermal modeling in the presence of reflected sunlight with an
application to WISE/NEOWISE observational data: This study addresses thermal modeling of asteroids with a new derivation of
the Near Earth Asteroid Thermal (NEATM) model which correctly accounts for the
presence of reflected sunlight in short wave IR bands. Kirchhoff's law of
thermal radiation applies to this case and has important implications. New
insight is provided into the eta parameter in the NEATM model and it is
extended to thermal models besides NEATM. The role of surface material
properties on eta is examined using laboratory spectra of meteorites and other
asteroid compositional proxies; the common assumption that emissivity e = 0.9
in asteroid thermal models may not be justified and can lead to misestimating
physical parameters. In addition, indeterminacy in thermal modeling can limit
its ability to uniquely determine temperature and other physical properties. A
new curve fitting approach allows thermal modeling to be done independent of
visible band observational parameters such as the absolute magnitude H. These
new thermal modeling techniques are applied to observational data for selected
asteroids from the WISE/NEOWISE mission. The previous NEOWISE analysis assumes
Kirchhoff's law does not apply. It also deviates strongly from established
statistical practice and systematically underestimates the sampling error
inherent in observing potentially irregular asteroids from a finite sample of
observations. As a result, the new analysis finds asteroid diameter and other
physical properties that have large differences from published NEOWISE results,
with greatly increased error estimates. NEOWISE results have a claimed +/-10%
accuracy for diameter estimates, but this is unsupported. ABSTRACT CONTINUED IN
PDF... | astro-ph_EP |
Early formation of planetary building blocks inferred from Pb isotopic
ages of chondrules: The most abundant components of primitive meteorites (chondrites) are
millimeter-sized glassy spherical chondrules formed by transient melting events
in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual
chondrules, we show that primary production of chondrules in the early solar
system was restricted to the first million years after formation of the Sun and
that these existing chondrules were recycled for the remaining lifetime of the
protoplanetary disk. This is consistent with a primary chondrule formation
episode during the early high-mass accretion phase of the protoplanetary disk
that transitions into a longer period of chondrule reworking. An abundance of
chondrules at early times provides the precursor material required to drive the
efficient and rapid formation of planetary objects via chondrule accretion. | astro-ph_EP |
Kepler-91b: a planet at the end of its life. Planet and giant host star
properties via light-curve variations: The evolution of planetary systems is intimately linked to the evolution of
their host star. Our understanding of the whole planetary evolution process is
based on the large planet diversity observed so far. To date, only few tens of
planets have been discovered orbiting stars ascending the Red Giant Branch.
Although several theories have been proposed, the question of how planets die
remains open due to the small number statistics. In this work we study the
giant star Kepler-91 (KOI-2133) in order to determine the nature of a
transiting companion. This system was detected by the Kepler Space Telescope.
However, its planetary confirmation is needed. We confirm the planetary nature
of the object transiting the star Kepler-91 by deriving a mass of $
M_p=0.88^{+0.17}_{-0.33} ~M_{\rm Jup}$ and a planetary radius of
$R_p=1.384^{+0.011}_{-0.054} ~R_{\rm Jup}$. Asteroseismic analysis produces a
stellar radius of $R_{\star}=6.30\pm 0.16 ~R_{\odot}$ and a mass of
$M_{\star}=1.31\pm 0.10 ~ M_{\odot} $. We find that its eccentric orbit
($e=0.066^{+0.013}_{-0.017}$) is just $1.32^{+0.07}_{-0.22} ~ R_{\star}$ away
from the stellar atmosphere at the pericenter. Kepler-91b could be the previous
stage of the planet engulfment, recently detected for BD+48 740. Our
estimations show that Kepler-91b will be swallowed by its host star in less
than 55 Myr. Among the confirmed planets around giant stars, this is the
planetary-mass body closest to its host star. At pericenter passage, the star
subtends an angle of $48^{\circ}$, covering around 10% of the sky as seen from
the planet. The planetary atmosphere seems to be inflated probably due to the
high stellar irradiation. | astro-ph_EP |
The Habitable Zones of Pre-Main-Sequence Stars: We calculate the pre-main-sequence HZ for stars of spectral classes F to M.
The spatial distribution of liquid water and its change during the
pre-main-sequence phase of protoplanetary systems is important in understanding
how planets become habitable. Such worlds are interesting targets for future
missions because the coolest stars could provide habitable conditions for up to
2.5 billion years post-accretion. Moreover, for a given star type, planetary
systems are more easily resolved because of higher pre-main-sequence stellar
luminosities, resulting in larger planet to star separation for cool stars than
is the case for the traditional main-sequence (MS) habitable zone (HZ). We use
1D radiative-convective climate and stellar evolutionary models to calculate
pre-main-sequence HZ distances for F1 to M8 stellar types. We also show that
accreting planets that are later located in the traditional MS HZ orbiting
stars cooler than a K5 (including the full range of M-stars) receive stellar
fluxes that exceed the runaway greenhouse threshold, and thus may lose
substantial amounts of water initially delivered to them. We predict that
M-star planets need to initially accrete more water than Earth did or,
alternatively, have additional water delivered later during the long
pre-main-sequence phase to remain habitable. Our findings are also consistent
with recent claims that Venus lost its water during accretion. | astro-ph_EP |
Phase Diagram for the Methane-Ethane System and its Implications for
Titan's Lakes: On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in
the lakes and seas. In this study, we have combined laboratory work and
modeling to refine the methane-ethane binary phase diagram at low temperatures
and probe how the molecules interact at these conditions. We used visual
inspection for the liquidus and Raman spectroscopy for the solidus. Through
these methods we determined a eutectic point of 71.15$\pm$0.5 K at a
composition of 0.644$\pm$0.018 methane - 0.356$\pm$0.018 ethane mole fraction
from the liquidus data. Using the solidus data, we found a eutectic isotherm
temperature of 72.2 K with a standard deviation of 0.4 K. In addition to
mapping the binary system, we looked at the solid-solid transitions of pure
ethane and found that, when cooling, the transition of solid I-III occurred at
89.45$\pm$0.2 K. The warming sequence showed transitions of solid III-II
occurring at 89.85$\pm$0.2 K and solid II-I at 89.65$\pm$0.2 K. Ideal
predictions were compared to molecular dynamics simulations to reveal that the
methane-ethane system behaves almost ideally, and the largest deviations occur
as the mixing ratio approaches the eutectic composition. | astro-ph_EP |
A Northern Ecliptic Survey for Solar System Science: Making an inventory of the Solar System is one of the four fundamental
science requirements for the Large Synoptic Survey Telescope (LSST). The
current baseline footprint for LSST's main Wide-Fast-Deep (WFD) Survey observes
the sky below 0$^\circ$ declination, which includes only half of the ecliptic
plane. Critically, key Solar System populations are asymmetrically distributed
on the sky: they will be entirely missed, or only partially mapped, if only the
WFD occurs. We propose a Northern Ecliptic Spur (NES) mini survey, observing
the northern sky up to +10$^\circ$ ecliptic latitude, to maximize Solar System
science with LSST. The mini survey comprises a total area of $\sim$5800
deg$^2$/604 fields, with 255 observations/field over the decade, split between
g,r, and z bands. Our proposed survey will 1) obtain a census of main-belt
comets; 2) probe Neptune's past migration history, by exploring the resonant
structure of the Kuiper belt and the Neptune Trojan population; 3) explore the
origin of Inner Oort cloud objects and place significant constraints on the
existence of a hypothesized planet beyond Neptune; and 4) enable precise
predictions of KBO stellar occultations. These high-ranked science goals of the
Solar System Science Collaboration are only achievable with this proposed
northern survey. | astro-ph_EP |
The multi-wavelength phase curves of small bodies: Phase coloring: Context. Small bodies change their brightness due to different motives:
Rotation along their axis or axes, combined with irregular shapes and/or
changing surface properties, or changes in the geometry of observations. In
this work, we tackle the problem of Phase curves, which show the change in
brightness due to changes in the fraction of illuminated surface as seen by the
observer. Aims. We aim to study the effect of the phase curves in the five
wavelengths of the Sloan Digital Sky Survey in scores of objects (several tens
of thousands), focusing particularly on the spectral slopes and the colors and
their changes with phase angle. Methods. We used a Bayesian inference method
and Monte Carlo techniques to retrieve the absolute magnitudes in five
wavelengths, using the results to study the phase coloring effect in different
bins of the semi-major axis. Results. We obtained absolute magnitudes in the
five filters for over 40 000 objects. Although some outliers are identified,
most of the usual color-color space is recovered by the data presented. We also
detect a dual behavior in the spectral slopes, with a change at
${\alpha\approx}$ 5 deg. | astro-ph_EP |
Meteor observations with Mini-MegaTORTORA wide-field monitoring system: Here we report on the results of meteor observations with 9-channel
Mini-MegaTORTORA (MMT-9) wide-field optical monitoring system with high
temporal resolution. During first 1.5 years of operation more than 90 thousands
of meteors have been detected, at a rate of 300-350 per night, with durations
from 0.1 to 2.5 seconds and angular velocities up to 38 degrees per second. The
faintest detected meteors has the peak brightness about 10 mag, while the
majority - from 4 to 8 mag. Some of the meteors have been observed in BVR
filters simultaneously. Color variations along the trail for them are
determined. All parameters of detected meteors are published online. The
database also includes the information on 10 thousands meteors detected by our
previous FAVOR camera in 2006-2009 years. | astro-ph_EP |
Precession due to a close binary system: An alternative explanation for
ν-Octantis?: We model the secular evolution of a star's orbit when it has a nearby binary
system. We assume a hierarchical triple system where the inter-binary distance
is small in comparison with the distance to the star. We show that the major
secular effect is precession of the star's orbit around the binary system's
centre of mass. We explain how we can obtain this precession rate from the
star's radial velocity data, and thus infer the binary system's parameters. We
show that the secular effect of a nearby binary system on the star's radial
velocity can sometimes mimic a planet. We analyze the radial velocity data for
{\nu}-octantis A which has a nearby companion ({\nu}-octantis B) and we obtain
retrograde precession of (-0.86 \pm 0.02)\degree/yr. We show that if
{\nu}-octantis B was itself a double star, it could mimic a signal with
similarities to that previously identified as a planet of {\nu}-octantis A.
Nevertheless, we need more observations in order to decide in favor of the
double star hypothesis. | astro-ph_EP |
Detection of He I $\lambda10830$ Å absorption on HD 189733 b with
CARMENES high-resolution transmission spectroscopy: We present three transit observations of HD 189733 b obtained with the
high-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal
is detected in the near-infrared He I triplet at 10830 \AA{} in all three
transits. During mid-transit, the mean absorption level is $0.88\pm0.04$ %
measured in a $\pm$10 km s$^{-1}$ range at a net blueshift of $-3.5\pm0.4$ km
s$^{-1}$ (10829.84--10830.57 \AA{}). The absorption signal exhibits radial
velocities of $+6.5\pm3.1$ km s$^{-1}$ and $-12.6\pm1.0$ km s$^{-1}$ during
ingress and egress, respectively; measured in the planetary rest frame. We show
that stellar activity related pseudo-signals interfere with the planetary
atmospheric absorption signal. They could contribute as much as 80% of the
observed signal and might also affect the radial velocity signature, but
pseudo-signals are very unlikely to explain the entire signal. The observed
line ratio between the two unresolved and the third line of the He I triplet is
$2.8\pm0.2$, which strongly deviates from the value expected for an optically
thin atmospheres. When interpreted in terms of absorption in the planetary
atmosphere, this favors a compact helium atmosphere with an extent of only 0.2
planetary radii and a substantial column density on the order of $4\times
10^{12}$ cm$^{-2}$. The observed radial velocities can be understood either in
terms of atmospheric circulation with equatorial superrotation or as a sign of
an asymmetric atmospheric component of evaporating material. We detect no clear
signature of ongoing evaporation, like pre- or post-transit absorption, which
could indicate material beyond the planetary Roche lobe, or radial velocities
in excess of the escape velocity. These findings do not contradict planetary
evaporation, but only show that the detected helium absorption in HD 189733 b
does not trace the atmospheric layers that show pronounced escape signatures. | astro-ph_EP |
ACCESS: An optical transmission spectrum of the high-gravity, hot
Jupiter HAT-P-23b: We present a new ground-based visible transmission spectrum of the
high-gravity, hot Jupiter HAT-P-23b, obtained as part of the ACCESS project. We
derive the spectrum from five transits observed between 2016 and 2018, with
combined wavelength coverage between 5200 {\AA} - 9269 {\AA} in 200 {\AA} bins,
and with a median precision of 247 ppm per bin. HAT-P-23b's relatively high
surface gravity (g ~ 30 m/s^2), combined with updated stellar and planetary
parameters from Gaia DR2, gives a 5-scale-height signal of 384 ppm for a
hydrogen-dominated atmosphere. Bayesian models favor a clear atmosphere for the
planet with the tentative presence of TiO, after simultaneously modeling
stellar contamination, using spots parameter constraints from photometry. If
confirmed, HAT-P-23b would be the first example of a high-gravity gas giant
with a clear atmosphere observed in transmission at optical/NIR wavelengths;
therefore, we recommend expanding observations to the UV and IR to confirm our
results and further characterize this planet. This result demonstrates how
combining transmission spectroscopy of exoplanet atmospheres with long-term
photometric monitoring of the host stars can help disentangle the exoplanet and
stellar activity signals. | astro-ph_EP |
Protons in the near-lunar wake observed by the Sub-keV Atom Reflection
Analyzer on board Chandrayaan-1: Significant proton fluxes were detected in the near wake region of the Moon
by an ion mass spectrometer on board Chandrayaan-1. The energy of these
nightside protons is slightly higher than the energy of the solar wind protons.
The protons are detected close to the lunar equatorial plane at a $140^{\circ}$
solar zenith angle, i.e., ~50$^{\circ}$ behind the terminator at a height of
100 km. The protons come from just above the local horizon, and move along the
magnetic field in the solar wind reference frame. We compared the observed
proton flux with the predictions from analytical models of an electrostatic
plasma expansion into a vacuum. The observed velocity was higher than the
velocity predicted by analytical models by a factor of 2 to 3. The simple
analytical models cannot explain the observed ion dynamics along the magnetic
field in the vicinity of the Moon. | astro-ph_EP |
Making hot Jupiters in stellar clusters II: efficient formation in
binary systems: Observations suggested that the occurrence rate of hot Jupiters (HJs) in open
clusters is largely consistent with the field ($\sim1\%$) but in the
binary-rich cluster M67, the rate is $\sim5\%$. How does the cluster
environment boost HJ formation via the high-eccentricity tidal migration
initiated by the extreme-amplitude von Zeipel-Lidov-Kozai (XZKL) mechanism
forced by a companion star? Our analytical treatment shows that the cluster's
collective gravitational potential alters the companion's orbit slowly, which
may render the star-planet-companion configuration XZKL-favourable, a
phenomenon only possible for very wide binaries. We have also performed direct
Gyr $N$-body simulations of the star cluster evolution and XZKL of planets'
orbit around member stars. We find that an initially-single star may acquire a
companion star via stellar scattering and the companion may enable XZKL in the
planets' orbit. Planets around an initially-binary star may also be
XZKL-activated by the companion. In both scenarios, the companion's orbit has
likely been significantly changed by star scattering and the cluster potential
before XZKL occurs in the planets' orbits. Across different cluster models,
0.8\%-3\% of the planets orbiting initially-single stars have experienced XZKL
while the fraction is 2\%-26\% for initially-binary stars. Notably, the
ejection fraction is similar to or appreciably smaller than XZKL. Around a star
that is binary at 1 Gyr, 13\%-32\% of its planets have undergone XZKL, and
combined with single stars, the overall XZKL fraction is 3\%-21\%, most
affected by the cluster binarity. If 10\% of the stars in M67 host a giant
planet, our model predicts an HJ occurrence rate of $\sim1\%$. We suggest that
HJ surveys target old, high-binarity, not-too-dense open clusters and
prioritise wide binaries to maximise HJ yield. | astro-ph_EP |
X-ray irradiation and evaporation of the four young planets around V1298
Tau: Planets around young stars are thought to undergo atmospheric evaporation due
to the high magnetic activity of the host stars. Here we report on X-ray
observations of V1298 Tau, a young star with four transiting exoplanets. We use
X-ray observations of the host star with Chandra and ROSAT to measure the
current high-energy irradiation level of the planets, and employ a model for
the stellar activity evolution together with exoplanetary mass loss to estimate
the possible evolution of the planets. We find that V1298 Tau is X-ray bright
with $\log L_X$ [erg/s] $=30.1$ and has a mean coronal temperature of $\approx
9$ MK. This places the star amongst the more X-ray luminous ones at this
stellar age. We estimate the radiation-driven mass loss of the exoplanets, and
find that it depends sensitively on the possible evolutionary spin-down tracks
of the star as well as on the current planetary densities. Assuming the planets
are of low density due to their youth, we find that the innermost two planets
can lose significant parts of their gaseous envelopes, and could be evaporated
down to their rocky cores depending on the stellar spin evolution. However, if
the planets are heavier and follow the mass-radius relation of older planets,
then even in the highest XUV irradiation scenario none of the planets is
expected to cross the radius gap into the rocky regime until the system reaches
an age of 5 Gyr. | astro-ph_EP |
Thermosphere and exosphere of Hot-Jupiters: Here we describe the observations and the resulting constraints on the upper
atmosphere (thermosphere and exosphere) of the "Hot-Jupiters". In particular,
observations and theoretical modeling of Hot-Jupiter evaporation are described.
The observations allowed the discovery that the planet orbiting HD209458 has an
extended atmosphere of escaping hydrogen and showed the presence of oxygen and
carbon at very high altitude. These observations give unique constraints on the
escape rate and mechanism in the atmosphere of these planets. The most recent
Lyman-alpha HST observations of HD189733b allows for the first time to compare
the evaporation from two different planets in different environments. Models to
quantify the escape rate from the measured occultation depths, and an energy
diagram to describe the evaporation state of Hot-Jupiters are presented. Using
this diagram, it is shown that few already known planets could be remnants of
formerly giant planets. | astro-ph_EP |
Applying the perturbative integral in aeromaneuvers around Mars to
calculate the cost: The perturbative integral method was applied to quantify the contribution of
external forces during a specific interval of time in trajectories of
spacecraft around asteroids and under the Luni-solar influence. However, this
method has not been used to quantify the contributions of drag in aerocapture
and aerobraking. For this reason, the planet Mars is selected to apply this
method during an aerogravity-assisted maneuver. Several trajectories are
analyzed, making use of a drag device with area to mass ratios varying from 0.0
to 20.0 m2/kg, simulating solar sails or de-orbit devices. The mathematical
model is based in the restricted three-body problem. The use of this maneuver
makes it possible to obtain the variations of energy in the trajectory,
replacing expensive maneuvers based on fuel consumption. To observe the effects
of the maneuvers, different values of pericenter velocity and altitude were
selected for prograde and retrograde orbits. The innovation of this research is
the application of an integral method to quantify the delta-V of the aero
gravity maneuver, comparing the cost of the maneuver with the traditional
methods of space propulsion. The results allow the identification of orbits
with conditions to capture, and the perturbative maps show the velocity
variations. | astro-ph_EP |
Methane on Mars: New insights into the sensitivity of CH4 with the
NOMAD/ExoMars spectrometer through its first in-flight calibration: The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the
ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in
solar occultation, nadir, and limb geometries, and will be able to produce an
outstanding amount of diverse data, mostly focused on properties of the
atmosphere. The infrared channels of the instrument operate by combining an
echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF).
Using in-flight data, we characterized the instrument performance and
parameterized its calibration. In particular: an accurate frequency calibration
was achieved, together with its variability due to thermal effects on the
grating. The AOTF properties and transfer function were also quantified, and we
developed and tested a realistic method to compute the spectral continuum
transmitted through the coupled grating + AOTF system. The calibration results
enabled unprecedented insights into the important problem of the sensitivity of
NOMAD to methane abundances in the atmosphere. We also deeply characterized its
performance under realistic conditions of varying aerosol abundances, diverse
albedos and changing illumination conditions as foreseen over the nominal
mission. The results show that, in low aerosol conditions, NOMAD single
spectrum, 1-sigma sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude
when performing solar occultations, and better than 1 ppbv below 30 km. In
dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir
geometry, results demonstrate that NOMAD will be able to produce seasonal maps
of CH4 with a sensitivity around 5 ppbv over most of planet's surface with
spatial integration over 5x5 degrees bins. Results show also that such numbers
can be improved by a factor of 10 to 30 by data binning. Overall, our results
quantify NOMAD's capability to address the variable aspects of Martian climate. | astro-ph_EP |
A census of $ρ$ Oph candidate members from Gaia DR2: The Ophiuchus cloud complex is one of the best laboratories to study the
earlier stages of the stellar and protoplanetary disc evolution. The wealth of
accurate astrometric measurements contained in the Gaia Data Release 2 can be
used to update the census of Ophiuchus member candidates. We seek to find
potential new members of Ophiuchus and identify those surrounded by a
circumstellar disc. We constructed a control sample composed of 188 bona fide
Ophiuchus members. Using this sample as a reference we applied three different
density-based machine learning clustering algorithms (DBSCAN, OPTICS, and
HDBSCAN) to a sample drawn from the Gaia catalogue centred on the Ophiuchus
cloud. The clustering analysis was applied in the five astrometric dimensions
defined by the three-dimensional Cartesian space and the proper motions in
right ascension and declination. The three clustering algorithms systematically
identify a similar set of candidate members in a main cluster with astrometric
properties consistent with those of the control sample. The increased
flexibility of the OPTICS and HDBSCAN algorithms enable these methods to
identify a secondary cluster. We constructed a common sample containing 391
member candidates including 166 new objects, which have not yet been discussed
in the literature. By combining the Gaia data with 2MASS and WISE photometry,
we built the spectral energy distributions from 0.5 to $22\microm$ for a subset
of 48 objects and found a total of 41 discs, including 11 Class II and 1 Class
III new discs. Density-based clustering algorithms are a promising tool to
identify candidate members of star forming regions in large astrometric
databases. If confirmed, the candidate members discussed in this work would
represent an increment of roughly 40% of the current census of Ophiuchus. | astro-ph_EP |
Bayesian constraints on the origin and geology of exo-planetary material
using a population of externally polluted white dwarfs: White dwarfs that have accreted planetary bodies are a powerful probe of the
bulk composition of exoplanetary material. In this paper, we present a Bayesian
model to explain the abundances observed in the atmospheres of 202 DZ white
dwarfs by considering the heating, geochemical differentiation, and collisional
processes experienced by the planetary bodies accreted, as well as
gravitational sinking. The majority (>60%) of systems are consistent with the
accretion of primitive material. We attribute the small spread in refractory
abundances observed to a similar spread in the initial planet-forming material,
as seen in the compositions of nearby stars. A range in Na abundances in the
pollutant material is attributed to a range in formation temperatures from
below 1,000K to higher than 1,400K, suggesting that pollutant material arrives
in white dwarf atmospheres from a variety of radial locations. We also find
that Solar System-like differentiation is common place in exo-planetary
systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the
accretion of a core-rich fragment of a larger differentiated body to at least a
3sigma significance, whilst one system shows evidence that it accreted a
crust-rich fragment. In systems where the abundances suggest that accretion has
finished (13/202), the total mass accreted can be calculated. The 13 systems
are estimated to have accreted masses ranging from the mass of the Moon to half
that of Vesta. Our analysis suggests that accretion continues for 11Myrs on
average. | astro-ph_EP |
Cool Jupiters greatly outnumber their toasty siblings: Occurrence rates
from the Anglo-Australian Planet Search: Our understanding of planetary systems different to our own has grown
dramatically in the past 30 years. However, our efforts to ascertain the degree
to which the Solar system is abnormal or unique have been hindered by the
observational biases inherent to the methods that have yielded the greatest
exoplanet hauls. On the basis of such surveys, one might consider our planetary
system highly unusual - but the reality is that we are only now beginning to
uncover the true picture. In this work, we use the full eighteen-year archive
of data from the Anglo-Australian Planet Search to examine the abundance of
'Cool Jupiters' - analogs to the Solar system's giant planets, Jupiter and
Saturn. We find that such planets are intrinsically far more common through the
cosmos than their siblings, the hot Jupiters. We find that the occurrence rate
of such 'Cool Jupiters' is $6.73^{+2.09}_{-1.13}$\%, almost an order of
magnitude higher than the occurrence of hot Jupiters (at
$0.84^{+0.70}_{-0.20}$\%). We also find that the occurrence rate of giant
planets is essentially constant beyond orbital distances of $\sim$1\,au. Our
results reinforce the importance of legacy radial velocity surveys for the
understanding of the Solar system's place in the cosmos. | astro-ph_EP |
Six newly-discovered hot Jupiters transiting F/G stars: WASP-87b,
WASP-108b, WASP-109b, WASP-110b, WASP-111b & WASP-112b: We present the discoveries of six transiting hot Jupiters: WASP-87b,
WASP-108b, WASP-109b, WASP-110b, WASP-111b and WASP-112b. The planets have
masses of 0.51--2.2 $M_{\rm Jup}$ and radii of 1.19--1.44 $R_{\rm Jup}$ and are
in orbits of 1.68--3.78 d around stars with masses 0.81--1.50 $M_{\rm \odot}$.
WASP-111b is in a prograde, near-aligned ($\lambda = -5 \pm 16^\circ$),
near-circular ($e < 0.10$ at 2 $\sigma$) orbit around a mid-F star. As tidal
alignment around such a hot star is thought to be inefficient, this suggests
that either the planet migrated inwards through the protoplanetary disc or that
scattering processes happened to leave it in a near-aligned orbit. WASP-111
appears to have transitioned from an active to a quiescent state between the
2012 and 2013 seasons, which makes the system a candidate for studying the
effects of variable activity on a hot-Jupiter atmosphere. We find evidence that
the mid-F star WASP-87 is a visual binary with a mid-G star. Two host stars are
metal poor: WASP-112 has [Fe/H] = $-0.64 \pm 0.15$ and WASP-87 has [Fe/H] =
$-0.41 \pm 0.10$. The low density of WASP-112 (0.81 $M_{\rm \odot}$, $0.80 \pm
0.04$ $\rho_{\rm \odot}$) cannot be matched by standard models for any
reasonable value of the age of the star, suggesting it to be affected by the
"radius anomaly". | astro-ph_EP |
Some Comments on Possible Preferred Directions for the SETI Search: The search for extraterrestrial intelligence by looking for signals from
advanced technological civilizations has been ongoing for some decades. We
suggest that it could possibly be made more efficient by focusing on stars from
which the solar system can be observed via mini-eclipsings of the Sun by
transiting planets. | astro-ph_EP |
Physical Characterization of Warm Spitzer-observed Near-Earth Objects: Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic
spectral features to specific surface mineralogies. The combination of
spectroscopy with albedos and diameters derived from thermal infrared
observations can increase the scientific return beyond that of the individual
datasets. To that end, we have completed a spectroscopic observing campaign to
complement the ExploreNEOs Warm Spitzer program that obtained albedos and
diameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the
results of observations using the low-resolution prism mode (~0.7-2.5 microns)
of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also
include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF
Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared
spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our
survey and 213 observations of 154 objects from the MIT survey). We identify a
taxonomic class for each spectrum and use band parameter analysis to
investigate the mineralogies for the S-, Q-, and V-complex objects. Our
analysis suggests that for spectra that contain near-infrared data but lack the
visible wavelength region, the Bus-DeMeo system misidentifies some S-types as
Q-types. We find no correlation between spectral band parameters and
ExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio
(BAR) correlations with phase angle for Eros and Ivar, but a positive BAR
correlation with phase angle for Ganymed. We find evidence for spectral phase
reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary
chondrite type analog for a subset of our sample. Our resulting proportions of
H, L, and LL ordinary chondrites differ from those calculated for meteorite
falls and in previous studies of ordinary chondrite-like NEOs. | astro-ph_EP |
New and updated convex shape models of asteroids based on optical data
from a large collaboration network: Asteroid modeling efforts in the last decade resulted in a comprehensive
dataset of almost 400 convex shape models and their rotation states. This
amount already provided a deep insight into physical properties of main-belt
asteroids or large collisional families. We aim to increase the number of
asteroid shape models and rotation states. Such results are an important input
for various further studies such as analysis of asteroid physical properties in
different populations, including smaller collisional families, thermophysical
modeling, and scaling shape models by disk-resolved images, or stellar
occultation data. This provides, in combination with known masses, bulk density
estimates, but constrains also theoretical collisional and evolutional models
of the Solar System. We use all available disk-integrated optical data (i.e.,
classical dense-in-time photometry obtained from public databases and through a
large collaboration network as well as sparse-in-time individual measurements
from a few sky surveys) as an input for the convex inversion method, and derive
3D shape models of asteroids, together with their rotation periods and
orientations of rotation axes. The key ingredient is the support of more that
one hundred observers who submit their optical data to publicly available
databases. We present updated shape models for 36 asteroids, for which mass
estimates are currently available in the literature or their masses will be
most likely determined from their gravitational influence on smaller bodies,
which orbital deflection will be observed by the ESA Gaia astrometric mission.
This was achieved by using additional optical data from recent apparitions for
the shape optimization. Moreover, we also present new shape model
determinations for 250 asteroids, including 13 Hungarias and 3 near-Earth
asteroids. | astro-ph_EP |
An Early Look of Comet C/2013 A1 (Siding Spring): Breathtaker or
Nightmare?: The dynamically new comet, C/2013 A1 (Siding Spring), is to make a close
approach to Mars on 2014 October 19 at 18:30 UT at a distance of 40+/-1 Martian
radius. Such extremely rare event offers a precious opportunity for the
spacecrafts on Mars to closely study a dynamically new comet itself as well as
the planet-comet interaction. Meanwhile, the high speed meteoroids released
from C/Siding Spring also pose a threat to physically damage the spacecrafts.
Here we present our observations and modeling results of C/Siding Spring to
characterize the comet and assess the risk posed to the spacecrafts on Mars. We
find that the optical tail of C/Siding Spring is dominated by larger particles
at the time of the observation. Synchrone simulation suggests that the comet
was already active in late 2012 when it was more than 7 AU from the Sun. By
parameterizing the dust activity with a semi-analytic model, we find that the
ejection speed of C/Siding Spring is comparable to comets such as the target of
the Rosetta mission, 67P/Churyumov-Gerasimenko. Under nominal situation, the
simulated dust cone will miss the planet by about 20 Martian radius. At the
extreme ends of uncertainties, the simulated dust cone will engulf Mars, but
the meteoric influx at Mars is still comparable to the nominal sporadic influx,
seemly indicating that intense and enduring meteoroid bombardment due to
C/Siding Spring is unlikely. Further simulation also suggests that
gravitational disruption of the dust tail may be significant enough to be
observable at Earth. | astro-ph_EP |
A Hibonite-Pyroxene Spherule in Allan Hills 77307 (CO3.03): Petrography
and Mineralogy: Hibonite-pyroxene spherules are an extremely rare kind of refractory
inclusion that show a wide range of exotic isotopic properties despite their
defining similarity and simplicity in morphology and mineralogy. One such,
relatively large (about 120 micron diameter), inclusion has been found in one
of the most pristine meteorites, Allan Hills 77307 (a carbonaceous chondrite of
the Ornans group; Petrologic type 3.03). The inclusion consists of two central
hibonite laths of about 30x15 micron surrounded by Al, Ca-rich pyroxene. The
hibonite laths have uniform composition. The composition of pyroxene
surrounding the hibonite is radially homogenously Al,-Ca rich up to about 50-60
microns which transitions to Mg, -Ti rich at the outer boundary.
Hibonite-pyroxene spherule found in ALHA 77307 shares many similarities with
the other previously found hibonite-pyroxene spherules. A distinguishing
feature of the inclusion in ALHA77307 is the presence of two slivers/ wedges at
the opposite outer edge of the hibonite- pyroxene spherule that consist of
rapidly, poorly crystalized, sub-micron minerals with pristine textures. The
pristine petrography and mineralogy of this inclusion allow discernment of the
expected general trend of formation and alteration amongst hibonite-pyroxene
spherules. | astro-ph_EP |
Forthcoming mutual events of planets and astrometric radio sources: Radio astronomy observations of close approaches of the Solar system planets
to compact radio sources as well as radio source occultations by planets may be
of large interest for planetary sciences, dynamical astronomy, and testing
gravity theories. In this paper, we present extended lists of occultations of
astrometric radio sources observed in the framework of various astrometric and
geodetic VLBI programs by planets, and close approaches of planets to radio
sources expected in the nearest years. Computations are made making use of the
EPOS software package. | astro-ph_EP |
WEIRD: Wide-orbit Exoplanet search with InfraRed Direct imaging: We report results from the Wide-orbit Exoplanet search with InfraRed Direct
imaging (WEIRD), a survey designed to search for Jupiter-like companions on
very wide orbits (1000 to 5000 AU) around young stars ($<$120 Myr) that are
known members of moving groups in the solar neighborhood ($<$70 pc). Sharing
the same age, distance, and metallicity as their host while being on large
enough orbits to be studied as "isolated" objects make such companions prime
targets for spectroscopic observations and valuable benchmark objects for
exoplanet atmosphere models. The search strategy is based on deep imaging in
multiple bands across the near-infrared domain. For all 177 objects of our
sample, $z_{ab}^\prime$, $J$, [3.6] and [4.5] images were obtained with
CFHT/MegaCam, GEMINI/GMOS, CFHT/WIRCam, GEMINI/Flamingos-2, and $Spitzer$/IRAC.
Using this set of 4 images per target, we searched for sources with red
$z_{ab}^\prime$ and $[3.6]-[4.5]$ colors, typically reaching good completeness
down to 2Mjup companions, while going down to 1Mjup for some targets, at
separations of $1000-5000$ AU. The search yielded 4 candidate companions with
the expected colors, but they were all rejected through follow-up proper motion
observations. Our results constrain the occurrence of 1-13 Mjup planetary-mass
companions on orbits with a semi-major axis between 1000 and 5000 AU at less
than 0.03, with a 95\% confidence level. | astro-ph_EP |
Trace Elemental Behavior in the Solar Nebula: Synchrotron X-ray
Fluorescence Analyses of CM and CR Chondritic Iron Sulfides and Associated
Metal: We have performed a coordinated focused ion beam (FIB)-scanning and
transmission electron microscopy (S/TEM), electron probe microanalysis
(EMPA)-synchrotron X-ray fluorescence (SXRF) microprobe study to determine
phase-specific microstructural characteristics and high-resolution in situ
trace element concentrations of primary pyrrhotite, pentlandite, and associated
metal grains from chondrules in CM2 and CR2 carbonaceous chondrites. This work
is the first of its kind to link trace element chemical and microstructural
observations in chondritic sulfides in an attempt to determine formation
mechanisms and conditions of primary sulfides in these meteorite groups. SXRF
microprobe analyses allowed the concentrations of the minor and trace elements,
Co, Cu, Ge, Zn, and Se to be quantified, in addition to Fe and Ni, at a spatial
resolution of 2 microns. The similarity between the CM and CR PPI sulfide trace
element patterns provides evidence for a common formation mechanism for this
type of sulfide grain in both meteorite groups. In addition, the SRM sulfide
and metal have comparable trace element patterns that indicates a genetic
relationship between the two, such as sulfidization of metal. Enrichments in
Ni, Co, Cu, and Se are consistent with the chalcophile/siderophile behavior of
these elements. The observed depletions in Ge suggest that it may have been
lost by evaporation or else was never incorporated into the metal or sulfide
precursor materials. The depletion in Zn may also be attributable to
evaporation, but, being partially lithophile, may also have been preferentially
incorporated into silicates during chondrule formation. Trace element
concentrations support crystallization from an immiscible sulfide melt in
chondrules for formation of the PPI grains and sulfidization of metal for the
origin of the SRM grains. | astro-ph_EP |
AMD-stability in presence of first order Mean Motion Resonances: The AMD-stability criterion allows to discriminate between a-priori stable
planetary systems and systems for which the stability is not granted and needs
further investigations. AMD-stability is based on the conservation of the
Angular Momentum Deficit (AMD) in the averaged system at all orders of
averaging. While the AMD criterion is rigorous, the conservation of the AMD is
only granted in absence of mean-motion resonances (MMR). Here we extend the
AMD-stability criterion to take into account mean-motion resonances, and more
specifically the overlap of first order MMR. If the MMR islands overlap, the
system will experience generalized chaos leading to instability. The
Hamiltonian of two massive planets on coplanar quasi-circular orbits can be
reduced to an integrable one degree of freedom problem for period ratios close
to a first order MMR. We use the reduced Hamiltonian to derive a new overlap
criterion for first order MMR. This stability criterion unifies the previous
criteria proposed in the literature and admits the criteria obtained for
initially circular and eccentric orbits as limit cases. We then improve the
definition of AMD-stability to take into account the short term chaos generated
by MMR overlap. We analyze the outcome of this improved definition of
AMD-stability on selected multi-planet systems from the Extrasolar Planets
Encyclopeadia. | astro-ph_EP |
Lunar-like silicate material forms the Earth quasisatellite (469219)
2016 HO3 Kamo`oalewa: Little is known about Earth quasi-satellites, a class of near-Earth small
solar system bodies that orbit the sun but remain close to the Earth, because
they are faint and difficult to observe. Here we use the Large Binocular
Telescope (LBT) and the Lowell Discovery Telescope (LDT) to conduct a
comprehensive physical characterization of quasi-satellite (469219) Kamo`oalewa
and assess its affinity with other groups of near-Earth objects. We find that
(469219) Kamo`oalewa rotates with a period of 28.3 (+1.8/-1.3) minutes and
displays a reddened reflectance spectrum from 0.4-2.2 microns. This spectrum is
indicative of a silicate-based composition, but with reddening beyond what is
typically seen amongst asteroids in the inner solar system. We compare the
spectrum to those of several material analogs and conclude that the best match
is with lunar-like silicates. This interpretation implies extensive space
weathering and raises the prospect that Kamo`oalewa could comprise lunar
material. | astro-ph_EP |
Modeling the flyby anomalies with dark matter scattering: update with
additional data and further predictions: We continue our exploration of whether the flyby anomalies can be explained
by scattering of spacecraft nucleons from dark matter gravitationally bound to
the earth, with the addition of data from five new flybys to that from the
original six. We continue to use our model in which inelastic and elastic
scatterers populate shells generated by the precession of circular orbits with
normals tilted with respect to the earth's axis. With 11 data points and 8
parameters in the model, a statistically meaningful fit is obtained with a
chi-squared of 2.7. We give plots of the anomalous acceleration along the
spacecraft trajectory, and the cumulative velocity change, for the five flybys
which exhibit a significant nonzero anomaly. We also discuss implications of
the fit for dark matter-nucleon cross sections, give the prediction of our fit
for the anomaly to be expected from the future Juno flyby, and give predictions
of our fit for flyby orbit orientation changes. In addition we give formulas
for estimating the flyby temperature increase caused by dark matter inelastic
scattering, and for the fraction of flyby nucleons undergoing such scatters.
Finally, for circular satellite orbits, we give a table of predicted secular
changes in orbit radius. These are much too large to be reasonable -- comparing
with data for COBE and GP-B supplied to us by Edward Wright (after the first
version of this paper was posted), we find that our model predicts changes in
orbit radius that are too large by many orders of magnitude. So the model
studied here is ruled out. We conclude that further modeling of the flyby
anomalies must simultaneously attempt to fit constraints coming from satellite
orbits. | astro-ph_EP |
Direct Imaging Search for Extrasolar Planets in the Pleiades: We carried out an imaging survey for extrasolar planets around stars in the
Pleiades (125 Myr, 135 pc) in the $H$ and $K_{S}$ bands using HiCIAO combined
with the adaptive optics, AO188, on the Subaru telescope. We found 13 companion
candidates fainter than 14.5 mag in the $H$ band around 9 stars. Five of these
13 were confirmed to be background stars by measurement of their proper motion.
One was not found in the second epoch observation, and thus was not a
background or companion object. One had multi-epoch image, but the precision of
its proper motion was not sufficient to conclude whether it was background
object. Four other candidates are waiting for second epoch observations to
determine their proper motion. Finally, the remaining 2 were confirmed to be 60
$M_{J}$ brown dwarf companions orbiting around HD 23514 (G0) and HII 1348 (K5)
respectively, as had been reported in previous studies. In our observations,
the average detection limit for a point source was 20.3 mag in the $H$ band
beyond 1''.5 from the central star. On the basis of this detection limit, we
calculated the detection efficiency to be 90% for a planet with 6 to 12 Jovian
masses and a semi-major axis of 50--1000 AU. For this we extrapolated the
distribution of planet mass and semi-major axis derived from RV observations
and adopted the planet evolution model of Baraffe et al. (2003). As there was
no detection of a planet, we estimated the frequency of such planets to be less
than 17.9% ($2\sigma$) around one star of the Pleiades cluster. | astro-ph_EP |
Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy: We obtained spectra, in the wavelength range \lambda = 995 - 1769 nm, of all
four known planets orbiting the star HR 8799. Using the suite of
instrumentation known as Project 1640 on the Palomar 5-m Hale Telescope, we
acquired data at two epochs. This allowed for multiple imaging detections of
the companions and multiple extractions of low-resolution (R ~ 35) spectra.
Data reduction employed two different methods of speckle suppression and
spectrum extraction, both yielding results that agree. The spectra do not
directly correspond to those of any known objects, although similarities with L
and T-dwarfs are present, as well as some characteristics similar to planets
such as Saturn. We tentatively identify the presence of CH_4 along with NH_3
and/or C_2H_2, and possibly CO_2 or HCN in varying amounts in each component of
the system. Other studies suggested red colors for these faint companions, and
our data confirm those observations. Cloudy models, based on previous
photometric observations, may provide the best explanation for the new data
presented here. Notable in our data is that these presumably co-eval objects of
similar luminosity have significantly different spectra; the diversity of
planets may be greater than previously thought. The techniques and methods
employed in this paper represent a new capability to observe and rapidly
characterize exoplanetary systems in a routine manner over a broad range of
planet masses and separations. These are the first simultaneous spectroscopic
observations of multiple planets in a planetary system other than our own. | astro-ph_EP |
Evidence of fast pebble growth near condensation fronts in the HL Tau
protoplanetary disk: Water and simple organic molecular ices dominate the mass of solid materials
available for planetesimal and planet formation beyond the water snow line.
Here we analyze ALMA long baseline 2.9, 1.3 and 0.87 mm continuum images of the
young star HL Tau, and suggest that the emission dips observed are due to rapid
pebble growth around the condensation fronts of abundant volatile species.
Specifically, we show that the prominent innermost dip at 13 AU is spatially
resolved in the 0.87 mm image, and its center radius is coincident with the
expected mid-plane condensation front of water ice. In addition, two other
prominent dips, at distances of 32 and 63 AU, cover the mid-plane condensation
fronts of pure ammonia or ammonia hydrates and clathrate hydrates (especially
with CO and N$_2$) formed from amorphous water ice. The spectral index map of
HL Tau between 1.3 and 0.87 mm shows that the flux ratios inside the dips are
statistically larger than those of nearby regions in the disk. This variation
can be explained by a model with two dust populations, where most of solid mass
resides in a component that has grown into decimeter size scales inside the
dips. Such growth is in accord with recent numerical simulations of volatile
condensation, dust coagulation and settling. | astro-ph_EP |
The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b,
WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations: We present observations of the Rossiter-McLaughlin effect for the transiting
exoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the
orientations of the planetary orbits with respect to the host stars' rotation
axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde
orbits and be well aligned, having sky-projected spin orbit angles consistent
with zero: {\lambda} = -4.7 \pm 4.0{\deg}, {\lambda} = 15 + 33{\deg}/-43{\deg}
and {\lambda} = -9.7 +9.0{\deg}/-7.7{\deg}, respectively. The host stars have
Teff < 6250 K and conform with the trend of cooler stars having low
obliquities. WASP-38b is a massive planet on a moderately long period,
eccentric orbit so may be expected to have a misaligned orbit given the high
obliquities measured in similar systems. However, we find no evidence for a
large spin-orbit angle. By contrast, WASP-1b joins the growing number of
misaligned systems and has an almost polar orbit, {\lambda} = -79
+4.5{\deg}/-4.3{\deg}. It is neither very massive, eccentric nor orbiting a hot
host star, and therefore does not share the properties of many other misaligned
systems. | astro-ph_EP |
The CORALIE survey for southern extrasolar planets XIX. Brown dwarfs and
stellar companions unveiled by radial velocity and astrometry: A historical planet-search on a sample of 1647 nearby southern main sequence
stars has been ongoing since 1998 with the CORALIE spectrograph at La Silla
Observatory, with a backup subprogram dedicated to the monitoring of binary
stars. We review 25 years of CORALIE measurements and search for Doppler
signals consistent with stellar or brown dwarf companions to produce an updated
catalog of both known and previously unpublished binary stars in the
planet-search sample, assessing the binarity fraction of the stellar population
and providing perspective for more precise planet-search in the binary sample.
We perform new analysis on the CORALIE planet-search sample radial velocity
measurements, searching for stellar companions and obtaining orbital solutions
for both known and new binary systems. We perform simultaneous radial velocity
and proper motion anomaly fits on the subset of these systems for which
Hipparcos and Gaia astrometry measurements are available, obtaining accurate
estimates of true mass for the companions. We find 218 stars in the CORALIE
sample to have at least one stellar companion, 130 of which are not yet
published in the literature and for which we present orbital solutions. The use
of proper motion anomaly allow us to derive true masses for the stellar
companions in 132 systems, which we additionally use to estimate stability
regions for possible planetary companions on circumprimary or circumbinary
orbits. Finally, we produce detection limit maps for each star in the sample
and obtain occurrence rates of $0.43^{+0.23}_{-0.11}\%$ and
$12.69^{+0.87}_{-0.77}\%$ for brown dwarf and stellar companions respectively
in the CORALIE sample. | astro-ph_EP |
Transiting Planet Candidates Beyond the Snow Line Detected by Visual
Inspection of 7557 Kepler Objects of Interest: We visually inspected the light curves of 7557 Kepler Objects of Interest
(KOIs) to search for single transit events (STEs) possibly due to long-period
giant planets. We identified 28 STEs in 24 KOIs, among which 14 events are
newly reported in this paper. We estimate the radius and orbital period of the
objects causing STEs by fitting the STE light curves simultaneously with the
transits of the other planets in the system or with the prior information on
the host star density. As a result, we found that STEs in seven of those
systems are consistent with Neptune- to Jupiter-sized objects of orbital
periods ranging from a few to $\sim$ $20\,\mathrm{yr}$. We also estimate that
$\gtrsim20\%$ of the compact multi-transiting systems host cool giant planets
with periods $\gtrsim 3\,\mathrm{yr}$ on the basis of their occurrence in the
KOIs with multiple candidates, assuming the small mutual inclination between
inner and outer planetary orbits. | astro-ph_EP |
Moderate-Resolution $K$-Band Spectroscopy of Substellar Companion
$κ$ Andromedae b: We present moderate-resolution ($R\sim4000$) $K$ band spectra of the
"super-Jupiter," $\kappa$ Andromedae b. The data were taken with the OSIRIS
integral field spectrograph at Keck Observatory. The spectra reveal resolved
molecular lines from H$_{2}$O and CO. The spectra are compared to a custom
$PHOENIX$ atmosphere model grid appropriate for young planetary-mass objects.
We fit the data using a Markov Chain Monte Carlo forward modeling method. Using
a combination of our moderate-resolution spectrum and low-resolution, broadband
data from the literature, we derive an effective temperature of
$T_\mathrm{eff}$ = 1950 - 2150 K, a surface gravity of $\log g=3.5 - 4.5$, and
a metallicity of [M/H] = $-0.2 - 0.0$. These values are consistent with
previous estimates from atmospheric modeling and the currently favored young
age of the system ($<$50 Myr). We derive a C/O ratio of 0.70$_{-0.24}^{+0.09}$
for the source, broadly consistent with the solar C/O ratio. This, coupled with
the slightly subsolar metallicity, implies a composition consistent with that
of the host star, and is suggestive of formation by a rapid process. The
subsolar metallicity of $\kappa$ Andromedae b is also consistent with
predictions of formation via gravitational instability. Further constraints on
formation of the companion will require measurement of the C/O ratio of
$\kappa$ Andromedae A. We also measure the radial velocity of $\kappa$
Andromedae b for the first time, with a value of
$-1.4\pm0.9\,\mathrm{km}\,\mathrm{s}^{-1}$ relative to the host star. We find
that the derived radial velocity is consistent with the estimated high
eccentricity of $\kappa$ Andromedae b. | astro-ph_EP |
Non-adiabatic tidal oscillations induced by a planetary companion: We calculate the dynamical tides raised by a close planetary companion on
non-rotating stars of $1$ $\text{M}_{\odot}$ and $1.4$ $\text{M}_{\odot}$.
Using the Henyey method, we solve the fully non-adiabatic equations throughout
the star. The horizontal Lagrangian displacement is found to be 10 to 100 times
larger than the equilibrium tide value in a thin region near the surface of the
star. This is because non--adiabatic effects dominate in a region that extends
from below the outer edge of the convection zone up to the stellar surface, and
the equilibrium tide approximation is inconsistent with non--adiabaticity.
Although this approximation generally applies in the low frequency limit, it
also fails in the parts of the convection zone where the forcing frequency is
small but larger than the Brunt-V\"ais\"al\"a frequency. We derive analytical
estimates which give a good approximation to the numerical values of the
magnitude of the ratio of the horizontal and radial displacements at the
surface. The relative surface flux perturbation is also significant, on the
order of 0.1 % for a system modelled on 51 Pegasi b. Observations affected by
the horizontal displacement may therefore be more achievable than previously
thought, and brightness perturbations may be the result of flux perturbations
rather than due to the radial displacement. We discuss the implication of this
on the possibility of detecting such tidally excited oscillations, including
the prospect of utilising the large horizontal motion for observations of
systems such as 51 Pegasi. | astro-ph_EP |
Asteroid 2017 FZ2 et al.: signs of recent mass-shedding from YORP?: The first direct detection of the asteroidal YORP effect, a phenomenon that
changes the spin states of small bodies due to thermal reemission of sunlight
from their surfaces, was obtained for (54509) YORP 2000 PH5. Such an alteration
can slowly increase the rotation rate of asteroids, driving them to reach their
fission limit and causing their disruption. This process can produce binaries
and unbound asteroid pairs. Secondary fission opens the door to the eventual
formation of transient but genetically-related groupings. Here, we show that
the small near-Earth asteroid (NEA) 2017 FZ2 was a co-orbital of our planet of
the quasi-satellite type prior to their close encounter on 2017 March 23.
Because of this flyby with the Earth, 2017 FZ2 has become a non-resonant NEA.
Our N-body simulations indicate that this object may have experienced
quasi-satellite engagements with our planet in the past and it may return as a
co-orbital in the future. We identify a number of NEAs that follow similar
paths, the largest named being YORP, which is also an Earth's co-orbital. An
apparent excess of NEAs moving in these peculiar orbits is studied within the
framework of two orbit population models. A possibility that emerges from this
analysis is that such an excess, if real, could be the result of mass shedding
from YORP itself or a putative larger object that produced YORP. Future
spectroscopic observations of 2017 FZ2 during its next visit in 2018 (and of
related objects when feasible) may be able to confirm or reject this
interpretation. | astro-ph_EP |
The birth environment of the solar system constrained by the relative
abundances of the solar radionuclides: The relative abundances of the radionuclides in the solar system at the time
of its birth are crucial arbiters for competing hypotheses regarding the birth
environment of the Sun. The presence of short-lived radionuclides, as evidenced
by their decay products in meteorites, has been used to suggest that
particular, sometimes exotic, stellar sources were proximal to the Sun's birth
environment. The recent confirmation of neutron star - neutron star (NS-NS)
mergers and associated kilonovae as potentially dominant sources of r-process
nuclides can be tested in the case of the solar birth environment using the
relative abundances of the longer-lived nuclides. Critical analysis of the 15
radionuclides and their stable partners for which abundances and production
ratios are well known suggests that the Sun formed in a typical massive
star-forming region (SFR). The apparent overabundances of short-lived
radionuclides (e.g.\, $^{26} {\rm Al}$, $^{41}{\rm Ca}$, $^{36}{\rm Cl}$) in
the early solar system appears to be an artifact of a heretofore
under-appreciation for the important influences of enrichment by Wolf-Rayet
winds in SFRs. The long-lived nuclides (e.g.\, $^{238}{\rm U}$, $^{244}{\rm
Pu}$, $^{247}{\rm Cr}$, $^{129}{\rm I}$) are consistent with an average time
interval between production events of $10^8$ years, seemingly too short to be
the products of NS-NS mergers alone. The relative abundances of all of these
nuclides can be explained by their mean decay lifetimes and an average
residence time in the ISM of $\sim200$ Myr. This residence time evidenced by
the radionuclides is consistent with the average lifetime of dust in the ISM
and the timescale for converting molecular cloud mass to stars. | astro-ph_EP |
ALMA Observations of the DART Impact: Characterizing the Ejecta at
Sub-Millimeter Wavelengths: We report observations of the Didymos-Dimorphos binary asteroid system using
the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Compact
Array (ACA) in support of the Double Asteroid Redirection Test (DART) mission.
Our observations on UT 2022 September 15 provided a pre-impact baseline and the
first measure of Didymos-Dimorphos' spectral emissivity at $\lambda=0.87$ mm,
which was consistent with the handful of siliceous and carbonaceous asteroids
measured at millimeter wavelengths. Our post-impact observations were conducted
using four consecutive executions each of ALMA and the ACA spanning from
T$+$3.52 to T$+$8.60 hours post-impact, sampling thermal emission from the
asteroids and the impact ejecta. We scaled our pre-impact baseline measurement
and subtracted it from the post-impact observations to isolate the flux density
of mm-sized grains in the ejecta. Ejecta dust masses were calculated for a
range of materials that may be representative of Dimorphos' S-type asteroid
material. The average ejecta mass over our observations is consistent with
1.3--6.4$\times10^7$ kg, with the lower and higher values calculated for
amorphous silicates and for crystalline silicates, respectively. Owing to the
likely crystalline nature of S-type asteroid material, the higher value is
favored. These ejecta masses represent 0.3--1.5\% of Dimorphos' total mass and
are in agreement with lower limits on the ejecta mass based on measurements at
optical wavelengths. Our results provide the most sensitive measure of mm-sized
material in the ejecta and demonstrate the power of ALMA for providing
supporting observations to spaceflight missions. | astro-ph_EP |
Sending a Spacecraft to Interstellar Comet 2I/Borisov: In August 2019, a second interstellar object 2I/Borisov was discovered 2
years after the discovery of the first known interstellar object, 1I/'Oumuamua.
Can we send a spacecraft to this object, using existing technologies? In this
paper we assess the technical feasibility of a near-term mission to 2I/Borisov.
We apply the Optimum Interplanetary Trajectory Software (OITS) tool to generate
trajectories to 2I/Borisov. As results, we get the minimal $\Delta V$
trajectory with a launch date in July 2018. For this trajectory, a Falcon Heavy
launcher could have hauled an 8 ton spacecraft to 2I/Borisov. For a later
launch date, results for a combined powered Jupiter flyby with a Solar Oberth
maneuver are presented. For a launch in 2027, we could reach 2I/Borisov in
2052, using the Space Launch System (SLS), up-scaled Parker probe heat shield
technology, and solid propulsion engines. Using a SLS a spacecraft with a mass
of 765 kg could be sent to 2I/Borisov. A Falcon Heavy could deliver 202 kg to
2I/Borisov. Arrival times sooner than 2052 can potentially be achieved but with
higher $\Delta V$ requirements and lower spacecraft payload masses.
2I/Borisov's discovery shortly after the discovery of 1I/'Oumuamua implies that
the next interstellar object might be discovered in the near future. The
feasibility of a mission to both, 1I/'Oumuamua and 2I/Borisov using existing
technologies indicates that missions to at least some future interstellar
objects are feasible as well. | astro-ph_EP |
Hydrogen Greenhouse Planets Beyond the Habitable Zone: We show that collision-induced absorption allows molecular hydrogen to act as
an incondensible greenhouse gas, and that bars or tens of bars of primordial
H2-He mixtures can maintain surface temperatures above the freezing point of
water well beyond the "classical" habitable zone defined for CO2 greenhouse
atmospheres. Using a 1-D radiative-convective model we find that 40 bars of
pure H2 on a 3 Earth-mass planet can maintain a surface temperature of 280K out
to 1.5AU from an early-type M dwarf star and 10 AU from a G-type star.
Neglecting the effects of clouds and of gaseous absorbers besides H2, the flux
at the surface would be sufficient for photosynthesis by cyanobacteria (in the
G star case) or anoxygenic phototrophs (in the M star case). We argue that
primordial atmospheres of one to several hundred bars of H2-He are possible,
and use a model of hydrogen escape to show that such atmospheres are likely to
persist further than 1.5 AU from M stars, and 2 AU from G stars, assuming these
planets have protecting magnetic fields. We predict that the microlensing
planet OGLE-05-390L could have retained a H2-He atmosphere and be habitable at
~2.6 AU from its host M star. | astro-ph_EP |
Peering into the formation history of beta Pictoris b with VLTI/GRAVITY
long baseline interferometry: Our objective is to estimate the C/O ratio in the atmosphere of beta Pictoris
b and obtain an estimate of the dynamical mass of the planet, as well as to
refine its orbital parameters using high-precision astrometry. We used the
GRAVITY instrument with the four 8.2 m telescopes of the Very Large Telescope
Interferometer to obtain K-band spectro-interferometric data on $\beta$ Pic b.
We extracted a medium resolution (R=500) K-band spectrum of the planet and a
high-precision astrometric position. We estimated the planetary C/O ratio using
two different approaches (forward modeling and free retrieval) from two
different codes (ExoREM and petitRADTRANS, respectively). Finally, we used a
simplified model of two formation scenarios (gravitational collapse and
core-accretion) to determine which can best explain the measured C/O ratio. Our
new astrometry disfavors a circular orbit for $\beta$ Pic b
($e=0.15^{+0.05}_{-0.04}$). Combined with previous results and with
Hipparcos/GAIA measurements, this astrometry points to a planet mass of $M =
12.7\pm{}2.2\,M_\mathrm{Jup}$. This value is compatible with the mass derived
with the free-retrieval code petitRADTRANS using spectral data only. The
forward modeling and free-retrieval approches yield very similar results
regarding the atmosphere of beta Pic b. In particular, the C/O ratios derived
with the two codes are identical ($0.43\pm{}0.05$ vs $0.43^{+0.04}_{-0.03}$).
We argue that if the stellar C/O in $\beta$ Pic is Solar, then this combination
of a very high mass and a low C/O ratio for the planet suggests a formation
through core-accretion, with strong planetesimal enrichment. | astro-ph_EP |
Chemical consequences of the C/O ratio on hot Jupiters: Examples from
WASP-12b,CoRoT-2b, XO-1b, and HD 189733b: Motivated by recent spectroscopic evidence for carbon-rich atmospheres on
some transiting exoplanets, we investigate the influence of the C/O ratio on
the chemistry, composition, and spectra of extrasolar giant planets both from a
thermochemical-equilibrium perspective and from consideration of disequilibrium
processes like photochemistry and transport-induced quenching. We find that
although CO is predicted to be a major atmospheric constituent on hot Jupiters
for all C/O ratios, other oxygen-bearing molecules like H2O and CO2 are much
more abundant when C/O < 1, whereas CH4, HCN, and C2H2 gain significantly in
abundance when C/O > 1. Disequilibrium processes tend to enhance the abundance
of CH4, NH3, HCN, and C2H2 over a wide range of C/O ratios. We compare the
results of our models with secondary-eclipse photometric data from the Spitzer
Space Telescope and conclude that (1) disequilibrium models with C/O ~ 1 are
consistent with spectra of WASP-12b, XO-1b, and CoRoT-2b, confirming the
possible carbon-rich nature of these planets, (2) spectra from HD 189733b are
consistent with C/O ~< 1, but as the assumed metallicity is increased above
solar, the required C/O ratio must increase toward 1 to prevent too much H2O
absorption, (3) species like HCN can have a significant influence on spectral
behavior in the 3.6 and 8.0 um Spitzer channels, potentially providing even
more opacity than CH4 when C/O > 1, and (4) the very high CO2 abundance
inferred for HD 189733b from near-infrared observations cannot be explained
through equilibrium or disequilibrium chemistry in a H2-dominated atmosphere.
We discuss possible formation mechanisms for carbon-rich hot Jupiters. The C/O
ratio and bulk atmospheric metallicity provide important clues regarding the
formation and evolution of the giant planets. | astro-ph_EP |
On the frequency of planetary systems around G-dwarfs: We determine the fraction of G-dwarf stars that could host stable planetary
systems based on the observed properties of binaries in the Galactic field, and
in various postulated primordial binary populations, which assume that the
primordial binary fraction is higher than that in the field. We first consider
the frequency of Solar System analogues - planetary systems that form either
around a single G-dwarf star, or a binary containing a G-dwarf where the binary
separation exceeds 100-300au. If the primordial binary fraction and period
distribution is similar to that in the field, then up to 63 per cent of G-dwarf
systems could potentially host a Solar System analogue. However, if the
primordial binary fraction is higher, the fraction of G-dwarf systems that
could host a planetary system like our own is lowered to 38 per cent.
We extend our analysis to consider the fraction of G-dwarf systems (both
single and binary) that can host either circumprimary planets (orbiting the
primary star of the binary) or circumbinary planets (orbiting both stars in the
binary) for fiducial planetary separations between 1 - 100au. Depending on the
assumed binary population, in the circumprimary case between 65 and 95 per cent
of systems can host a planet at 1au, decreasing to between 20 and 65 per cent
of systems that can host a planet at 100au. In the circumbinary case, between 5
and 59 per cent of systems can host a planet at 1au, increasing to between 34
and 75 per cent of systems that can host a planet at 100au.
Our results suggest that the assumed binary fraction is the key parameter in
determining the fraction of potentially stable planetary systems in G-dwarf
systems and that using the present-day value may lead to significant
overestimates if the binary fraction was initially higher. | astro-ph_EP |
High-temperature Dust Condensation around an AGB Star: Evidence from a
Highly Pristine Presolar Corundum: Corundum ($\alpha$-Al$_{2}$O$_{3}$) and amorphous or metastable
Al$_{2}$O$_{3}$ are common components of circumstellar dust observed around
O-rich asymptotic giant branch (AGB) stars and found in primitive meteorites.
We report a detailed isotopic and microstructural investigation of a unique
presolar corundum grain, QUE060, identified in an acid residue of the Queen
Alexandra Range 97008 (LL3.05) meteorite. Based on its O and Mg isotopic
compositions, this 1.4 $\mu$m diameter grain formed in a low- or
intermediate-mass AGB star. It has four developed rhombohedral $\{$011$\}$
faces of corundum and a rough, rounded face with cavities. High Mg contents
(Mg/Al $>$ 0.004) are due to the decay of radioactive $^{26}$Al. No spinel
(MgAl$_{2}$O$_{4}$) inclusions that might have exsolved from the corundum are
observed, but there are several high-Mg domains with modulated structures. The
subhedral shape of grain QUE060 is the first clear evidence that corundum
condenses and grows to micrometer sizes in the extended atmospheres around AGB
stars. The flat faces indicate that grain QUE060 experienced little
modification by gas-grain and grain-grain collisions in the interstellar medium
(ISM) and solar nebula. The Mg distribution in its structure indicates that
grain QUE060 has not experienced any severe heating events since the exhaustion
of $^{26}$Al. However, it underwent at least one very transient heating event
to form the high-Mg domains. A possible mechanism for producing this transient
event, as well as the one rough surface and cavity, is a single grain-grain
collision in the ISM. These results indicate that grain QUE060 is the most
pristine circumstellar corundum studied to date. | astro-ph_EP |
Detection of Na in WASP-21b's lower and upper atmosphere: Optical transmission spectroscopy provides crucial constraints on the
reference pressure levels and scattering properties for hot Jupiter
atmospheres. For certain planets, where alkali atoms are detected in the
atmosphere, their line profiles could serve as a good probe to link upper and
lower atmospheric layers. WASP-21b is a Saturn-mass hot Jupiter orbiting a
thick disc star, with a low density and an equilibrium temperature of 1333 K,
which makes it a good target for transmission spectroscopy. Here, we present a
low-resolution transmission spectrum for WASP-21b based in one transit observed
by the OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias (GTC), and a
high-resolution transmission spectrum based in three transits observed by
HARPS-N at Telescopio Nazinale Galileo (TNG) and HARPS at the ESO 3.6 m
telescope. We performed spectral retrieval analysis on GTC's low-resolution
transmission spectrum and report the detection of Na at a confidence level of
$>$3.5-$\sigma$. The Na line exhibits a broad line profile that can be
attributed to pressure broadening, indicating a mostly clear planetary
atmosphere. The spectrum shows a tentative excess absorption at the K D$_1$
line. Using HARPS-N and HARPS, we spectrally resolved the Na doublet
transmission spectrum. An excess absorption at the Na doublet is detected
during the transit, and shows a radial velocity shift consistent with the
planet orbital motion. We proposed a metric to quantitatively distinguish hot
Jupiters with relatively clear atmospheres from others, and WASP-21b has the
largest metric value among all the characterized hot Jupiters. The detection of
Na at both lower and upper atmosphere of WASP-21b reveals that it is an ideal
target for future follow-up observations, providing the opportunity to
understand the nature of its atmosphere across a wide range of pressure levels. | astro-ph_EP |
Orbital evolution of potentially habitable planets of tidally
interacting binary stars: We simulate the coupled stellar and tidal evolution of short-period binary
stars (orbital period $P_{orb} \lsim$8 days) to investigate the orbital
oscillations, instellation cycles, and orbital stability of circumbinary
planets (CBPs). We consider two tidal models and show that both predict an
outward-then-inward evolution of the binary's semi-major axis $a_{bin}$ and
eccentricity $e_{bin}$. This orbital evolution drives a similar evolution of
the minimum CBP semi-major axis for orbital stability. By expanding on previous
models to include the evolution of the mass concentration, we show that the
maximum in the CBP orbital stability limit tends to occur 100 Myr after the
planets form, a factor of 100 longer than previous investigations. This result
provides further support for the hypothesis that the early stellar-tidal
evolution of binary stars has removed CBPs from short-period binaries. We then
apply the models to Kepler-47 b, a CBP orbiting close to its host stars'
stability limit, to show that if the binary's initial $e_{bin} \gsim$0.24, the
planet would have been orbiting within the instability zone in the past and
probably wouldn't have survived. For stable, hypothetical cases in which the
stability limit does not reach a planet's orbit, we find that the amplitudes of
$a_{bin}$ and $e_{bin}$ oscillations can damp by up to 10\% and 50\%,
respectively. Finally, we consider equal-mass stars with $P_{orb} =$ 7.5 days
and compare the HZ to the stability limit. We find that for stellar masses
$\lsim0.12M_{\odot}$, the HZ is completely unstable, even if the binary orbit
is circular. For $e_{bin} \lsim$0.5, that limit increases to $0.17M_{\odot}$,
and the HZ is partially destabilized for stellar masses up to $0.45M_{\odot}$.
These results may help guide searches for potentially habitable CBPs, as well
as characterize their evolution and likelihood to support life after they are
found. | astro-ph_EP |
The DRAKE mission: finding the frequency of life in the Cosmos: In the search for life in the Universe, exoplanets represent numerous natural
experiments in planet formation, evolution, and the emergence of life. This
raises the fascinating prospect of evaluating cosmic life on a statistical
basis. One key statistic is the occurrence rate of life-bearing worlds, $f_{\rm
L}$, the 'frequency of life' term in the famous Drake Equation. Measuring
$f_{\rm L}$ would give profound insight into how common life is and may help to
constrain origin-of-life theories. I propose $f_{\rm L}$ as the goal for the
DRAKE mission (Dedicated Research for Advancing Knowledge of Exobiology): a
transit spectroscopy survey of M-dwarf habitable zone terrestrial planets. I
investigate how the uncertainty on the observed value of $f_{\rm L}$ scales
with sample size. I determine that sampling error dominates over observational
error and that the uncertainty is a function of the observed $f_{\rm L}$ value.
I show that even small sample sizes can provide significant constraints on
$f_{\rm L}$, boding well for the transit spectroscopy approach. I perform a
feasibility study of the DRAKE mission using a nominal instrument design and
mission plan. Due to low observing efficiencies, DRAKE may need to be
incorporated into a wider-ranging deep-space or lunar observatory. A 50-planet
survey could constrain $f_{\rm L}$ to $\leq$ 0.06 (at 95% confidence) if the
sample $f_{\rm L}$ = 0, or 0.03-0.2 if the sample $f_{\rm L}$ = 0.1. This can
be achieved (on average) in 10 years using a 17-m telescope with an
unrestricted field-of-regard. DRAKE is a viable approach to attempting the
first experimental measurement of $f_{\rm L}$. | astro-ph_EP |
TOI-1468: A system of two transiting planets, a super-Earth and a
mini-Neptune, on opposite sides of the radius valley: We report the discovery and characterization of two small transiting planets
orbiting the bright M3.0V star TOI-1468 (LSPM J0106+1913), whose transit
signals were detected in the photometric time series in three sectors of the
TESS mission. We confirm the e planetary nature of both of them using precise
radial velocity measurements from the CARMENES and MAROON-X spectrographs, and
supplement them with ground-based transit photometry. A joint analysis of all
these data reveals that the shorter-period planet, TOI-1468 b ($P_{\rm b}$ =
1.88 d), has a planetary mass of $M_{\rm b} = 3.21\pm0.24$ $M_{\oplus}$ and a
radius of $R_{\rm b} =1.280^{+0.038}_{-0.039} R_{\oplus}$, resulting in a
density of $\rho_{\rm b} = 8.39^{+ 1.05}_{- 0.92}$ g cm$^{-3}$, which is
consistent with a mostly rocky composition. For the outer planet, TOI-1468 c
($P_{\rm c} = 15.53$ d), we derive a mass of $M_{\rm c} = 6.64^{+ 0.67}_{-
0.68}$ $M_{\oplus}$, a radius of $R_{\rm c} = 2.06\pm0.04\,R_{\oplus}$, and a
bulk density of $\rho_{c} = 2.00^{+ 0.21}_{- 0.19}$ g cm$^{-3}$, which
corresponds to a rocky core composition with a H/He gas envelope. These planets
are located on opposite sides of the radius valley, making our system an
interesting discovery as there are only a handful of other systems with the
same properties. This discovery can further help determine a more precise
location of the radius valley for small planets around M dwarfs and, therefore,
shed more light on planet formation and evolution scenarios. | astro-ph_EP |
The fragmentation criteria in local vertically stratified
self-gravitating disk simulations: Massive circumstellar disks are prone to gravitational instabilities, which
trigger the formation of spiral arms that can fragment into bound clumps under
the right conditions. Two dimensional simulations of self-gravitating disks are
useful starting points for studying fragmentation, allowing for high-resolution
simulations of thin disks. However, convergence issues can arise in 2D from
various sources. One of these sources is the 2D approximation of self-gravity,
which exaggerates the effect of self-gravity on small scales when the potential
is not smoothed to account for the assumed vertical extent of the disk. This
effect is enhanced by increased resolution, resulting in fragmentation at
longer cooling timescales $\beta$. If true, it suggests that the 3D simulations
of disk fragmentation may not have the same convergence problem and could be
used to examine the nature of fragmentation without smoothing self-gravity on
scales similar to the disk scale height. To that end, we have carried out local
3D self-gravitating disk simulations with simple $\beta$ cooling with fixed
background irradiation to determine if 3D is necessary to properly describe
disk fragmentation. Above a resolution of $\sim 40$ grid cells per scale
height, we find that our simulations converge with respect to the cooling
timescale. This result converges in agreement with analytic expectations which
place a fragmentation boundary at $\beta_\mathrm{crit} = 3$. | astro-ph_EP |
Korean-Japanese Planet Search Program: Substellar Companions around
Intermediate-Mass Giants: A Korean-Japanese planet search program has been carried out using the 1.8m
telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea, and the
1.88m telescope at Okayama Astrophysical Observatory (OAO) in Japan to search
for planets around intermediate-mass giant stars. The program aims to show the
properties of planetary systems around such stars by precise Doppler survey of
about 190 G or K type giants together with collaborative surveys of the
East-Asian Planet Search Network. So far, we detected two substellar companions
around massive intermediate-mass giants in the Korean-Japanese planet search
program. One is a brown dwarf-mass companion with 37.6 $M_{\mathrm{J}}$
orbiting a giant HD 119445 with 3.9 $M_{\odot}$, which is the most massive
brown dwarf companion among those found around intermediate-mass giants. The
other is a planetary companion with 1.8 $M_{\mathrm{J}}$ orbiting a giant star
with 2.4 $M_{\odot}$, which is the lowest-mass planetary companion among those
detected around giant stars with $>$ 1.9 $M_{\odot}$. Plotting these systems on
companion mass vs. stellar mass diagram, there seem to exist two unpopulated
regions of substellar companions around giants with 1.5--3 $M_{\odot}$ and
planetary companions orbiting giants with 2.4--4 $M_{\odot}$. The existence of
these possible unpopulated regions supports a current characteristic view that
more massive substellar companions tend to exist around more massive stars. | astro-ph_EP |
HAT-P-54b: A hot jupiter transiting a 0.64 Msun star in field 0 of the
K2 mission: We report the discovery of HAT-P-54b, a planet transiting a late K dwarf star
in field 0 of the NASA K2 mission. We combine ground-based photometric light
curves with radial velocity measurements to determine the physical parameters
of the system. HAT-P-54b has a mass of 0.760 $\pm$ 0.032 $M_J$, a radius of
0.944 $\pm$ 0.028 $R_J$, and an orbital period of 3.7998 d. The star has V =
13.505 $\pm$ 0.060, a mass of 0.645 $\pm$ 0.020 $M_{\odot}$, a radius of 0.617
$\pm$ 0.013 $R_{\odot}$, an effective temperature of Teff = 4390 $\pm$ 50K, and
a subsolar metallicity of [Fe/H] = -0.127 $\pm$ 0.080. HAT-P-54b has a radius
that is smaller than 92% of the known transiting planets with masses greater
than that of Saturn, while HAT-P-54 is one of the lowest-mass stars known to
host a hot Jupiter. Follow-up high-precision photometric observations by the K2
mission promise to make this a well-studied planetary system. | astro-ph_EP |
The Formation Mechanism of Gas Giants on Wide Orbits: The recent discoveries of massive planets on ultra-wide orbits of HR 8799
(Marois et al. 2008) and Fomalhaut (Kalas et al. 2008) present a new challenge
for planet formation theorists. Our goal is to figure out which of three giant
planet formation mechanisms--core accretion (with or without migration),
scattering from the inner disk, or gravitational instability--could be
responsible for Fomalhaut b, HR 8799 b, c and d, and similar planets discovered
in the future. This paper presents the results of numerical experiments
comparing the long-period planet formation efficiency of each possible
mechanism in model A star, G star and M star disks.
First, a simple core accretion simulation shows that planet cores forming
beyond 35 AU cannot reach critical mass, even under the most favorable
conditions one can construct. Second, a set of N-body simulations demonstrates
that planet-planet scattering does not create stable, wide-orbit systems such
as HR 8799. Finally, a linear stability analysis verifies previous work showing
that global spiral instabilities naturally arise in high-mass disks. We
conclude that massive gas giants on stable orbits with semimajor axes greater
than 35 AU form by gravitational instability in the disk. We recommend that
observers examine the planet detection rate as a function of stellar age,
controlling for planet dimming with time. If planet detection rate is found to
be independent of stellar age, it would confirm our prediction that
gravitational instability is the dominant mode of producing detectable planets
on wide orbits. We also predict that the occurrence ratio of long-period to
short-period gas giants should be highest for M dwarfs due to the inefficiency
of core accretion and the expected small fragment mass in their disks. | astro-ph_EP |
Circular periodic orbits, resonance capture and inclination excitation
during type II migration: We consider planetary systems evolving under the effect of a Stokes-type
dissipative force mimicking the outcome of a type II migration process. As
inward migration proceeds and the planets follow the circular family (they
start on circular orbits) and even though they are initially almost coplanar,
resonance capture can be realized. Then, at the \textit{vertical critical
orbits} (VCOs), that the circular family possesses, the inclination excitation
can abruptly take place. The planets are now guided by the spatial elliptic
families, which bifurcate from those critical orbits. We herein, perform a
direct link of mutually inclined stable planetary systems on circular orbits
trapped in \textit{mean-motion resonance} (MMR) with the existence of VCOs of
high values of multiplicity. It is shown that the more the multiplicity of the
periodic orbits of the circular family increases, the more VCOs (corresponding
to more MMRs) appear. In this way, we can provide a justification for the
existence of resonant planets on circular orbits, which could, even further to
that, evolve stably if they were mutually inclined. | astro-ph_EP |
The Atmosphere and Interior Structure of HAT-P-13b from Spitzer
Secondary Eclipses: We present {\em Spitzer} secondary-eclipse observations of the hot Jupiter
HAT-P-13 b in the 3.6 {\micron} and 4.5 {\micron} bands. HAT-P-13 b inhabits a
two-planet system with a configuration that enables constraints on the planet's
second Love number, \math{k\sb{2}}, from precise eccentricity measurements,
which in turn constrains models of the planet's interior structure. We exploit
the direct measurements of \math{e \cos \omega} from our secondary-eclipse data
and combine them with previously published radial velocity data to generate a
refined model of the planet's orbit and thus an improved estimate on the
possible interval for \math{k\sb{2}}. We report eclipse phases of \math{0.49154
\pm 0.00080} and \math{0.49711 \pm 0.00083} and corresponding \math{e \cos
\omega} estimates of \math{-0.0136 \pm 0.0013} and \math{-0.0048 \pm 0.0013}.
Under the assumptions of previous work, our estimate of \math{k\sb{2}} of 0.81
{\pm} 0.10 is consistent with the lower extremes of possible core masses found
by previous models, including models with no solid core. This anomalous result
challenges both interior models and the dynamical assumptions that enable them,
including the essential assumption of apsidal alignment. We also report eclipse
depths of 0.081\% {\pm} 0.008\% in the 3.6 {\micron} channel and 0.088 \% {\pm}
0.028 \% in the 4.5 {\micron} channel. These photometric results are
non-uniquely consistent with solar-abundance composition without any thermal
inversion. | astro-ph_EP |
An extensive radial velocity survey toward NGC 6253: The old and metal rich open cluster NGC 6253 was observed with the FLAMES
multi-object spectrograph during an extensive radial velocity campaign
monitoring 317 stars with a median of 15 epochs per object. All the targeted
stars are located along the upper main sequence of the cluster between 14.8 $<$
V $<$ 16.5. Fifty nine stars are confirmed cluster members both by radial
velocities and proper motions and do not show evidence of variability. We
detected 45 variable stars among which 25 belong to NGC 6253. We were able to
derive an orbital solution for 4 cluster members (and for 2 field stars)
yielding minimum masses in between $\sim$90 M$\rm_J$ and $\sim$460 M$\rm_J$ and
periods between 3 and 220 days. Simulations demonstrated that this survey was
sensitive to objects down to 30 M$\rm_J$ at 10 days orbital periods with a
detection efficiency equal to 50%. On the basis of these results we concluded
that the observed frequency of binaries down to the hydrogen burning limit and
up to 20 days orbital period is around (1.5$\pm$1.3)% in NGC 6253. The overall
observed frequency of binaries around the sample of cluster stars is
(13$\pm$3)%. The median radial velocity precision achieved by the GIRAFFE
spectrograph in this magnitude range was around $\sim$240m$\rm\,s^{-1}$
($\sim$180 m$\rm\,s^{-1}$ for UVES). Based on a limited follow-up analysis of 7
stars in our sample with the HARPS spectrograph we determined that a precision
of 35 m $\rm s^{-1}$ can be reached in this magnitude range, offering the
possibility to further extend the variability analysis into the substellar
domain. Prospects are even more favourable once considering the upcoming
ESPRESSO spectrograph at VLT. | astro-ph_EP |
A sub-Neptune sized planet transiting the M2.5-dwarf G 9-40: Validation
with the Habitable-zone Planet Finder: We validate the discovery of a 2 Earth radii sub-Neptune-size planet around
the nearby high proper motion M2.5-dwarf G 9-40 (EPIC 212048748), using
high-precision near-infrared (NIR) radial velocity (RV) observations with the
Habitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based
photometry with a custom narrow-band photometric filter, and adaptive optics
imaging. At a distance of $d=27.9\mathrm{pc}$, G 9-40b is the second closest
transiting planet discovered by K2 to date. The planet's large transit depth
($\sim$3500ppm), combined with the proximity and brightness of the host star at
NIR wavelengths (J=10, K=9.2) makes G 9-40b one of the most favorable
sub-Neptune-sized planet orbiting an M-dwarf for transmission spectroscopy with
JWST, ARIEL, and the upcoming Extremely Large Telescopes. The star is
relatively inactive with a rotation period of $\sim$29 days determined from the
K2 photometry. To estimate spectroscopic stellar parameters, we describe our
implementation of an empirical spectral matching algorithm using the
high-resolution NIR HPF spectra. Using this algorithm, we obtain an effective
temperature of $T_{\mathrm{eff}}=3404\pm73$K, and metallicity of
$\mathrm{[Fe/H]}=-0.08\pm0.13$. Our RVs, when coupled with the orbital
parameters derived from the transit photometry, exclude planet masses above
$11.7 M_\oplus$ with 99.7% confidence assuming a circular orbit. From its
radius, we predict a mass of $M=5.0^{+3.8}_{-1.9} M_\oplus$ and an RV
semi-amplitude of $K=4.1^{+3.1}_{-1.6}\mathrm{m\:s^{-1}}$, making its mass
measurable with current RV facilities. We urge further RV follow-up
observations to precisely measure its mass, to enable precise transmission
spectroscopic measurements in the future. | astro-ph_EP |
HIFI Observations of Water in the Atmosphere of Comet C/2008 Q3
(Garradd): High-resolution far-infrared and sub-millimetre spectroscopy of water lines
is an important tool to understand the physical and chemical properties of
cometary atmospheres. We present observations of several rotational ortho- and
para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on
Herschel. These observations have provided the first detection of the
2_{12}-1_{01} (1669 GHz) ortho and 1_{11}-0_{00} (1113 GHz) para transitions of
water in a cometary spectrum. In addition, the ground-state transition
1_{10}-1_{01} at 557 GHz is detected and mapped. By detecting several water
lines quasi-simultaneously and mapping their emission we can constrain the
excitation parameters in the coma. Synthetic line profiles are computed using
excitation models which include excitation by collisions, solar infrared
radiation, and radiation trapping. We obtain the gas kinetic temperature,
constrain the electron density profile, and estimate the coma expansion
velocity by analyzing the map and line shapes. We derive water production rates
of 1.7-2.8 x 10^{28} s^{-1} over the range r_h = 1.83-1.85 AU. | astro-ph_EP |
Exoplanets Beyond the Solar Neighbourhood: Galactic Tidal Perturbations: The majority of Milky Way extrasolar planets likely reside within a few kpc
of the Galactic centre. The Galactic tidal forces acting on planets scale
inversely with radius in the Galaxy and so are much greater in the inner Galaxy
than in the Solar neighbourhood. Within a range of 3.5 to 10 kpc, the vertical
tide from the Galactic disc is predominant. Interior to 3.5 kpc, the effects of
the Galactic bulge cannot be neglected and the in-plane tidal components are as
important as the vertical ones. Here, we quantify the orbital changes induced
by these tides. We find that the greatest perturbations occur when the
planetary orbit is severely misaligned to the parent star's orbit. When both
planes are perpendicular, the eccentricity of the planet is driven to unity,
although the semimajor axis is secularly unaffected. When both planes are
coincident, the effect from Galactic tides is minimized, but remains non-zero.
In these cases, we provide estimates for the survival times, as well as the
minimum baseline eccentricity variation for all Milky Way exoplanets as a
function of Galactic parameters. Inclinations similar to the Solar System's
(about 60 degrees) can easily cause eccentric Neptunes (at about 30 AU) around
host stars deep within the Galactic bulge (within 50 pc) to experience
eccentricity variations of several tenths, and cause the exoplanets with the
widest-known separations (at about 1000 AU) to experience similar variations in
the Galactic disc. These variations occur on timescales of a few Gyr, a
fraction of a typical main sequence lifetime. | astro-ph_EP |
Silicon isotopes reveal recycled altered oceanic crust in the mantle
sources of Ocean Island Basalts: The study of silicon (Si) isotopes in ocean island basalts (OIB) has the
potential to discern between different models for the origins of geochemical
heterogeneities in the mantle. Relatively large (several per mil per atomic
mass unit) Si isotope fractionation occurs in low-temperature environments
during biochemical and geochemical precipitation of dissolved Si, where the
precipitate is preferentially enriched in the lighter isotopes relative to the
dissolved Si. In contrast, only a limited range (tenths of a per mil) of Si
isotope fractionation has been observed from high-temperature igneous
processes. Therefore, Si isotopes may be useful as tracers for the presence of
crustal material within OIB mantle source regions that experienced relatively
low-temperature surface processes in a manner similar to other stable isotope
systems, such as oxygen. Characterizing the isotopic composition of the mantle
is also of central importance to the use of the Si isotope system as a basis
for comparisons with other planetary bodies (e.g., Moon, Mars, asteroids).
Here we present the first comprehensive suite of high-precision Si isotope
data obtained by MC-ICP-MS for a diverse suite of OIB. Samples originate from
ocean islands in the Pacific, Atlantic, and Indian Ocean basins and include
representative end-members for the EM-1, EM-2, and HIMU mantle components. On
average, Si isotope compositions of OIB are in general agreement with previous
estimates for the Si isotope composition of bulk silicate Earth. Nonetheless,
some small systematic variations are present; specifically, most HIMU-type
(Mangaia; Cape Verde; La Palma, Canary Islands) and Iceland OIB are enriched in
the lighter isotopes of Si, consistent with recycled altered oceanic crust and
lithospheric mantle in their mantle sources. | astro-ph_EP |
A linear distribution of orbits in compact planetary systems?: We report a linear ordering of orbits in a sample of multiple extrasolar
planetary systems with super-Earth planets. We selected 20 cases, mostly
discovered by the Kepler mission, hosting at least four planets within \sim 0.5
au. The semi-major axis a_n of an n-th planet in each system of this sample
obeys a(n) = a_1 + (n-1) \Delta a, where a_1 is the semi-major axis of the
innermost orbit and \Delta a is a spacing between subsequent planets, which are
specific for a particular system. For instance, the Kepler-33 system hosting
five super-Earth planets exhibits the relative deviations between the observed
and linearly predicted semi-major axes of only a few percent. At least half of
systems in the sample fulfill the linear law with a similar accuracy. We
explain the linear distribution of semi-major axes as a natural implication of
multiple chains of mean motion resonances between subsequent planets, which
emerge due to planet--disk interactions and convergent migration at early
stages of their evolution. | astro-ph_EP |
Detecting Transits of Planetary Companions to Giant Stars: Of the approximately 350 extrasolar planets currently known, of order 10%
orbit evolved stars with radii R >~ 2.5 R_sun. These planets are of particular
interest because they tend to orbit more massive hosts, and have been subjected
to variable stellar insolation over their recent histories as their primaries
evolved off the main sequence. Unfortunately, we have limited information about
the physical properties of these planets, as they were all detected by the
radial velocity method and none have been observed to transit. Here we evaluate
the prospects for detecting transits of planetary companions to giant stars. We
show that several of the known systems have a priori transit probabilities of
>~ 10%, and about one transiting system is expected for the sample of host
stars with R >= 2.5 R_sun. Although the transits are expected to have very
small amplitudes (~few x 10^-4) and long durations (>~ 50 hrs), we argue that
the difficulty with detecting these signals in broadband light is one of
systematic errors and practicality rather than photon noise, even for modest
aperture ~1m telescopes. We propose a novel method that may overcome these
difficulties, which uses narrow-band measurements to isolate the thin ring of
chromospheric emission expected at the limb of giant stars. The transit signals
in these narrow bands are expected to be larger in magnitude and briefer in
duration than in broad-band emission, and thus alleviating many of the
difficulties with transit detection in broad-band emission. Finally, we point
out that it may be possible to discover planetary companions to giant stars
using Kepler, provided that a sufficient number of such targets are monitored. | astro-ph_EP |
Formation of eccentric gas discs from sublimating or partially disrupted
asteroids orbiting white dwarfs: Of the 21 known gaseous debris discs around white dwarfs, a large fraction of
them display observational features that are well described by an eccentric
distribution of gas. In the absence of embedded objects or additional forces,
these discs should not remain eccentric for long timescales, and should instead
circularise due to viscous spreading. The metal pollution and infrared excess
we observe from these stars is consistent with the presence of tidally
disrupted sub-stellar bodies. We demonstrate, using smoothed particle
hydrodynamics, that a sublimating or partially disrupting planet on an
eccentric orbit around a white dwarf will form and maintain a gas disc with an
eccentricity within 0.1 of, and lower than, that of the orbiting body. We also
demonstrate that the eccentric gas disc observed around the white dwarf SDSS
J1228+1040 can be explained by the same hypothesis. | astro-ph_EP |
A possible flyby anomaly for Juno at Jupiter: In the last decades there have been an increasing interest in improving the
accuracy of spacecraft navigation and trajectory data. In the course of this
plan some anomalies have been found that cannot, in principle, be explained in
the context of the most accurate orbital models including all known effects
from classical dynamics and general relativity. Of particular interest for its
puzzling nature, and the lack of any accepted explanation for the moment, is
the flyby anomaly discovered in some spacecraft flybys of the Earth over the
course of twenty years. This anomaly manifest itself as the impossibility of
matching the pre and post-encounter Doppler tracking and ranging data within a
single orbit but, on the contrary, a difference of a few mm$/$s in the
asymptotic velocities is required to perform the fitting.
Nevertheless, no dedicated missions have been carried out to elucidate the
origin of this phenomenon with the objective either of revising our
understanding of gravity or to improve the accuracy of spacecraft Doppler
tracking by revealing a conventional origin.
With the occasion of the Juno mission arrival at Jupiter and the close flybys
of this planet, that are currently been performed, we have developed an orbital
model suited to the time window close to the perijove. This model shows that an
anomalous acceleration of a few mm$/$s$^2$ is also present in this case. The
chance for overlooked conventional or possible unconventional explanations is
discussed. | astro-ph_EP |
Excitation Properties of Photopigments and Their Possible Dependence on
the Host Star: Photosynthesis is a plausible pathway for the sustenance of a substantial
biosphere on an exoplanet. In fact, it is also anticipated to create
distinctive biosignatures detectable by next-generation telescopes. In this
work, we explore the excitation features of photopigments that harvest
electromagnetic radiation by constructing a simple quantum-mechanical model.
Our analysis suggests that the primary Earth-based photopigments for
photosynthesis may not function efficiently at wavelengths $> 1.1$ $\mu$m. In
the context of (hypothetical) extrasolar photopigments, we calculate the
potential number of conjugated $\pi$-electrons ($N_\star$) in the relevant
molecules, which can participate in the absorption of photons. By hypothesizing
that the absorption maxima of photopigments are close to the peak spectral
photon flux of the host star, we utilize the model to estimate $N_\star$. As
per our formalism, $N_\star$ is modulated by the stellar temperature, and is
conceivably higher (lower) for planets orbiting stars cooler (hotter) than the
sun; exoplanets around late-type M-dwarfs might require an $N_\star$ twice that
of the Earth. We conclude the analysis with a brief exposition of how our model
could be empirically tested by future observations. | astro-ph_EP |
Mineralogical Characterization and Phase Angle Study of Two Binary
Near-Earth Asteroids, Potential Targets for NASA's Janus Mission: Ground-based characterization of spacecraft targets prior to mission
operations is critical to properly plan and execute measurements. Understanding
surface properties, like mineralogical composition and phase curves (expected
brightness at different viewing geometries) informs data acquisition during the
flybys. Binary near-Earth asteroids (NEA) (35107) 1991 VH and (175706) 1996 FG3
were selected as potential targets of the National Aeronautics and Space
Administration's (NASA) dual spacecraft Janus mission. We observed 1991 VH
using the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, on
July 26, 2008. 1996 FG3 was observed with the IRTF for seven nights during the
spring of 2022. Compositional analysis of 1991 VH revealed that this NEA is
classified as an Sq-type in the Bus-DeMeo taxonomy classification, with a
composition consistent with LL ordinary chondrites. Using thermal modeling, we
computed the thermally corrected spectra for 1996 FG3 and the corresponding
best fit albedo of about 2-3% for the best spectra averaged for each night. Our
spectral analysis indicates that this NEA is a Ch-type. The best possible
meteorite analogs for 1996 FG3, based on curve matching, are two carbonaceous
chondrites, Y-86789 and Murchison. No rotational variation was detected in the
spectra of 1996 FG3, which means there may not be any heterogeneities on the
surface of the primary. However, a clear phase reddening effect was observed in
our data, confirming findings from previous ground-based studies. | astro-ph_EP |
Twenty years of SpeX: Accuracy limits of spectral slope measurements in
asteroid spectroscopy: We examined two decades of SpeX/NASA Infrared Telescope Facility observations
from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the
MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate
uncertainties and systematic errors in reflectance spectral slope measurements
of asteroids. From 628 spectra of 11 solar analogs used for calibration of the
asteroid spectra, we derived an uncertainty of 4.2%/micron on slope
measurements over 0.8 to 2.4 micron. Air mass contributes to -0.92%/micron per
0.1 unit air mass difference between the asteroid and the solar analog, and
therefore for an overall 2.8%/micron slope variability in SMASS and MITHNEOS
designed to operate within 1.0 to 1.3 air mass. No additional observing
conditions (including parallactic angle, seeing and humidity) were found to
contribute systematically to slope change. We discuss implications for asteroid
taxonomic classification works. Uncertainties provided in this study should be
accounted for in future compositional investigation of small bodies to
distinguish intrinsic heterogeneities from possible instrumental effects. | astro-ph_EP |
Elliptical instability in terrestrial planets and moons: The presence of celestial companions means that any planet may be subject to
three kinds of harmonic mechanical forcing: tides, precession/nutation, and
libration. These forcings can generate flows in internal fluid layers, such as
fluid cores and subsurface oceans, whose dynamics then significantly differ
from solid body rotation. In particular, tides in non-synchronized bodies and
libration in synchronized ones are known to be capable of exciting the
so-called elliptical instability, i.e. a generic instability corresponding to
the destabilization of two-dimensional flows with elliptical streamlines,
leading to three-dimensional turbulence. We aim here at confirming the
relevance of such an elliptical instability in terrestrial bodies by
determining its growth rate, as well as its consequences on energy dissipation,
on magnetic field induction, and on heat flux fluctuations on planetary scales.
Previous studies and theoretical results for the elliptical instability are
re-evaluated and extended to cope with an astrophysical context. In particular,
generic analytical expressions of the elliptical instability growth rate are
obtained using a local WKB approach, simultaneously considering for the first
time (i) a local temperature gradient due to an imposed temperature contrast
across the considered layer or to the presence of a volumic heat source and
(ii) an imposed magnetic field along the rotation axis, coming from an external
source. The theoretical results are applied to the telluric planets and moons
of the solar system as well as to three Super-Earths: 55 CnC e, CoRoT-7b, and
GJ 1214b. For the tide-driven elliptical instability in non-synchronized
bodies, only the Early Earth core is shown to be clearly unstable. For the
libration-driven elliptical instability in synchronized bodies, the core of Io
is shown to be stable, contrary to previously thoughts, whereas Europa, 55 CnC
e, CoRoT-7b and GJ 1214b cores can be unstable. The subsurface ocean of Europa
is slightly unstable}. However, these present states do not preclude more
unstable situations in the past. | astro-ph_EP |
Forward and Inverse Modeling of the Emission and Transmission Spectrum
of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds: The Neptune-mass GJ 436b is one of the most-studied transiting exoplanets
with repeated measurements of both its thermal emission and transmission
spectra. We build on previous studies to answer outstanding questions about
this planet, including its potentially high metallicity and tidal heating of
its interior. We present new observations of GJ 436b's thermal emission at 3.6
and 4.5 micron, which reduce uncertainties in estimates of GJ 436b's flux at
those wavelengths and demonstrate consistency between Spitzer observations
spanning more than 7 years. We analyze the Spitzer thermal emission photometry
and Hubble WFC3 transmission spectrum in tandem. We use a powerful dual-pronged
modeling approach, comparing these data to both self-consistent and retrieval
models. We vary the metallicity, intrinsic luminosity from tidal heating,
disequilibrium chemistry, and heat redistribution. We also study the effect of
clouds and photochemical hazes on the spectra, but do not find strong evidence
for either. The self-consistent and retrieval modeling combine to suggest that
GJ 436b has a high atmospheric metallicity, with best fits at or above several
hundred times solar metallicity, tidal heating warming its interior with
best-fit intrinsic effective effective temperatures around 300--350 K, and
disequilibrium chemistry. High metal-enrichments (>600x solar) can only occur
from the accretion of rocky, rather than icy, material. Assuming Tint~300--350
K, we find that Q'~2x10^5--10^6, larger than Neptune's Q', and implying a long
tidal circularization timescale for the planet's orbit. We suggest that
Neptune-mass planets may be a more diverse class than previously imagined, with
metal-enhancements potentially spanning several orders of magnitude, to perhaps
over 1000x solar metallicity. High fidelity observations with instruments like
JWST will be critical for characterizing this diversity. | astro-ph_EP |
MOA-2010-BLG-073L: An M-Dwarf with a Substellar Companion at the
Planet/Brown Dwarf Boundary: We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073,
announced by the Microlensing Observations in Astrophysics survey on
2010-03-18.
This event was remarkable because the source was previously known to be
photometrically variable. Analyzing the pre-event source lightcurve, we
demonstrate that it is an irregular variable over time scales >200d. Its
dereddened color, $(V-I)_{S,0}$, is 1.221$\pm$0.051mag and from our lens model
we derive a source radius of 14.7$\pm$1.3 $R_{\odot}$, suggesting that it is a
red giant star.
We initially explored a number of purely microlensing models for the event
but found a residual gradient in the data taken prior to and after the event.
This is likely to be due to the variability of the source rather than part of
the lensing event, so we incorporated a slope parameter in our model in order
to derive the true parameters of the lensing system.
We find that the lensing system has a mass ratio of q=0.0654$\pm$0.0006. The
Einstein crossing time of the event, $T_{\rm{E}}=44.3$\pm$0.1d, was
sufficiently long that the lightcurve exhibited parallax effects. In addition,
the source trajectory relative to the large caustic structure allowed the
orbital motion of the lens system to be detected. Combining the parallax with
the Einstein radius, we were able to derive the distance to the lens,
$D_L$=2.8$\pm$0.4kpc, and the masses of the lensing objects. The primary of the
lens is an M-dwarf with $M_{L,p}$=0.16$\pm0.03M_{\odot}$ while the companion
has $M_{L,s}$=11.0$\pm2.0M_{\rm{J}}$ putting it in the boundary zone between
planets and brown dwarfs. | astro-ph_EP |
Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)
VI. Non-detection of sodium with HARPS on the bloated super-Neptune WASP-127b: WASP-127b is one of the puffiest exoplanets found to date, with a mass only
$3.4$ Neptune masses, but a radius larger than Jupiter. It is also located at
the border of the Neptune desert, which describes the lack of highly-irradiated
Neptune-sized planets, and which remains poorly understood. Its large scale
height and bright host star make the transiting WASP-127b a valuable target to
characterise in transmission spectroscopy. We use combined EulerCam and TESS
light curves to recalculate the system's parameters. Additionally, we present
an in-depth search for sodium in four transit observations of WASP-127b,
obtained as part of the Hot Exoplanet Atmosphere Resolved with Transit
Spectroscopy (HEARTS) survey with the High Accuracy Radial velocity Planet
Searcher (HARPS) spectrograph. Two nights from this dataset were analysed
independently by another team, claiming a detection of sodium incompatible with
previous studies of data from both ground and space. We show that this large
sodium detection is actually due to contamination from telluric sodium
emissions and the low S/N in the core of the deep stellar sodium lines. When
properly accounting for these effects, the previous sodium signal is reduced to
an absorption of $0.46\pm0.20\%$ ($2.3\sigma$), which is compatible with
analyses of WASP-127b transits carried out with other instruments. We can fit a
Gaussian to the D2 line, however, the D1 line was not detected, indicating an
unusual line ratio if sodium exists in the atmosphere. Follow-up of WASP-127 at
both high-resolution and with high sensitivity will be required to firmly
establish the presence of sodium and analyse its line shape. | astro-ph_EP |
Hydrothermal formation of Clay-Carbonate alteration assemblages in the
Nili Fossae region of Mars: The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has returned
observations of the Nili Fossae region indicating the presence of Mg- carbonate
in small (<10km sq2), relatively bright rock units that are commonly fractured
(Ehlmann et al., 2008b). We have analyzed spectra from CRISM images and used
co-located HiRISE images in order to further characterize these
carbonate-bearing units. We applied absorption band mapping techniques to
investigate a range of possible phyllosilicate and carbonate minerals that
could be present in the Nili Fossae region. We also describe a clay-carbonate
hydrothermal alteration mineral assemblage in the Archean Warrawoona Group of
Western Australia that is a potential Earth analog to the Nili Fossae
carbonate-bearing rock units. We discuss the geological and biological
implications for hydrothermal processes on Noachian Mars. | astro-ph_EP |
Discovery and characterization of the exoplanets WASP-148b and c. A
transiting system with two interacting giant planets: We present the discovery and characterization of WASP-148, a new extrasolar
system that includes at least two giant planets. The host star is a slowly
rotating inactive late-G dwarf with a V=12 magnitude. The planet WASP-148b is a
hot Jupiter of 0.72 R_Jup and 0.29 M_Jup that transits its host with an orbital
period of 8.80 days. We found the planetary candidate with the SuperWASP
photometric survey, then characterized it with the SOPHIE spectrograph. Our
radial velocity measurements subsequently revealed a second planet in the
system, WASP-148c, with an orbital period of 34.5 days and a minimum mass of
0.40 M_Jup. No transits of this outer planet were detected. The orbits of both
planets are eccentric and fall near the 4:1 mean-motion resonances. This
configuration is stable on long timescales, but induces dynamical interactions
so that the orbits differ slightly from purely Keplerian orbits. In particular,
WASP-148b shows transit-timing variations of typically 15 minutes, making it
the first interacting system with transit-timing variations that is detected on
ground-based light curves. We establish that the mutual inclination of the
orbital plane of the two planets cannot be higher than 35 degrees, and the true
mass of WASP-148c is below 0.60 M_Jup. We present photometric and spectroscopic
observations of this system that cover a time span of ten years. We also
provide their Keplerian and Newtonian analyses; these analyses should be
significantly improved through future TESS~observations. | astro-ph_EP |
The Role of Disc Self-Gravity in Circumbinary Planet Systems: II. Planet
Evolution: We present the results of hydrodynamic simulations examining migration and
growth of planets embedded in self-gravitating circumbinary discs. The binary
star parameters are chosen to mimic those of the Kepler-16, -34 and -35
systems; the aim of this study is to examine the role of disc mass in
determining the stopping locations of migrating planets at the edge of the
cavity created by the central binary. Disc self-gravity can cause significant
shrinkage of the cavity for disc masses in excess of 5--10 $\times$ the minimum
mass solar nebula model. Planets forming early in the disc lifetime can migrate
through the disc and stall at locations closer to the central star than is
normally the case for lower mass discs, resulting in closer agreement between
simulated and observed orbital architecture. The presence of a planet orbiting
in the cavity of a massive disc can prevent the cavity size from expanding to
the size of a lower mass disc. As the disc mass reduces over long time scales,
this indicates that circumbinary planet systems retain memory of their initial
conditions. Our simulations produce planetary orbits in good agreement with
Kepler-16b without the need for self-gravity; Kepler-34 analogue systems
produce wide and highly eccentric cavities, and self-gravity improves the
agreement between simulations and data. Kepler-35b is more difficult to explain
in detail due to it's relatively low mass, which results in the simulated
stopping location being at a larger radius than that observed. | astro-ph_EP |
Alfnoor: assessing the information content of Ariel's low resolution
spectra with planetary population studies: The ARIEL Space Telescope will provide a large and diverse sample of
exoplanet spectra, performing spectroscopic observations of about 1000
exoplanets in the wavelength range $0.5 \to 7.8 \; \mu m$. In this paper, we
investigate the information content of ARIEL's Reconnaissance Survey low
resolution transmission spectra. Among the goals of the ARIEL Reconnaissance
Survey is also to identify planets without molecular features in their
atmosphere. In this work, (1) we present a strategy that will allow to select
candidate planets to be reobserved in a ARIEL's higher resolution Tier; (2) we
propose a metric to preliminary classify exoplanets by their atmospheric
composition without performing an atmospheric retrieval; (3) we introduce the
possibility to find other methods to better exploit the data scientific
content. | astro-ph_EP |
The Great Saturn Storm of 2010-2011: In December 2010, a major storm erupted in Saturn's northern hemisphere near
37 degree planetographic latitude. This rather surprising event, occurring at
an unexpected latitude and time, is the sixth "Great White Spot" (GWS) storm
observed over the last century and a half. Such GWS events are planetary-scale
atmospheric phenomena that dramatically change the typically bland appearance
of the planet. Occurring while the Cassini mission was on-orbit at Saturn, the
Great Storm of 2010-2011 was well-suited for intense scrutiny by the suite of
sophisticated instruments onboard the Cassini spacecraft as well by modern
instrumentation on ground-based telescopes and onboard the Hubble Space
Telescope. This GWS erupted on December 5th and generated a major dynamical
disturbance that affected the whole latitude band from 25 deg to 48 deg N.
Lightning events were prominent and detected as outbursts and flashes at both
optical and radio wavelengths. The activity of the head ceased after about
seven months, leaving the cloud structure and ambient winds perturbed. The tops
of the optically dense clouds of the storm's head reached the 300 mbar altitude
level where a mixture of ices was detected. The energetics of the frequency and
power of lightning, as well as the estimated power generated by the latent heat
released in the water-based convection, both indicate that the power released
for the storm was a significant fraction of Saturn's total radiated power. The
effects of the storm propagated into the stratosphere forming two warm
airmasses at the 0.5-5 mbar pressure level altitude. Related to the
stratospheric disturbance, hydrocarbon composition excesses were found. The
decades-long interval between storms is probably related to the insolation
cycle and the long radiative time constant of Saturn's atmosphere, and several
theories for temporarily storing energy have been proposed. | astro-ph_EP |
Resolved near-UV hydrogen emission lines at 40-Myr super-Jovian
protoplanet Delorme 1 (AB)b: Indications of magnetospheric accretion: We have followed up on our observations of the ~ 40-Myr, and still accreting,
PMC Delorme 1 (AB)b. We used high-resolution spectroscopy to characterise the
accretion process further by accessing the wealth of emission lines in the
near-UV. With VLT/UVES, we obtained R ~ 50000 spectroscopy at 330--452 nm.
After separating the emission of the companion from that of the M5 low-mass
binary, we performed a detailed emission-line analysis, which included
planetary accretion shock modelling. We reaffirm ongoing accretion in Delorme 1
(AB)b and report the first detections in a (super-Jovian) protoplanet of
resolved hydrogen line emission in the near-UV (H-gamma, H-delta, H-epsilon, H8
and H9). We tentatively detect H11, H12, He I and Ca II H/K. The analysis
strongly favours a planetary accretion shock with a line-luminosity-based
accretion rate dMp/dt = 2e-8 MJ/yr. The lines are asymmetric and well described
by sums of narrow and broad components with different velocity shifts. Overall
line shapes are best explained by a pre-shock velocity v0 = 170+-30 km/s,
implying a planetary mass Mp = 13+-5 MJ, and number densities n0 ~ 1e13/cc or
n0 ~ 1e11/cc. The higher density implies a small line-emitting area of ~ 1%
relative to the planetary surface. This favours magnetospheric accretion, a
case potentially strengthened by the presence of blueshifted emission in the
asymmetrical profiles.High-resolution spectroscopy offers the opportunity to
resolve line profiles, crucial for studying the accretion process in depth. The
super-Jovian protoplanet Delorme 1 (AB)b is still accreting at ~ 40 Myr. Thus,
Delorme 1 belongs to the growing family of Peter Pan disc systems with
protoplanetary and/or circumplanetary disc(s) far beyond the typically assumed
disc lifetimes. Further observations of this benchmark companion, and its
presumed disc(s), will help answer key questions about the accretion geometry
in PMCs. | astro-ph_EP |
Solving the Alhazen-Ptolemy Problem: Determining Specular Points on
Spherical Surfaces for Radiative Transfer of Titan's Seas: Given a light source, a spherical reflector, and an observer, where on the
surface of the sphere will the light be directly reflected to the observer,
i.e. where is the the specular point? This is known as the Alhazen-Ptolemy
problem, and finding this specular point for spherical reflectors is useful in
applications ranging from computer rendering to atmospheric modeling to GPS
communications. Existing solutions rely upon finding the roots of a quartic
equation and evaluating numerically which root provides the real specular
point. We offer a formulation, and two solutions thereof, for which the correct
root is predeterminable, thereby allowing the construction of the fully
analytical solutions we present. Being faster to compute, our solutions should
prove useful in cases which require repeated calculation of the specular point,
such as Monte-Carlo radiative transfer, including reflections off of Titan's
hydrocarbon seas. | astro-ph_EP |
Dynamical effects on the classical Kuiper Belt during the
excited-Neptune model: The link between the dynamical evolution of the giant planets and the Kuiper
Belt orbital structure can provide clues and insight about the dynamical
history of the Solar System. The classical region of the Kuiper Belt has two
populations (the cold and hot populations) with completely different physical
and dynamical properties. These properties have been explained in the framework
of a subset of the simulations of the Nice Model, in which Neptune remained on
a low-eccentricity orbit (Neptune's eccentricity is never larger than 0.1)
throughout the giant planet instability. However, recent simulations have
showed that the remaining Nice model simulations, in which Neptune temporarily
acquires a large-eccentricity orbit (larger than 0.1), are also consistent with
the preservation of the cold population (inclination smaller than 4 degrees),
if the latter formed in situ. However, the resulting a cold population showed
in many of the simulations eccentricities larger than those observed for the
real population. We focus on a short period of time which is characterized by
Neptune's large eccentricity and a slow precession of Neptune's perihelion. We
show that if self-gravity is considered in the disk, the precession rate of the
particles longitude of perihelion is slowed down. This, combined with the
effect of mutual scattering among the bodies, which spreads all orbital
elements, allows some objects to return to low eccentricities. However, we show
that if the cold population originally had a small total mass, this effect is
negligible. Thus, we conclude that the only possibilities to keep at low
eccentricity some cold-population objects during a high-eccentricity phase of
Neptune are that (i) either Neptune's precession was rapid, as suggested by
Batygin et al. (2011) or (ii) Neptune's slow precession phase was long enough
to allow some particles to experience a full secular cycle. | astro-ph_EP |
OGLE-2017-BLG-1434Lb: Confirmation of a Cold Super-Earth using Keck
Adaptive Optics: The microlensing event OGLE-2017-BLG-1434 features a cold super-Earth planet
which is one of eleven microlensing planets with a planet-host star mass ratio
$q < 1 \times 10^{-4}$. We provide an additional mass-distance constraint on
the lens host using near-infrared adaptive optics photometry from Keck/NIRC2.
We are able to determine a flux excess of $K_L = 16.96 \pm 0.11$ which most
likely comes entirely from the lens star. Combining this with constraints from
the large Einstein ring radius, $\theta_E=1.40 \pm 0.09\;mas$ and OGLE parallax
we confirm this event as a super-Earth with mass $m_p = 4.43 \pm 0.25M_\odot$.
This system lies at a distance of $D_L = 0.86 \pm 0.05\,kpc$ from Earth and the
lens star has a mass of $M_L=0.234\pm0.012M_\odot$. We confirm that with a
star-planet mass ratio of $q=0.57 \times 10^{-4}$, OGLE-2017-BLG-1434 lies near
the inflexion point of the planet-host mass-ratio power law. | astro-ph_EP |
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