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New transit timing observations for GJ 436 b, HAT-P-3 b, HAT-P-19 b,
WASP-3 b, and XO-2 b: We present new transit observations acquired between 2014 and 2018 for the
hot exoplanets GJ 436 b, HAT-P-3 b, HAT-P-19 b, WASP-3 b, and XO-2 b. New
mid-transit times extend the timespan covered by observations of these
exoplanets and allow us to refine their transit ephemerides. All new transits
are consistent with linear ephemerides. | astro-ph_EP |
The role of the general relativity on icy body reservoirs under the
effects of an inner eccentric Jupiter: Recent studies have analyzed the dynamical evolution of outer small body
populations under the effects of an eccentric inner massive perturber. Such
outer reservoirs are composed of particles on prograde and retrograde orbits,
as well as particles whose orbit flips from prograde to retrograde and back
again showing a coupling between the inclination i and the ascending node
longitude \Omega (Type-F particles). We analyze the role of the General
Relativity (GR) on the dynamics of outer particles under the influence of an
inner eccentric Jupiter-mass planet produced by a planetary scattering event.
In particular, we study how the GR affects the dynamical evolution of the outer
Type-F particles, which experience an eccentric Lidov-Kozai mechanism. We carry
out N-body simulations with and without GR effects. When the GR is included,
the extreme values of \Omega are obtained for retrograde inclinations, while
the minimum and maximum inclinations allowed for Type-F particles increase in
comparison with that derived without GR effects. According to this, if the GR
is included in the simulations, the range of prograde (retrograde) inclinations
of the libration region is reduced (increased) respect to that obtained in
absence of GR. We find two new class of particles when the GR effects are
included in the simulations. On the one hand, particles whose orbital plane
flips from prograde to retrograde and back again without experiencing a
coupling between i and \Omega. On the other hand, retrograde particles that
show a strong coupling between i and \Omega. We infer that the GR may
significantly modify the dynamical properties of the outer reservoirs that
evolve under the effects of an eccentric inner perturber. | astro-ph_EP |
Properties of CO$_2$ clathrate hydrates formed in the presence of
MgSO$_4$ solutions with implications for icy moons: There is evidence to suggest that clathrate hydrates have a significant
effect on the surface geology of icy bodies in the Solar System. However the
aqueous environments believed to be present on these bodies are likely to be
saline rather than pure water. Laboratory work to underpin the properties of
clathrates in such environments is lacking. We fill this gap by carrying out a
laboratory investigation of the physical properties of CO$_2$ clathrates
produced in weak aqueous solutions of MgSO$_4$. We use synchrotron X-ray powder
diffraction to investigate clathrates formed at high CO$_2$ pressure in ice
that has formed from aqueous solutions of MgSO$_4$. We measure the thermal
expansion, density and dissociation properties of the clathrates under
temperature conditions similar to those on icy Solar System bodies. We find
that the sulphate solution inhibits the formation of clathrates by lowering
their dissociation temperatures. Hysteresis is found in the thermal expansion
coefficients as clathrates are cooled and heated; we attribute this to the
presence of the salt in solution. The density derived from X-ray powder
diffraction is temperature and pressure dependent. When comparing the density
of CO$_2$ clathrates to that of the solution in which they formed, we conclude
that they sink in the oceans in which they form. We also find that the
polymorph of ice present at low temperatures is Ih rather than Ic, which we
attribute to the presence of the MgSO$_4$. We 1) conclude that the clathrate
density has implications for their behaviour in satellite oceans as their
sinking and floating capabilities are temperature and pressure dependent, 2)
conclude that the presence of MgSO$_4$ inhibits the formation of clathrates and
in some cases may even affect their structure and 3) report the dominance of Ih
throughout the experimental procedure despite Ic being the stable phase at low
temperature. | astro-ph_EP |
A Bayesian Analysis of Technological Intelligence in Land and Oceans: Current research indicates that (sub)surface ocean worlds essentially devoid
of subaerial landmasses (e.g., continents) are common in the Milky Way, and
that these worlds could host habitable conditions, thence raising the
possibility that life and technological intelligence (TI) may arise in such
aquatic settings. It is known, however, that TI on Earth (i.e., humans) arose
on land. Motivated by these considerations, we present a Bayesian framework to
assess the prospects for the emergence of TIs in land- and ocean-based habitats
(LBHs and OBHs). If all factors are equally conducive for TIs to arise in LBHs
and OBHs, we demonstrate that the evolution of TIs in LBHs (which includes
humans) might have very low odds of roughly $1$-in-$10^3$ to $1$-in-$10^4$,
thus outwardly contradicting the Copernican Principle. Hence, we elucidate
three avenues whereby the Copernican Principle can be preserved: (i) the
emergence rate of TIs is much lower in OBHs, (ii) the habitability interval for
TIs is much shorter in OBHs, and (iii) only a small fraction of worlds with
OBHs comprise appropriate conditions for effectuating TIs. We also briefly
discuss methods for empirically falsifying our predictions, and comment on the
feasibility of supporting TIs in aerial environments. | astro-ph_EP |
RISTRETTO: high-resolution spectroscopy at the diffraction limit of the
VLT: RISTRETTO is a visible high-resolution spectrograph fed by an extreme
adaptive optics (XAO) system, to be proposed as a visitor instrument on ESO
VLT. The main science goal of RISTRETTO is the detection and atmospheric
characterization of exoplanets in reflected light, in particular the temperate
rocky planet Proxima b. RISTRETTO will be able to measure albedos and detect
atmospheric features in a number of exoplanets orbiting nearby stars for the
first time. It will do so by combining a high-contrast AO system working at the
diffraction limit of the telescope to a high-resolution spectrograph, via a
7-spaxel integral-field unit (IFU) feeding single-mode fibers. Further science
cases for RISTRETTO include the study of accreting protoplanets such as PDS 70
b & c through spectrally-resolved H-alpha emission; and spatially-resolved
studies of Solar System objects such as icy moons and the ice giants Uranus and
Neptune. The project is in an advanced design phase for the spectrograph and
IFU/fiber-link sub-systems, and a preliminary design phase for the AO
front-end. Construction of the spectrograph and IFU/fiber-link will start at
the end of 2022. RISTRETTO is a pathfinder instrument in view of similar
developments at ESO ELT, in particular the SCAO-IFU mode of ELT-ANDES and the
future ELT-PCS instrument. | astro-ph_EP |
Titan organic aerosols: molecular composition and structure of
laboratory analogues inferred from systematic pyrolysis gas chromatography
mass spectrometry analysis: Numerous studies have been carried out to characterize the chemical
composition of laboratory analogues of Titan aerosols (tholins), but their
molecular composition as well as their structure are still poorly known. If
pyrolysis gas chromatography mass spectrometry (pyr-GCMS) has been used for
years to give clues about this composition, the highly disparate results
obtained can be attributed to the analytical conditions used and/or to
differences in the nature of the analogues studied. In order to have a better
description of Titan tholins molecular composition, we led a systematic
analysis of these materials using pyr-GCMS with two major objectives: (i)
exploring the analytical parameters to estimate the biases this technique can
induce and to find an optimum for analyses allowing the detection of a wide
range of compounds and thus a characterization of the tholins composition as
comprehensive as possible, and (ii) highlighting the role of the CH4 ratio in
the gaseous reactive medium on the tholins molecular structure. With this aim,
we used a radio-frequency plasma discharge to synthetize tholins with different
concentrations of CH4 diluted in N2. The samples were systematically pyrolyzed
from 200 to 600{\deg}C. The extracted gases were then analyzed by GCMS for
their molecular identification. | astro-ph_EP |
Atmospheres as a Window to Rocky Exoplanet Surfaces: As the characterization of exoplanet atmospheres proceeds, providing insights
into atmospheric chemistry and composition, a key question is how much deeper
into the planet we might be able to see from its atmospheric properties alone.
For small planets with modest atmospheres and equilibrium temperatures, the
first layer below the atmosphere will be their rocky surface. For such warm
rocky planets, broadly Venus-like planets, the high temperatures and moderate
pressures at the base of their atmospheres may enable thermochemical
equilibrium between rock and gas. This links the composition of the surface to
that of the observable atmosphere. Using an equilibrium chemistry code, we find
a boundary in surface pressure-temperature space which simultaneously separates
distinct mineralogical regimes and atmospheric regimes, potentially enabling
inference of surface mineralogy from spectroscopic observations of the
atmosphere. Weak constraints on the surface pressure and temperature also
emerge. This regime boundary corresponds to conditions under which SO2 is
oxidized and absorbed by calcium-bearing minerals in the crust, thus the two
regimes reflect the sulphidation of the crust. The existence of these
atmospheric regimes for Venus-like planets is robust to plausible changes in
the elemental composition. Our results pave the way to the prospect of
characterizing exoplanetary surfaces as new data for short period rocky planet
atmospheres emerge. | astro-ph_EP |
On the Low False Positive Probabilities of Kepler Planet Candidates: We present a framework to conservatively estimate the probability that any
particular planet-like transit signal observed by the Kepler mission is in fact
a planet, prior to any ground-based follow-up efforts. We use Monte Carlo
methods based on stellar population synthesis and Galactic structure models,
and report a priori false positive probabilities for every Kepler Object of
Interest in tabular form, assuming a 20% intrinsic occurrence rate of close-in
planets in the radius range 0.5 Rearth < Rp < 20 Rearth. Almost every candidate
has FPP <10%, and over half have FPP <5%. This probability varies most strongly
with the magnitude and Galactic latitude of the Kepler target star, and more
weakly with transit depth. We establish that a single deep high-resolution
image will be an extremely effective follow-up tool for the shallowest
(Earth-sized) transits, providing the quickest route towards probabilistically
"validating" the smallest candidates by potentially decreasing the false
positive probability of an earth-sized transit around a faint star from >10% to
<1%. On the other hand, we show that the most useful follow-up observations for
moderate-depth (super-Earth and Neptune-sized) candidates are shallower AO
imaging and high S/N spectroscopy. Since Kepler has detected many more
planetary signals than can be positively confirmed with ground-based follow-up
efforts in the near term, these calculations will be crucial to using the
ensemble of Kepler data to determine population characteristics of planetary
systems. We also describe how our analysis complements the Kepler team's more
detailed BLENDER false positive analysis for planet validation. | astro-ph_EP |
Bayesian Model Testing of Ellipsoidal Variations on Stars due to Hot
Jupiters: A massive planet closely orbiting its host star creates tidal forces that
distort the typically spherical stellar surface. These distortions, known as
ellipsoidal variations, result in changes in the photometric flux emitted by
the star, which can be detected within the data from the Kepler Space
Telescope. Currently, there exist several models describing such variations and
their effect on the photometric flux. By using Bayesian model testing in
conjunction with the Bayesian-based exoplanet characterization software package
EXONEST, the most probable representation for ellipsoidal variations was
determined for synthetic data and the confirmed hot Jupiter exoplanet
Kepler-13Ab.The most preferred model for ellipsoidal variations observed in the
Kepler-13 light curve was determined to be EVIL-MC. Among the trigonometric
models, the Modified Kane & Gelino model provided the best representation of
ellipsoidal variations for the Kepler-13 system and may serve as a fast
alternative to the more computationally intensive EVIL-MC. The computational
feasibility of directly modeling the ellipsoidal variations of a star are
examined and future work is outlined. Providing a more accurate model of
ellipsoidal variations is expected to result in better planetary mass
estimations. | astro-ph_EP |
Marginalising instrument systematics in HST WFC3 transit lightcurves: Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations
at 1.1-1.7$\mu$m probe primarily the H$_2$O absorption band at 1.4$\mu$m, and
has provided low resolution transmission spectra for a wide range of
exoplanets. We present the application of marginalisation based on Gibson
(2014) to analyse exoplanet transit lightcurves obtained from HST WFC3, to
better determine important transit parameters such as R$_p$/R$_*$, important
for accurate detections of H$_2$O. We approximate the evidence, often referred
to as the marginal likelihood, for a grid of systematic models using the Akaike
Information Criterion (AIC). We then calculate the evidence-based weight
assigned to each systematic model and use the information from all tested
models to calculate the final marginalised transit parameters for both the
band-integrated, and spectroscopic lightcurves to construct the transmission
spectrum. We find that a majority of the highest weight models contain a
correction for a linear trend in time, as well as corrections related to HST
orbital phase. We additionally test the dependence on the shift in spectral
wavelength position over the course of the observations and find that
spectroscopic wavelength shifts $\delta_\lambda(\lambda)$, best describe the
associated systematic in the spectroscopic lightcurves for most targets, while
fast scan rate observations of bright targets require an additional level of
processing to produce a robust transmission spectrum. The use of
marginalisation allows for transparent interpretation and understanding of the
instrument and the impact of each systematic evaluated statistically for each
dataset, expanding the ability to make true and comprehensive comparisons
between exoplanet atmospheres. | astro-ph_EP |
Lunar eclipse induces disturbance in the lunar exosphere: Given the renewed scientific interest in lunar exploration missions, complete
understanding of lunar near surface environment and its exosphere under
different conditions is of paramount importance. Lunar exosphere has been
extensively studied by ground based observations [18,19,20,21,22,23] and
hypothesized by different models[1,2,3,4,5,6,7,8,9,10,11,12,13]. In present
work, we have discussed overlooked possible sources behind changes in the lunar
exosphere when the Moon passes through the penumbra and umbra of the Earth
during a lunar eclipse. The dusty turbulent environment due to planetary shadow
is not only confined to lunar studies and exploration, but it can also be
extended to all terrestrial airless bodies in the universe with a dusty surface
e.g. some planets, planetary satellites, asteroids etc. | astro-ph_EP |
Differences in the gas and dust distribution in the transitional disk of
a sun-like young star, PDS 70: We present ALMA 0.87 mm continuum, HCO+ J=4--3 emission line, and CO J=3--2
emission line data of the disk of material around the young, Sun-like star PDS
70. These data reveal the existence of a possible two component transitional
disk system with a radial dust gap of 0."2 +/- 0."05, an azimuthal gap in the
HCO+ J=4--3 moment zero map, as well as two bridge-like features in the gas
data. Interestingly these features in the gas disk have no analogue in the dust
disk making them of particular interest. We modeled the dust disk using the
Monte Carlo radiative transfer code HOCHUNK3D (Whitney et al. 2013) using a two
disk components. We find that there is a radial gap that extends from 15-60 au
in all grain sizes which differs from previous work. | astro-ph_EP |
No evidence for radius inflation in hot Jupiters from vertical advection
of heat: Understanding the radiative-dynamical coupling between upper photosphere and
deeper atmosphere is a key in understanding the abnormal large radii of hot
Jupiters. One needs very long integration times of 3D general circulation
models (GCMs) with self consistent radiative transfer to achieve a better
understanding of the feedback process between dynamics and radiation. We here
present the longest 3D non-gray GCM study (86000 d) of an ultra hot Jupiter
(WASP-76 b) published to this date that reached a final converged state.
Furthermore, we present a method that can be used to accelerate the path
towards temperature convergence in the deep atmospheric layers. We find that
the final converged temperature profile is cold in the deep atmospheric layers,
lacking any sign of vertical transport of potential temperature by large scale
atmospheric motions. We thus conclude that the coupling between radiation and
dynamics alone is not sufficient to explain the abnormal large radii of
inflated hot gas giants. | astro-ph_EP |
First Near-IR Spectroscopic Survey of Neptune Trojans with JWST:
Distinct Surface Compositions of Red vs Ultra-Red Neptune Trojans: Neptune's Trojan asteroids have been observed to have a variety of optical
colors, most notably red (g $-$ r < 0.75) vs. ultra-red (g $-$ r > 0.75), but
the underlying cause of these different color classifications is unknown.
Near-IR spectroscopy can be used as a probe of the surface composition of these
objects, as broad ice bands for a variety of materials are present in the
near-IR. Here, we present the first results of a spectroscopic survey of
Neptune's Trojan asteroids using the NIRSpec instrument on JWST. We compare the
near-IR spectra of eight Neptune Trojans (NTs) based on different optical color
classifications and with model spectra of different ices. We find that most of
our targets are consistent with a surface covered in a thin layer of H$_2$O and
CO$_2$ ices, while the only NT to reliably be classified as ultra-red is
covered in ice tholins in addition to CO$_2$. Ice tholins are a known reddening
agent when subjected to irradiation, so these results support the hypothesis
that differences in optical color are due to differences in irradiation of the
surfaces of these bodies. Since NTs have very similar orbits and therefore
generally similar levels of irradiation at the current time, our results
suggest that these objects have unique origins or there is ongoing processing
of the surfaces of these objects through stochastic disturbances such as
impacts. | astro-ph_EP |
ExoMol line lists IV: The rotation-vibration spectrum of methane up to
1500 K: A new hot line list is calculated for $^{12}$CH$_4$ in its ground electronic
state. This line list, called 10to10, contains 9.8 billion transitions and
should be complete for temperatures up to 1500 K. It covers the wavelengths
longer than 1 $\mu$m and includes all transitions to upper states with energies
below $hc \cdot 18\,000$ cm$^{-1}$ and rotational excitation up to $J=39$. The
line list is computed using the eigenvalues and eigenfunctions of CH$_4$
obtained by variational solution of the Schr\"{o}dinger equation for the
rotation-vibration motion of nuclei employing program TROVE. An ab initio
dipole moment surface and a new 'spectroscopic' potential energy surface are
used. Detailed comparisons with other available sources of methane transitions
including HITRAN, experimental compilations and other theoretical line lists
show that these sources lack transitions both higher temperatures and near
infrared wavelengths. This line list is suitable for modelling atmospheres of
cool stars and exoplanets. It is available from the CDS database as well as at
www.exomol.com. | astro-ph_EP |
Asteroid models from generalised projections: Essential facts for
asteroid modellers and geometric inverse problem solvers: We present a review of the problem of asteroid shape and spin reconstruction
from generalised projections; i.e., from lightcurves, disk-resolved images,
occultation silhouettes, radar range-Doppler data, and interferometry. The aim
of this text is to summarize all important mathematical facts and proofs
related to this inverse problem, to describe their implications to observers
and modellers, and to provide the reader with all relevant references. | astro-ph_EP |
Trajectory Optimisation of a Swarm Orbiting 67P/Churyumov-Gerasimenko
Maximising Gravitational Signal: Proper modelling of the gravitational fields of irregularly shaped asteroids
and comets is an essential yet challenging part of any spacecraft visit and
flyby to these bodies. Accurate density representations provide crucial
information for proximity missions which rely heavily on it to design safe and
efficient trajectories. This work explores using a spacecraft swarm to maximise
the measured gravitational signal in a hypothetical mission around the comet
67P/Churyumov-Gerasimenko. Spacecraft trajectories are simultaneously
propagated with an evolutionary optimisation approach to maximise overall
signal return. The propagation is based on an open-source polyhedral gravity
model using a detailed mesh of 67P and considers the comet's sidereal rotation.
We compare performance on a mission scenario using one and four spacecraft. The
results show that the swarm achieved almost twice the single spacecraft
coverage over a fixed mission duration. However, optimising for a single
spacecraft results in a more effective trajectory. Overall, this work serves as
a testbed for efficiently designing a set of trajectories in this complex
gravitational environment balancing measured signals and risks in a swarm
scenario.
The codebase and results are publicly available at
https://github.com/rasmusmarak/TOSS | astro-ph_EP |
Sub-Saturn Planet MOA-2008-BLG-310Lb: Likely To Be In The Galactic Bulge: We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and
argue that it is the strongest candidate yet for a bulge planet. Deviations
from the single-lens fit are smoothed out by finite-source effects and so are
not immediately apparent from the light curve. Nevertheless, we find that a
model in which the primary has a planetary companion is favored over the
single-lens model by \Delta\chi^2 ~ 880 for an additional three degrees of
freedom. Detailed analysis yields a planet/star mass ratio
q=(3.3+/-0.3)x10^{-4} and an angular separation between the planet and star
within 10% of the angular Einstein radius. The small angular Einstein radius,
\theta_E=0.155+/-0.011 mas, constrains the distance to the lens to be D_L>6.0
kpc if it is a star (M_L>0.08 M_sun). This is the only microlensing exoplanet
host discovered so far that must be in the bulge if it is a star. By analyzing
VLT NACO adaptive optics images taken near the baseline of the event, we detect
additional blended light that is aligned to within 130 mas of the lensed
source. This light is plausibly from the lens, but could also be due to a
companion to lens or source, or possibly an unassociated star. If the blended
light is indeed due to the lens, we can estimate the mass of the lens,
M_L=0.67+/-0.14 M_sun, planet mass m=74+/-17 M_Earth, and projected separation
between the planet and host, 1.25+/-0.10 AU, putting it right on the "snow
line". If not, then the planet has lower mass, is closer to its host and is
colder. To distinguish among these possibilities on reasonable timescales would
require obtaining Hubble Space Telescope images almost immediately, before the
source-lens relative motion of \mu=5 mas yr^{-1} causes them to separate
substantially. | astro-ph_EP |
Efficient Follow-Up of Exoplanet Transits Using Small Telescopes: This paper is to introduce an online tool for the prediction of exoplanet
transit light curves. Small telescopes can readily capture exoplanet transits
under good weather conditions when the combination of a bright star and a large
transiting exoplanet results in a significant depth of transit. However, in
reality there are many considerations that need to be made in order to obtain
useful measurements. This paper and accompanying website layout a procedure
based on time series differential photometry that has been successfully
employed using 0.4m aperture telescopes to predict the expected precision for a
whole light curve. This enables robust planning to decide whether the
observation of a particular exoplanet transit should be attempted and in
particular to be able to readily see when it should not to be attempted. This
may result in a significant increase in the number of transit observations
captured by non-specialists. The technique and website are also appropriate for
planning a variety of variable star observations where a prediction of the
light curve can be made. | astro-ph_EP |
Long-Term Stability of Tightly Packed Multi-Planet Systems in Prograde,
Coplanar, Circumstellar Orbits within the $α$ Centauri AB System: We perform long-term simulations, up to ten billion years, of closely-spaced
configurations of 2 -- 6 planets, each as massive as the Earth, traveling on
nested orbits about either stellar component in $\alpha$ Centauri AB. The
innermost planet initially orbits at either the inner edge of its star's
empirical habitable zone (HZ) or the inner edge of its star's conservative HZ.
Although individual planets on low inclination, low eccentricity, orbits can
survive throughout the habitable zones of both stars, perturbations from the
companion star require that the minimum spacing of planets in multi-planet
systems within the habitable zones of each star must be significantly larger
than the spacing of similar multi-planet systems orbiting single stars in order
to be long-lived. The binary companion induces a forced eccentricity upon the
orbits of planets in orbit around either star. Planets on appropriately-phased
circumstellar orbits with initial eccentricities equal to their forced
eccentricities can survive on more closely spaced orbits than those with
initially circular orbits, although the required spacing remains higher than
for planets orbiting single stars. A total of up to nine planets on nested
prograde orbits can survive for the current age of the system within the
empirical HZs of the two stars, with five of these orbiting $\alpha$ Centauri B
and four orbiting $\alpha$ Centauri A. | astro-ph_EP |
The Magellan PFS Planet Search Program: Radial Velocity and Stellar
Abundance Analyses of the 360 AU, Metal-Poor Binary "Twins" HD 133131A & B: We present a new precision radial velocity (RV) dataset that reveals multiple
planets orbiting the stars in the $\sim$360 AU, G2$+$G2 "twin" binary HD
133131AB. Our 6 years of high-resolution echelle observations from MIKE and 5
years from PFS on the Magellan telescopes indicate the presence of two
eccentric planets around HD 133131A with minimum masses of 1.43$\pm$0.03 and
0.63$\pm$0.15 $\mathcal{M}_{\rm J}$ at 1.44$\pm$0.005 and 4.79$\pm$0.92 AU,
respectively. Additional PFS observations of HD 133131B spanning 5 years
indicate the presence of one eccentric planet of minimum mass 2.50$\pm$0.05
$\mathcal{M}_{\rm J}$ at 6.40$\pm$0.59 AU, making it one of the longest period
planets detected with RV to date. These planets are the first to be reported
primarily based on data taken with PFS on Magellan, demonstrating the
instrument's precision and the advantage of long-baseline RV observations. We
perform a differential analysis between the Sun and each star, and between the
stars themselves, to derive stellar parameters and measure a suite of 21
abundances across a wide range of condensation temperatures. The host stars are
old (likely $\sim$9.5 Gyr) and metal-poor ([Fe/H]$\sim$-0.30), and we detect a
$\sim$0.03 dex depletion in refractory elements in HD 133131A versus B (with
standard errors $\sim$0.017). This detection and analysis adds to a small but
growing sample of binary "twin" exoplanet host stars with precise abundances
measured, and represents the most metal-poor and likely oldest in that sample.
Overall, the planets around HD 133131A and B fall in an unexpected regime in
planet mass-host star metallicity space and will serve as an important
benchmark for the study of long period giant planets. | astro-ph_EP |
TOI-222: a single-transit TESS candidate revealed to be a 34-day
eclipsing binary with CORALIE, EulerCam and NGTS: We report the period, eccentricity, and mass determination for the TESS
single-transit event candidate TOI-222, which displayed a single 3000 ppm
transit in the TESS two-minute cadence data from Sector 2. We determine the
orbital period via radial velocity measurements (P=33.9,days), which allowed
for ground-based photometric detection of two subsequent transits. Our data
show that the companion to TOI-222 is a low mass star, with a radius of
$0.18_{-0.10}^{+0.39}$ Rsun and a mass of $0.23\pm0.01$ Msun. This discovery
showcases the ability to efficiently discover long-period systems from TESS
single transit events using a combination of radial velocity monitoring coupled
with high precision ground-based photometry. | astro-ph_EP |
An ultra-short period rocky super-Earth orbiting the G2-star HD 80653: Ultra-short period (USP) planets are a class of exoplanets with periods
shorter than one day. The origin of this sub-population of planets is still
unclear, with different formation scenarios highly dependent on the composition
of the USP planets. A better understanding of this class of exoplanets will,
therefore, require an increase in the sample of such planets that have accurate
and precise masses and radii, which also includes estimates of the level of
irradiation and information about possible companions. Here we report a
detailed characterization of a USP planet around the solar-type star HD 80653
$\equiv$ EP 251279430 using the K2 light curve and 108 precise radial
velocities obtained with the HARPS-N spectrograph, installed on the Telescopio
Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet
($R_{b}=1.613\pm0.071 R_{\oplus}$) transiting the star on a short-period orbit
($P_{\rm b}=0.719573\pm0.000021$ d). From our radial velocity measurements, we
constrained the mass of HD 80653 b to $M_{b}=5.60\pm0.43 M_{\oplus}$. We also
detected a clear long-term trend in the radial velocity data. We derived the
fundamental stellar parameters and determined a radius of
$R_{\star}=1.22\pm0.01 R_{\odot}$ and mass of $M_{\star}=1.18\pm0.04
M_{\odot}$, suggesting that HD 80653, has an age of $2.7\pm1.2$ Gyr. The bulk
density ($\rho_{b} = 7.4 \pm 1.1$ g cm$^{-3}$) of the planet is consistent with
an Earth-like composition of rock and iron with no thick atmosphere. Our
analysis of the K2 photometry also suggests hints of a shallow secondary
eclipse with a depth of 8.1$\pm$3.7 ppm. Flux variations along the orbital
phase are consistent with zero. The most important contribution might come from
the day-side thermal emission from the surface of the planet at $T\sim3480$ K. | astro-ph_EP |
KMT-2018-BLG-1990Lb: A Nearby Jovian Planet From A Low-Cadence
Microlensing Field: We report the discovery and characterization of KMT-2018-BLG-1990Lb, a Jovian
planet $(m_p=0.57_{-0.25}^{+0.79}\,M_J)$ orbiting a late M dwarf
$(M=0.14_{-0.06}^{+0.20}\,M_\odot)$, at a distance
$(D_L=1.23_{-0.43}^{+1.06}\,\kpc)$, and projected at $2.6\pm 0.6$ times the
snow line distance, i.e., $a_{\rm snow}\equiv 2.7\,\au (M/M_\odot)$, This is
the second Jovian planet discovered by KMTNet in its low cadence ($0.4\,{\rm
hr}^{-1}$) fields, demonstrating that this population will be well
characterized based on survey-only microlensing data. | astro-ph_EP |
Correction to: Effect of the rotation and tidal dissipation history of
stars on the evolution of close-in planets: This is an erratum for the publication Bolmont & Mathis 2016 (Celestial
Mechanics and Dynamical Astronomy, 126, 275-296,
https://doi.org/10.1007/s10569-016-9690-3). There was a small mistake for the
spin integration of our code which we corrected and we take advantage of this
erratum to investigate a bit further the influence of a planet on the spin of
its host star. | astro-ph_EP |
Asteroid Surface Geophysics: The regolith-covered surfaces of asteroids preserve records of geophysical
processes that have occurred both at their surfaces and sometimes also in their
interiors. As a result of the unique micro-gravity environment that these
bodies posses, a complex and varied geophysics has given birth to fascinating
features that we are just now beginning to understand. The processes that
formed such features were first hypothesised through detailed spacecraft
observations and have been further studied using theoretical, numerical and
experimental methods that often combine several scientific disciplines. These
multiple approaches are now merging towards a further understanding of the
geophysical states of the surfaces of asteroids. In this chapter we provide a
concise summary of what the scientific community has learned so far about the
surfaces of these small planetary bodies and the processes that have shaped
them. We also discuss the state of the art in terms of experimental techniques
and numerical simulations that are currently being used to investigate regolith
processes occurring on small-body surfaces and that are contributing to the
interpretation of observations and the design of future space missions. | astro-ph_EP |
Circumbinary Chaos: Using Pluto's Newest Moon to Constrain the Masses of
Nix & Hydra: The Pluto system provides a unique local laboratory for the study of binaries
with multiple low mass companions. In this paper, we study the orbital
stability of P4, the most recently discovered moon in the Pluto system. This
newfound companion orbits near the plane of the Pluto-Charon binary, roughly
halfway between the two minor moons Nix and Hydra. We use a suite of few body
integrations to constrain the masses of Nix and Hydra, and the orbital
parameters of P4. For the system to remain stable over the age of the Solar
System, the masses of Nix and Hydra likely do not exceed 5e16 kg and 9e16 kg,
respectively. These upper limits assume a fixed mass ratio between Nix and
Hydra at the value implied by their median optical brightness. Our study finds
that stability is more sensitive to their total mass and that a downward
revision of Charon's eccentricity (from our adopted value of 0.0035) is
unlikely to significantly affect our conclusions. Our upper limits are an order
of magnitude below existing astrometric limits on the masses of Nix and Hydra.
For a density at least that of ice, the albedos of Nix and Hydra would exceed
0.3. This constraint implies they are icy, as predicted by giant impact models.
Even with these low masses, P4 only remains stable if its eccentricity e <
0.02. The 5:1 commensurability with Charon is particularly unstable, Combining
stability constraints with the observed mean motion places the preferred orbit
for P4 just exterior to the 5:1 resonance. These predictions will be tested
when the New Horizons satellite visits Pluto. Based on the results for the
Pluto-Charon system, we expect that circumbinary, multi-planet systems will be
more widely spaced than their singleton counterparts. Further, circumbinary
exoplanets close to the three-body stability boundary, such as those found by
Kepler, are less likely to have other companions nearby. | astro-ph_EP |
Spin and orbital dynamics of planets undergoing thermal atmospheric
tides using a vectorial approach: Earth-mass planets are expected to have atmospheres and experience thermal
tides raised by the host star. These tides transfer energy to the planet that
can counter the dissipation from bodily tides. Indeed, even a relatively thin
atmosphere can drive the rotation of these planets away from the synchronous
state. Here we revisit the dynamical evolution of planets undergoing thermal
atmospheric tides. We use a novel approach based on a vectorial formalism,
which is frame independent and valid for any configuration of the system,
including any eccentricity and obliquity values. We provide the secular
equations of motion after averaging over the mean anomaly and the argument of
the pericenter, which are suitable to model the long-term spin and orbital
evolution of the planet. | astro-ph_EP |
Long-term Orbital Period Variation of Hot Jupiters from Transiting Time
Analysis using TESS Survey Data: Many hot Jupiters may experience orbital decays, which are manifested as
long-term transit timing variations. We have analyzed 7068 transits from the
Transiting Exoplanet Survey Satellite (TESS) for a sample of 326 hot Jupiters.
These new mid-transit time data allow us to update ephemerides for these
systems. By combining the new TESS transit timing data with archival data, we
search for possible long-term orbital period variations in these hot Jupiters
using a linear and a quadratic ephemeris model. We identified 26 candidates
that exhibit possible long-term orbital period variations, including 18
candidates with decreasing orbital periods and 8 candidates with increasing
orbital periods. Among them, 12 candidates have failed in our leave-one-out
cross-validation (LOOCV) test and thus should be considered as marginal
candidates. In addition to tidal interaction, alternative mechanisms such as
apsidal precession, R{\o}mer effect, and Applegate effect could also contribute
to the observed period variations. The ephemerides derived in this work are
useful for scheduling follow-up observations for these hot Jupiters in the
future. The Python code used to generate the ephemerides is made available
online. | astro-ph_EP |
Breakup of the Synchronous State of Binary Asteroid Systems: This paper continues the authors' previous work and presents a coplanar
averaged ellipsoid-ellipsoid model of synchronous binary asteroid system (BAS)
plus thermal and tidal effects. Using this model, we analyze the breakup
mechanism of the synchronous BAS. Different from the classical spin-orbit
coupling model which neglects the rotational motion's influence on the orbital
motion, our model considers simultaneously the orbital motion and the
rotational motions. Our findings are following. (1) Stable region of the
secondary's synchronous state is mainly up to the secondary's shape. The
primary's shape has little influence on it. (2) The stable region shrinks
continuously with the increasing value of the secondary's shape parameter
$a_B/b_B$. Beyond the value of $a_B/b_B=\sqrt{2}$, the planar stable region for
the secondary's synchronous rotation is small but not zero. (3) Considering the
BYORP torque, our model shows agreement with the 1-degree of freedom adiabatic
invariance theory in the outwards migration process, but an obvious difference
in the inwards migration process. In particular, our studies show that the
so-called 'long-term' stable equilibrium between the BYORP torque and the tidal
torque is never a real equilibrium state, although the binary asteroid system
can be captured in this state for quite a long time. (4) In case that the
primary's angular velocity gradually reduces due to the YORP effect, the
secondary's synchronous state may be broken when the primary's rotational
motion crosses some major spin-orbit resonances. | astro-ph_EP |
A condensed matter analogy of impact crater formation: Impact craters exist on various solid objects in the planetary system. A
simplified analogy of the process of their formation is here analyzed by
standard solid state physics and the so called dynamic quantized fracture
mechanics. An expression which links the crater volume to the parameters of the
impactor and the target is obtained within the two approaches. For low impactor
energy, this expression is of the same mathematical form as the one resulting
from recent experiments.It is shown that the formation of an impact crater is
possible even without heating of the target, if the critical stress in the
target satisfies certain conditions. The critical value of the stress needed
for the occurence of a fracture is calculated for three craters: two
terrestrial and one lunar crater. The approach presented here uses only
measurable material parameters, and is therefore more realistic than the
treatement of the same problem using the cohesive energy of materials. | astro-ph_EP |
Structure, variability, and origin of the low-latitude nightglow
continuum between 300 and 1,800 nm: Evidence for HO$_2$ emission in the
near-infrared: The Earth's mesopause region between about 75 and 105 km is characterised by
chemiluminescent emission from various lines of different molecules and atoms.
This emission was and is important for the study of the chemistry and dynamics
in this altitude region at nighttime. However, our understanding of molecular
emissions with low intensities and high line densities is still very limited.
Based on 10 years of data from the astronomical X-shooter echelle spectrograph
at Cerro Paranal in Chile, we have characterised in detail this nightglow
(pseudo-)continuum in the wavelength range from 300 to 1,800 nm. We studied the
spectral features, derived continuum components with similar variability,
calculated climatologies, studied the response to solar activity, and even
estimated the effective emission heights. The results indicate that the
nightglow continuum at Cerro Paranal essentially consists of only two
components, which exhibit very different properties. The main structures of
these components peak at 595 and 1,510 nm. While the former was previously
identified as the main peak of the FeO 'orange arc' bands, the latter is a new
discovery. Laboratory data and theory indicate that this feature and other
structures between about 800 and at least 1,800 nm are caused by emission from
HO$_2$. We performed runs with the Whole Atmosphere Community Climate Model
(WACCM) with modified chemistry and found that the total intensity, layer
profile, and variability indeed support this interpretation, where the excited
HO$_2$ radicals are mostly produced from the termolecular recombination of H
and O$_2$. The WACCM results for the continuum at visual wavelengths show good
agreement for FeO from the reaction of Fe and O$_3$. However, the simulated
total emission appears to be too low, which would require additional mechanisms
where the variability is dominated by O$_3$. | astro-ph_EP |
Monitoring polarization in comet 46P/Wirtanen: We measure the degree of linear polarization of comet 46P/Wirtanen during two
months, embracing the perihelion passage in 2018 December with phase angles
ranging from {\alpha}=18.1 to 46.4 deg. The polarimetric response PQ obtained
resembles what was previously found in comet C/1975 V1 (West). This suggests
46P/Wirtanen belongs to a group of comets with high maximum positive
polarization. We conducted BVRI photometry of 46P and found either neutral or
blue colour of its dust which is in good accordance with measurements of C/1975
V1 (West). While aperture-average polarimetry of 46P/Wirtanen reveals a nearly
zero polarization PQ at the lowest phase angle {\alpha} = 18.1 deg,
simultaneous imaging polarimetry suggests that the negative polarization (PQ<0)
arises in a region of within 5000 km of the nucleus, where the negative
polarization could be as strong as PQ=-(1.44 +/- 0.15) percent. This
observation suggests the existence of the circumnucleus halo and that the coma
is populated by at least two types of dust particles. One of those reveals a
low positive polarization at side scattering and high negative polarization
near backscattering. Both polarimetric features are simultaneously produced by
weakly absorbing Mg-rich silicate particles. Another type of dust produces
solely positive polarization that could be attributed to carbonaceous
particles. This composition of 46P/Wirtanen coma appears to be similar with
what was previously found in comet C/1975 V1 (West). | astro-ph_EP |
Detection Efficiency of Asteroid Surveys: A comprehensive characterization of the detection efficiency of nine of the
major asteroid surveys that have been active over the past two decades is
presented. The detection efficiency is estimated on a nightly basis by
comparing the detected asteroids with the complete catalog of known asteroids
propagated to the same observing epoch. Results include a nightly estimate of
the detection efficiency curves as a function of apparent magnitude and
apparent velocity of the asteroids, as well as a cumulative analysis to
estimate the overall performance of each survey. The limiting magnitude
distribution is estimated for each survey, and it is then modeled as a function
of telescope aperture to obtain an estimate over a wide range of apertures. | astro-ph_EP |
On possible types of magnetospheres of hot Jupiters: We show that the orbits of exoplanets of the "hot Jupiter" type, as a rule,
are located close to the Alf\'{v}en point of the stellar wind of the parent
star. At this, many hot Jupiters can be located in the sub-Alf\'{v}en zone in
which the magnetic pressure of the stellar wind exceeds its dynamic pressure.
Therefore, magnetic field of the wind must play an extremely important role for
the flow of the stellar wind around the atmospheres of the hot Jupiters. This
factor must be considered both in theoretical models and in the interpretation
of observational data. The analysis shows that many typical hot Jupiters should
have shock-less intrinsic magnetospheres, which, apparently, do not have
counterparts in the Solar System. Such magnetospheres are characterized,
primarily, by the absence of the bow shock, while the magnetic barrier
(ionopause) is formed by the induced currents in the upper layers of the
ionosphere. We confirmed this inference by the three-dimensional numerical
simulation of the flow of the parent star stellar wind around the hot Jupiter
HD 209458b in which we took into account both proper magnetic field of the
planet and magnetic field of the wind. | astro-ph_EP |
Solid accretion onto planetary cores in radiative disks: The solid accretion rate, necessary to grow gas giant planetary cores within
the disk lifetime, has been a major constraint for theories of planet
formation. We tested the solid accretion rate efficiency on planetary cores of
different masses embedded in their birth disk, by means of 3D
radiation-hydrodynamics, where we followed the evolution of a swarm of embedded
solids of different sizes. We found that using a realistic equation of state
and radiative cooling, the disk at 5 au is able to cool efficiently and reduce
its aspect ratio. As a result, the pebble isolation mass is reached before the
core grows to 10 Earth masses, stopping efficiently the pebble flux and
creating a transition disk. Moreover, the reduced isolation mass halts the
solid accretion before the core reaches the critical mass, leading to a barrier
to giant planet formation, and it explains the large abundance of super-Earth
planets in the observed population. | astro-ph_EP |
Combining Gaia and GRAVITY: Characterising Five New Directly Detected
Substellar Companions: Precise mass constraints are vital for the characterisation of brown dwarfs
and exoplanets. Here, we present how the combination of data obtained by Gaia
and GRAVITY can help enlarge the sample of substellar companions with measured
dynamical masses. We show how the Non-Single-Star (NSS) two-body orbit
catalogue contained in Gaia DR3 can be used to inform high angular resolution
follow-up observations with GRAVITY. Applying the method presented in this work
for eight Gaia candidate systems, we detect all eight predicted companions,
seven of which being previously unknown and five of substellar nature. Among
the sample is Gaia DR3 2728129004119806464 B, which - detected at a angular
separation of (34.01 $\pm$ 0.15) mas from the host - is the closest substellar
companion ever imaged. In combination with the system's distance this
translates to a physical separation of (1.054 $\pm$ 0.002) AU. The GRAVITY data
are then used to break the host-companion mass degeneracy inherent to the Gaia
NSS orbit solutions as well as to constrain the orbital solutions of the
respective target systems. Knowledge of the companion masses enables us to
further characterise them in terms of their age, effective temperature and
radius by the application of evolutionary models. The results serve as an
independent validation of the orbital solutions published in the NSS two-body
orbit catalogue and show that the combination of astrometric survey missions
and high-angular resolution direct imaging hold great promise for efficiently
increasing the sample of directly-imaged companions in the future, especially
in the light of the Gaia's upcoming DR4 and the advent of GRAVITY+. | astro-ph_EP |
Valence-shell photoionization of chlorine-like Ar$^{+}$ ions: Absolute cross-section measurements for valence-shell photoionization of
Ar$^{+}$ ions are reported for photon energies ranging from 27.4 eV to 60.0 eV.
The data, taken by merging beams of ions and synchrotron radiation at a photon
energy resolution of 10 meV, indicate that the primary ion beam was a
statistically weighted mixture of the $^2P^o_{3/2}$ ground state and the
$^2P^o_{1/2}$ metastable state of Ar$^{+}$. Photoionization of this
C$\ell$-like ion is characterized by multiple Rydberg series of autoionizing
resonances superimposed on a direct photoionization continuum. Observed
resonance lineshapes indicate interference between indirect and direct
photoionization channels. Resonance features are spectroscopically assigned and
their energies and quantum defects are tabulated. The measurements are
satisfactorily reproduced by theoretical calculations based on an intermediate
coupling semi-relativistic Breit-Pauli approximation. | astro-ph_EP |
Debris Disks in Multi-Planet Systems: Are Our Inferences Compromised by
Unseen Planets?: Resolved debris disk features (e.g., warps, offsets, edges and gaps,
azimuthal asymmetries, radially thickened rings, scale heights) contain
valuable information about the underlying planetary systems, such as the
posited planet's mass, semi-major axis, and other orbital parameters. Most
existing models assume a single planet is sculpting the disk feature, but
recent observations of mature planetary systems (e.g., by radial velocity
surveys or \textit{Kepler}) have revealed that many planets reside in
multi-planet systems. Here we investigate if/how planet properties inferred
from single-planet models are compromised when multiple planets reside in the
system. For each disk feature, we build a two-planet model that includes a
planet b with fixed parameters and a planet c with a full range of possible
parameters. We investigate these two-planet systems and summarize the
configurations for which assuming a single planet (i.e., planet b) leads to
significantly flawed inferences of that planet's properties. We find that
although disk features are usually primarily dominated by a single planet, when
using single-planet models we are at risk of misinterpreting planet properties
by orders of magnitude in extreme cases. Specifically, we are at high risk of
misinterpreting planet properties from disk warps; at moderate risk from disk
edges and gaps, radially thickened rings, and scale height features; and at low
risk from host star-disk center offsets and azimuthal asymmetries. We summarize
situations where we can infer the need to use a multi-planet model instead of a
single-planet one from disk morphology dissimilarities. | astro-ph_EP |
A new statistical method for characterizing the atmospheres of
extrasolar planets: By detecting light from extrasolar planets,we can measure their compositions
and bulk physical properties. The technologies used to make these measurements
are still in their infancy, and a lack of self-consistency suggests that
previous observations have underestimated their systemic errors.We demonstrate
a statistical method, newly applied to exoplanet characterization, which uses a
Bayesian formalism to account for underestimated errorbars. We use this method
to compare photometry of a substellar companion, GJ 758b, with custom
atmospheric models. Our method produces a probability distribution of
atmospheric model parameters including temperature, gravity, cloud model
(fsed), and chemical abundance for GJ 758b. This distribution is less sensitive
to highly variant data, and appropriately reflects a greater uncertainty on
parameter fits. | astro-ph_EP |
Computing Apparent Planetary Magnitudes for The Astronomical Almanac: Improved equations for computing planetary magnitudes are reported. These
formulas model V-band observations acquired from the time of the earliest
filter photometry in the 1950s up to the present era. The new equations
incorporate several terms that have not previously been used for generating
physical ephemerides. These include the rotation and revolution angles of Mars,
the sub-solar and sub-Earth latitudes of Uranus, and the secular time
dependence of Neptune. Formulas for use in The Astronomical Almanac cover the
planetary phase angles visible from Earth. Supplementary equations cover those
phase angles beyond the geocentric limits. Geocentric magnitudes were computed
over a span of at least 50 years and the results were statistically analyzed.
The mean, variation and extreme magnitudes for each planet are reported. Other
bands besides V on the Johnson-Cousins and Sloan photometric systems are
briefly discussed. The planetary magnitude data products available from the
U.S. Naval Observatory are also listed. An appendix describes source code and
test data sets that are available on-line for computing planetary magnitudes
according to the equations and circumstances given in this paper. The files are
posted as supplementary material for this paper. They are also available at
SourceForge under project
https://sourceforge.net/projects/planetary-magnitudes/ under the 'Files' tab in
the folder 'Ap_Mag_Current_Version'. | astro-ph_EP |
Modeling the Historical Flux of Planetary Impactors: The impact cratering record of the Moon and the terrestrial planets provides
important clues about the formation and evolution of the Solar System.
Especially intriguing is the epoch 3.8-3.9 Gyr ago (Ga), known as the Late
Heavy Bombardment (LHB), when the youngest lunar basins such as Imbrium and
Orientale formed. The LHB was suggested to originate from a slowly declining
impactor flux or from a late dynamical instability. Here we develop a model for
the historical flux of large asteroid impacts and discuss how it depends on
various parameters, including the time and nature of the planetary
migration/instability. We find that the asteroid impact flux dropped by 1 to 2
orders of magnitude during the first 1 Gyr and remained relatively unchanged
over the last 3 Gyr. The early impacts were produced by asteroids whose orbits
became excited during the planetary migration/instability, and by those
originating from the inner extension of the main belt (E-belt; semimajor axis
1.6<a<2.1 au). The profiles obtained for the early and late versions of the
planetary instability initially differ, but end up being similar after ~3 Ga.
Thus, the time of the instability can only be determined by considering the
cratering and other constraints during the first ~1.5 Gyr of the Solar System
history. Our absolute calibration of the impact flux indicates that asteroids
were probably not responsible for the LHB, independently of whether the
instability happened early or late, because the calibrated flux is not large
enough to explain Imbrium/Orientale and a significant share of large lunar
craters. Comets and leftovers of the terrestrial planet formation provided
additional, and probably dominant source of impacts during early epochs. | astro-ph_EP |
HAT-P-42b and HAT-P-43b. Two Inflated Transiting Hot Jupiters from the
HATNet Survey: First identified from the HATNet wide-field photometric survey, these
candidate transiting planets were then followed-up with a variety of
photometric observations. Determining the planetary nature of the objects and
characterizing the parameters of the systems were mainly done with the SOPHIE
spectrograph at the 1.93m telescope at OHP and the TRES spectrograph at the
1.5m telescope at FLWO. HAT-P-42b and HAT-P-43b are typical hot Jupiters on
circular orbits around early-G/late-F main sequence host stars, with periods of
4.641876\pm0.000032 and 3.332688\pm0.000016 days, masses of 0.975\pm0.126 and
0.660\pm0.083 Mjup, and radii of 1.277\pm0.149 and 1.283+0.057-0.034 Rjup,
respectively. These discoveries increase the sample of planets with measured
mean densities, which is needed to constrain theories of planetary interiors
and atmospheres. Moreover, their hosts are relatively bright (V < 13.5)
facilitating further follow-up studies. | astro-ph_EP |
Capture of exocomets and the erosion of the Oort cloud due to stellar
encounters in the Galaxy: The Oort cloud (OC) probably formed more than 4$\,$Gyr ago and has been
moving with the Sun in the Galaxy since, exposed to external influences, most
prominently to the Galactic tide and passing field stars. Theories suggest that
other stars might posses exocomets distributed similarly to our OC. We study
the erosion of the OC and the possibility for capturing exocomets during the
encounters with such field stars. We carry out simulations of flybys, where
both stars are surrounded by a cloud of comets. We measure how many exocomets
are transferred to the OC, how many OC's comets are lost, and how this depends
on the other star's mass, velocity and impact parameter. Exocomets are
transferred to the OC only during relatively slow
($\lesssim0.5\,$km$\,$s$^{-1}$) and close ($\lesssim10^5\,$AU) flybys and these
are expected to be extremely rare. Assuming that all passing stars are
surrounded by a cloud of exocomets, we derive that the fraction of exocomets in
the OC has been about $10^{-5}$--$10^{-4}$. Finally we simulate the OC for the
whole lifetime of the Sun, taking into account the encounters and the tidal
effects. The OC has lost 25--65% of its mass, mainly due to stellar encounters,
and at most 10% (and usually much less) of its mass can be captured. However,
exocomets are often lost shortly after the encounter that delivers them, due to
the Galactic tide and consecutive encounters. | astro-ph_EP |
Dynamics of Colombo's Top: Generating Exoplanet Obliquities from
Planet-Disk Interactions: Large planetary spin-orbit misalignments (obliquities) may strongly influence
atmospheric circulation and tidal heating in the planet. A promising avenue to
generate obliquities is via spin-orbit resonances, where the spin and orbital
precession frequencies of the planet cross each other as the system evolves in
time. One such mechanism involves a dissipating (mass-losing) protoplanetary
disk that drives orbital precession of an interior planet. We study this
scenario analytically in this paper, and obtain the mapping between the general
initial spin orientation and the final obliquity. We show that (i) under
adiabatic evolution (i.e. the disk dissipates at a sufficiently slow rate), the
final planetary obliquity as a function of the initial spin orientation
bifurcates into distinct tracks governed by interactions with the resonance;
(ii) under nonadiabatic evolution, a broad range of obliquities can be excited.
We obtain analytical expressions for the final obliquities for various regimes
of parameter space. The dynamical system studied in this paper is an example of
"Colombo's top", and our analysis and results can be adapted to other
applications. | astro-ph_EP |
Chemically defining the building blocks of the Earth: Chondrites are undifferentiated sediments of material left over from the
earliest solar system and are widely considered as representatives of the
unprocessed building blocks of the terrestrial planets. The chondrites, along
with processed igneous meteorites, have been divided into two broad categories
based upon their isotopic signatures; these have been termed the CC and NC
groups and have been interpreted as reflecting their distinctive birth places
within the solar system. The isotopic distinctiveness of NC and CC meteorites
document limited radial-mixing in the accretionary disk. The enstatite and
ordinary chondrites are NC-type and likely represent samples from inner solar
system (likely $<$4 AU). Measurement and modeling of ratios of refractory
lithophile elements (RLE) in enstatite chondrites establish these meteorites as
the closest starting materials for the bulk of the silicate Earth and the core.
Comparing chondritic and terrestrial RLE ratios demonstrate that the Bulk
Silicate Earth, not the core, host the Earth's inventory of Ti, Zr, Nb, and Ta,
but not the full complement of V. | astro-ph_EP |
Mass transfer between debris discs during close stellar encounters: We study mass transfers between debris discs during stellar encounters. We
carried out numerical simulations of close flybys of two stars, one of which
has a disc of planetesimals represented by test particles. We explored the
parameter space of the encounters, varying the mass ratio of the two stars,
their pericentre and eccentricity of the encounter, and its geometry. We find
that particles are transferred to the other star from a restricted radial range
in the disc and the limiting radii of this transfer region depend on the
parameters of the encounter. We derive an approximate analytic description of
the inner radius of the region. The efficiency of the mass transfer generally
decreases with increasing encounter pericentre and increasing mass of the star
initially possessing the disc. Depending on the parameters of the encounter,
the transfer particles have a specific distributions in the space of orbital
elements (semimajor axis, eccentricity, inclination, and argument of
pericentre) around their new host star. The population of the transferred
particles can be used to constrain the encounter through which it was
delivered. We expect that many stars experienced transfer among their debris
discs and planetary systems in their birth environment. This mechanism presents
a formation channel for objects on wide orbits of arbitrary inclinations,
typically having high eccentricity but possibly also close-to-circular
(eccentricities of about 0.1). Depending on the geometry, such orbital elements
can be distinct from those of the objects formed around the star. | astro-ph_EP |
The architecture of multi-planet systems as a tracer of their formation
mechanisms: Exoplanets observed by the {\it Kepler} telescope exhibit a bi-modal, radius
distribution, which is known as the radius gap. We explore an origin of the
radius gap, focusing on multi-planet systems. Our simple theoretical argument
predicts that type I planetary migration produces different configurations of
protoplanets with different masses and such different configurations can result
in two distinguishable populations of small-sized multi-planet systems. We then
perform an observational analysis to verify this prediction. In the analysis,
multiple Kolmogorov-Smirnov tests are applied to the observed systems, using
the statistical measures that are devised to systematically characterize the
properties of multi-planet systems. We find with 99.5\% confidence that the
observed, small-sized multi-planet systems are divided into two distinct
populations. The distinction likely originates from different spatial
distributions of protoplanets, which are determined by type I migration and
subsequently trigger giant impact. We also show that these distinct populations
are separated around the radius gap when the gas surface density of
protoplanetary disks is $\sim 10^2$ g cm$^{-2}$ in the vicinity of the host
stars. This work therefore emphasizes the importance of planetary migration and
the inner disk properties. | astro-ph_EP |
Activity of (2060) Chiron possibly caused by impacts?: The centaur 95P/(2060) Chiron is showing comet-like activity since its
discovery, but the mass-loss mechanisms triggering its activity remained
unexplained. Although the collision rates in the centaur region are expected to
be very low, and impacts are thought not to be responsible for the mass-loss,
since the recent indications that Chiron might possess a ring similar to
Chariklo's, and assuming that there is debris orbiting around, the impact
triggered mass-loss mechanism should not be excluded as a possible cause of its
activity. From time series observations collected on Calar Alto Observatory in
Spain between 2014 and 2016, we found that the photometric scatter in Chiron's
data is larger than a control star's scatter, indicating a possible
microactivity, possibly caused by debris falling back to Chiron's surface and
lifting small clouds of material. We also present rotational light curves, and
measurements of Chiron's absolute magnitudes, that are consistent with the
models supporting the presumption that Chiron possesses rings. By co-adding the
images acquired in 2015, we have detected a $ \sim $5 arcsec long tail, showing
a surface brightness of 25.3 mag(V)/arcsec$^{2}$. | astro-ph_EP |
Inferring asymmetric limb cloudiness on exoplanets from transit light
curves: Clouds have been shown to be present in many exoplanetary atmospheres. Cloud
formation modeling predicts considerable inhomogeneities of cloud cover,
consistent with optical phase curve observations. However, optical phase curves
cannot resolve some existing degeneracies between cloud location and cloud
optical properties.
We present a conceptually simple technique to detect inhomogeneous cloud
cover on exoplanets. Such an inhomogeneous cloud cover produces an asymmetric
primary transit of the planet in front of the host star. Asymmetric transits
produce characteristic residuals compared to a standard symmetric model.
Furthermore, bisector spans can be used to determine asymmetries in the transit
light curve.
We apply a model of asymmetric transits to the light curves of HAT-P-7b,
Kepler-7b and HD209458b and search for possible cloud signatures. The nearly
uninterrupted Kepler photometry is particularly well-suited for this method
since it allows for a very high time resolution.
We do not find any statistically sound cloud signature in the data of the
considered planets. For HAT-P-7b, a tentative detection of an asymmetric cloud
cover is found, consistent with analysis of the optical phase curve. Based on
Bayesian probability arguments, a symmetric model with an offset in the transit
ephemeris remains, however, the most viable model. Still, this work
demonstrates that for suitable targets, namely low-gravity planets around
bright stars, the method can be used to constrain cloud cover characteristics
and is thus a helpful additional tool to study exoplanetary atmospheres. | astro-ph_EP |
Fractional Order Analysis of the Polytropic Models Applied to Exoplanets: Physical conditions deep within planets and exoplanets have yet to be
measured directly, but indirect methods can calculate them. The polytropic
models are one possible solution to this problem. In the present paper, we
assume that the interiors of planets follow a polytropic equation of state.
Hydrostatic equilibrium conditions are used to determine the overall structural
properties of the constituent matter. In the frame of the conformable
fractional derivatives, we use polytropic gas spheres to model the density
profiles, pressure profiles, temperature distributions, and the mass-radius
relations for the interiors of the initial stage of exoplanets. Planets of
single chemical composition were used to study the behavior of the mass-radius
relation, pressure distributions, and temperature distribution variation with
the fractional parameter. We calculated 72 fractional models for the mass of
protoplanets of 1MJ, 3MJ, and 10MJ (MJ is the mass of Jupiter), and the values
of the polytropic index are n=0, 0.5, 1, 1.5, and the fractional parameter rang
0.75-1. | astro-ph_EP |
IR Spectroscopy of Synthetic Glasses with Mercury Surface Composition:
Analogs for Remote Sensing: In a study to provide ground truth data for mid infrared observations of the
surface of Mercury with the MERTIS (Mercury Radiometer and Thermal Infrared
Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission, we have
studied 17 synthetic glasses. These samples have the chemical compositions of
characteristic Hermean surface areas based on MESSENGER data. The samples have
been characterized using optical microscopy, EMPA and Raman spectroscopy. Mid
infrared spectra have been obtained from polished thin sections using Micro
FTIR, and of powdered size fractions of bulk material (0-25, 25-63, 93-125 and
125-250 micron) in the 2.5 to 18 micron range. The synthetic glasses display
mostly spectra typical for amorphous materials with a dominating, single
Reststrahlen Band (RB) at 9.5 micron to 10.7 micron. RB Features of crystalline
forsterite are found in some cases at 9.5 to 10.2 micron, 10.4 to 11.2 micron,
and at 11.9 micron. Dendritic crystallization starts at a MgO content higher
than 23 wt.% MgO. The Reststrahlen Bands, Christiansen Features (CF), and
Transparency Features (TF) shift depending on the SiO2 and MgO contents. Also a
shift of the Christiansen Feature of the glasses compared with the SCFM
(SiO2/(SiO2+CaO+FeO+MgO)) index is observed. This shift could potentially help
distinguish crystalline and amorphous material in remote sensing data. A
comparison between the degree of polymerization of the glass and the width of
the characteristic strong silicate feature shows a weak positive correlation. A
comparison with a high-quality mid-IR spectrum of Mercury shows some moderate
similarity to the results of this study, but does not explain all features. | astro-ph_EP |
Absolute colours and phase coefficients of trans-Neptunian objects:
Correlations and Populations: The study of the visible colours of the trans-Neptunian objects opened a
discussion almost 20 years ago which, in spite of the increase in the amount of
available data, seems far from subside. Visible colours impose constraints to
the current theories of the early dynamical evolution of the Solar System such
as the environment of formation, initial surface composition, and how (if) they
were scattered to regions closer to the inner planets. In this paper we present
an updated version of our database of absolute colours and relative phase
coefficients for 117 objects. We define the absolute colours as the difference
of the absolute magnitudes $H_V-H_R$, and the relative phase coefficient as the
difference of the slopes of the phase curves $\Delta\beta$. These were obtained
joining our own observations plus data from the literature. The methodology has
been introduced in previous works and here we expand in some interesting
results, in particular the strong anti-correlation found between $H_V-H_R$ and
$\Delta\beta$, which means that redder objects have steeper phase curves in the
R filter, while bluer objects have steeper phase curves in the V filter. We
analyse a series of results published in the literature in view of our
database, which is free of phase effects, and show that their statistical
meaning is not very strong. We point out that phase-colouring and observational
errors play an important role in the understanding of these proposed
relationships. | astro-ph_EP |
Tidal Dissipation and Obliquity Evolution in Hot Jupiter Systems: Two formation scenarios have been proposed to explain the tight orbits of hot
Jupiters. They could be formed in orbits with a small inclination (with respect
to the stellar spin) via disk migration, or in more highly inclined orbits via
high-eccentricity migration, where gravitational interactions with a companion
and tidal dissipation are at play. Here we target hot Jupiter systems where the
misalignment $\lambda$ has been inferred observationally and we investigate
whether their properties are consistent with high-eccentricity migration.
Specifically, we study whether stellar tides can be responsible for the
observed distribution of $\lambda$ and orbital separations. Improving on
previous studies, we use detailed models for each star, thus accounting for how
convection (and tidal dissipation) depends on stellar properties. In line with
observations suggesting that hotter stars have higher $\lambda$, we find that
$\lambda$ increases as the amount of stellar surface convection decreases. This
trend supports the hypothesis that tides are the mechanism shaping the observed
distribution of $\lambda$. Furthermore, we study the past orbital evolution of
five representative systems, chosen to cover a variety of temperatures and
misalignments. We consider various initial orbital configurations and integrate
the equations describing the coupled evolution of the orbital separation,
stellar spin, and misalignment. We account for stellar tides and wind mass
loss, stellar evolution, and magnetic braking. We show that the current
properties of these five representative systems can be explained naturally,
given our current understanding of tidal dissipation and with physically
motivated assumptions for the effects driving the orbital evolution. | astro-ph_EP |
Understanding the atmospheric properties and chemical composition of the
ultra-hot Jupiter HAT-P-7b: III. Changing ionisation and the emergence of an
ionosphere: Ultra-hot Jupiters are the hottest close-in exoplanets discovered so far, and
present a unique possibility to explore hot and cold chemistry on one object.
The tidally locked ultra-hot Jupiter HAT-P-7b has a day/night temperature
difference of ~ 2500K, confining cloud formation to the nightside and efficient
ionisation to the dayside. Both have distinct observational signatures. We
analyse plasma and magnetic processes in the atmosphere of the ultra-hot
Jupiter HAT-P-7b to investigate the formation of a thermal ionosphere and the
possibility of magnetically coupling the atmospheric gas as the base for an
extended exosphere. We show which ions and atoms may be used as spectral
tracers, and if and where conditions for lightning may occur within the clouds
of HAT-P-7b, evaluate characteristic plasma and magnetic coupling parameters,
and a LTE radiative transfer is solved for the ionised gas phase. The
ionisation throughout HAT-P-7b's atmosphere varies drastically between day- and
nightside. The dayside has high levels of thermal ionisation and long-range
electromagnetic interactions dominate over kinetic electron-neutral
interactions, suggesting a day-night difference in magnetic coupling. K+, Na+,
Li+, Ca+, and Al+ are more abundant than their atomic counterparts on the
dayside. The minimum magnetic flux density for electrons for magnetic coupling
is B<0.5G for all regions of HAT-P-7b's atmosphere. HAT-P-7b's dayside has an
asymmetric ionosphere that extends deep into the atmosphere, the nightside has
no thermally driven ionosphere. A corresponding asymmetry is imprinted in the
ion/neutral composition at the terminators. The ionosphere on HAT-P-7b may be
directly traced by the Ca+ H&K lines if the local temperature is > 5000K. The
whole atmosphere may couple to a global, large-scale magnetic field, and
lightning may occur on the nightside. | astro-ph_EP |
The Architecture of the Cassini Division: The Cassini Division in Saturn's rings contains a series of eight named gaps,
three of which contain dense ringlets. Observations of stellar occultations by
the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft
have yielded ~40 accurate and precise measurements of the radial position of
the edges of all of these gaps and ringlets. These data reveal suggestive
patterns in the shapes of many of the gap edges: the outer edges of the 5 gaps
without ringlets are circular to within 1 km, while the inner edges of 6 of the
gaps are eccentric, with apsidal precession rates consistent with those
expected for eccentric orbits near each edge. Intriguingly, the pattern speeds
of these eccentric inner gap edges, together with that of the eccentric Huygens
ringlet,form a series with a characteristic spacing of 0.06 degrees/day. The
two gaps with non-eccentric inner edges lie near first-order Inner Lindblad
Resonances (ILRs) with moons. One such edge is close to the 5:4 ILR with
Prometheus. The other resonantly confined edge is the outer edge of the B ring,
which lies near the 2:1 Mimas ILR. Detailed investigation of the B-ring-edge
data confirm the presence of an m=2 perturbation on the B-ring edge, but also
suggest that this pattern moves or librates relative to Mimas. The B-ring edge
also has an m=1 component that rotates around the planet at a rate close to the
expected apsidal precession rate. The pattern speeds of the eccentric edges in
the Cassini Division can potentially be generated from various combinations of
the pattern speeds of structures observed on the edge of the B ring. We
therefore suggest that the locations of most of the gaps in the Cassini
Division may be determined by resonances involving a combination of
perturbations from Mimas and the massive edge of the B ring. | astro-ph_EP |
Hybrid methods in planetesimal dynamics (I) : Description of a new
composite algorithm: The formation and evolution of protoplanetary systems, the breeding grounds
of planet formation, is a complex dynamical problem that involves many orders
of magnitudes. To serve this purpose, we present a new hybrid algorithm that
combines a Fokker-Planck approach with the advantages of a pure
direct-summation N-body scheme, with a very accurate integration of close
encounters for the orbital evolution of the larger bodies with a statistical
model, envisaged to simulate the very large number of smaller planetesimals in
the disc. Direct-summation techniques have been historically developped for the
study of dense stellar systems such as open and globular clusters and, within
some limits imposed by the number of stars, of galactic nuclei. The number of
modifications to adapt direct-summation N-body techniques to planetary dynamics
is not undemanding and requires modifications. These include the way close
encounters are treated, as well as the selection process for the "neighbour
radius" of the particles and the extended Hermite scheme, used for the very
first time in this work, as well as the implementation of a central potential,
drag forces and the adjustment of the regularisation treatment. For the
statistical description of the planetesimal disc we employ a Fokker-Planck
approach. We include dynamical friction, high- and low-speed encounters, the
role of distant encounters as well as gas and collisional damping and then
generalise the model to inhomogenous discs. We then describe the combination of
the two techniques to address the whole problem of planetesimal dynamics in a
realistic way via a transition mass to integrate the evolution of the particles
according to their masses. | astro-ph_EP |
No hydrogen exosphere detected around the super-Earth HD97658 b: The exoplanet HD97658b provides a rare opportunity to probe the atmospheric
composition and evolution of moderately irradiated super-Earths. It transits a
bright K star at a moderate orbital distance of 0.08 au. Its low density is
compatible with a massive steam envelope that could photodissociate at high
altitudes and become observable as escaping hydrogen. Our analysis of 3
transits with HST/STIS at Ly-alpha reveals no such signature, suggesting that
the thermosphere is not hydrodynamically expanding and is subjected to a low
escape of neutral hydrogen (<10^8 g/s at 3 sigma). Using HST Ly-alpha and
Chandra & XMM-Newton observations at different epochs, we find that HD97658 is
a weak and soft X-ray source with signs of chromospheric variability in the
Ly-alpha line core. We determine an average reference for the intrinsic
Ly-alpha line and XUV spectrum of the star, and show that HD97658 b is in mild
conditions of irradiation compared to other known evaporating exoplanets with
an XUV irradiation about 3 times lower than the evaporating warm Neptune GJ436
b. This could be why the thermosphere of HD97658b is not expanding: the low XUV
irradiation prevents an efficient photodissociation of any putative steam
envelope. Alternatively, it could be linked to a low hydrogen content or
inefficient conversion of the stellar energy input. The HD97658 system provides
clues for understanding the stability of low-mass planet atmospheres. Our study
of HD97658 b can be seen as a control experiment of our methodology, confirming
that it does not bias detections of atmospheric escape and underlining its
strength and reliability. Our results show that stellar activity can be
efficiently discriminated from absorption signatures by a transiting exospheric
cloud. They also highlight the potential of observing the upper atmosphere of
small transiting planets to probe their physical and chemical properties | astro-ph_EP |
Disk Accretion Driven by Spiral Shocks: Spiral density waves are known to exist in many astrophysical disks,
potentially affecting disk structure and evolution. We conduct a numerical
study of the effects produced by a density wave, evolving into a shock, on the
characteristics of the underlying disk. We measure the deposition of angular
momentum in the disk by spiral shocks of different strength and verify the
analytical prediction of Rafikov (2016) for the behavior of this quantity,
using shock amplitude (which is potentially observable) as the input variable.
Good agreement between the theory and numerics is found as we vary shock
amplitude (including highly nonlinear shocks), disk aspect ratio, equation of
state, radial profiles of the background density and temperature, and pattern
speed of the wave. We show that high numerical resolution is required to
properly capture shock-driven transport, especially at low wave amplitudes. We
also demonstrate that relating local mass accretion rate to shock dissipation
in rapidly evolving disks requires accounting for the time-dependent
contribution to the angular momentum budget, caused by the time dependence of
the radial pressure support. We provide a simple analytical prescription for
the behavior of this contribution and demonstrate its excellent agreement with
the simulation results. Using these findings we formulate a theoretical
framework for studying one-dimensional (in radius) evolution of the
shock-mediated accretion disks, which can be applied to a variety of
astrophysical systems. | astro-ph_EP |
Kepler's Orbits and Special Relativity in Introductory Classical
Mechanics: Kepler's orbits with corrections due to Special Relativity are explored using
the Lagrangian formalism. A very simple model includes only relativistic
kinetic energy by defining a Lagrangian that is consistent with both the
relativistic momentum of Special Relativity and Newtonian gravity. The
corresponding equations of motion are solved in a Keplerian limit, resulting in
an approximate relativistic orbit equation that has the same form as that
derived from General Relativity in the same limit and clearly describes three
characteristics of relativistic Keplerian orbits: precession of perihelion;
reduced radius of circular orbit; and increased eccentricity. The prediction
for the rate of precession of perihelion is in agreement with established
calculations using only Special Relativity. All three characteristics are
qualitatively correct, though suppressed when compared to more accurate
general-relativistic calculations. This model is improved upon by including
relativistic gravitational potential energy. The resulting approximate
relativistic orbit equation has the same form and symmetry as that derived
using the very simple model, and more accurately describes characteristics of
relativistic orbits. For example, the prediction for the rate of precession of
perihelion of Mercury is one-third that derived from General Relativity. These
Lagrangian formulations of the special-relativistic Kepler problem are
equivalent to the familiar vector calculus formulations. In this Keplerian
limit, these models are supposed to be physical based on the likeness of the
equations of motion to those derived using General Relativity. The derivation
of this orbit equation is approachable by undergraduate physics majors and
nonspecialists whom have not had a course dedicated to relativity. | astro-ph_EP |
Evidence For A Vertical Dependence on the Pressure Structure in AS 209: We present an improved method to measure the rotation curves for disks with
non-axisymmetric brightness profiles initially published in Teague et al.
(2018a). Application of this method to the well studied AS$~$209 system shows
substantial deviations from Keplerian rotation of up to $\pm 5\%$. These
deviations are most likely due to perturbations in the gas pressure profile,
including a perturbation located at $\approx 250~$au and spanning up to
$\approx 50~$au which is only detected kinematically. Modelling the required
temperature and density profiles required to recover the observed rotation
curve we demonstrate that the rings observed in $\mu$m scattered light are
coincident with the pressure maxima, and are radially offset from the rings
observed in mm continuum emission. This suggests that if rings in the NIR are
due to sub-$\mu$m grains trapped in pressure maxima that there is a vertical
dependence on the radius of the pressure minima. | astro-ph_EP |
The Old and New Meanings of Cloud 'Belt' and 'Zone': A Study of Jovian
and Saturnian Atmospheric Banding: The brightness of cloud bands on Jupiter and Saturn as a function of latitude
is reported. Bright Jovian bands near the equator are located in regions of
anti-cyclonic circulation of the atmosphere. By contrast, bright equatorial
bands on Saturn are associated with cyclonic motion. Modern definitions of the
cloud band terms 'zone' and 'belt' are distinguished from their old meanings. | astro-ph_EP |
Extreme trans-Neptunian objects and the Kozai mechanism: signalling the
presence of trans-Plutonian planets: The existence of an outer planet beyond Pluto has been a matter of debate for
decades and the recent discovery of 2012 VP113 has just revived the interest
for this controversial topic. This Sedna-like object has the most distant
perihelion of any known minor planet and the value of its argument of
perihelion is close to 0 degrees. This property appears to be shared by almost
all known asteroids with semimajor axis greater than 150 au and perihelion
greater than 30 au (the extreme trans-Neptunian objects or ETNOs), and this
fact has been interpreted as evidence for the existence of a super-Earth at 250
au. In this scenario, a population of stable asteroids may be shepherded by a
distant, undiscovered planet larger than the Earth that keeps the value of
their argument of perihelion librating around 0 degrees as a result of the
Kozai mechanism. Here, we study the visibility of these ETNOs and confirm that
the observed excess of objects reaching perihelion near the ascending node
cannot be explained in terms of any observational biases. This excess must be a
true feature of this population and its possible origin is explored in the
framework of the Kozai effect. The analysis of several possible scenarios
strongly suggest that at least two trans-Plutonian planets must exist. | astro-ph_EP |
The Manifold Of Variations: impact location of short-term impactors: The interest in the problem of small asteroids observed shortly before a deep
close approach or an impact with the Earth has grown a lot in recent years.
Since the observational dataset of such objects is very limited, they deserve
dedicated orbit determination and hazard assessment methods. The currently
available systems are based on the systematic ranging, a technique providing a
2-dimensional manifold of orbits compatible with the observations, the
so-called Manifold Of Variations. In this paper we first review the Manifold Of
Variations method, to then show how this set of virtual asteroids can be used
to predict the impact location of short-term impactors, and compare the results
with those of already existent methods. | astro-ph_EP |
Determining fireball fates using the $α$-$β$ criterion: As fireball networks grow, the number of events observed becomes unfeasible
to manage by manual efforts. Reducing and analysing big data requires automated
data pipelines. Triangulation of a fireball trajectory can swiftly provide
information on positions and, with timing information, velocities. However,
extending this pipeline to determine the terminal mass estimate of a meteoroid
is a complex next step. Established methods typically require assumptions to be
made of the physical meteoroid characteristics (such as shape and bulk
density). To determine which meteoroids may have survived entry there are
empirical criteria that use a fireball's final height and velocity - low and
slow final parameters are likely the best candidates. We review the more
elegant approach of the dimensionless coefficient method. Two parameters,
$\alpha$ (ballistic coefficient) and $\beta$ (mass-loss), can be calculated for
any event with some degree of deceleration, given only velocity and height
information. $\alpha$ and $\beta$ can be used to analytically describe a
trajectory with the advantage that they are not mere fitting coefficients; they
also represent the physical meteoroid properties. This approach can be applied
to any fireball network as an initial identification of key events and
determine on which to concentrate resources for more in depth analyses. We used
a set of 278 events observed by the Desert Fireball Network to show how
visualisation in an $\alpha$ - $\beta$ diagram can quickly identify which
fireballs are likely meteorite candidates. | astro-ph_EP |
A Possible Mechanism for Overcoming the Electrostatic Barrier Against
Dust Growth in Protoplanetary disks: The coagulation of dust particles under the conditions in protoplanetary
disks is investigated. The study focuses on the repulsive electrostatic barrier
against growth of charged dust grains. Taking into account the photoelectric
effect leads to the appearance of a layer at intermediate heights where the
dust has a close to zero charge, enabling the dust grains to grow efficiently.
An increase in the coagulation rate comes about not only due to the lowering of
the Coulomb barrier, but also because of the electrostatic attraction between
grains of opposite charge due to the non-zero dispersion of the near-zero
charge. Depending on the efficiency of mixing in the disk, the acceleration of
the evolution of the dust in this layer could be important, both in the
quasi-stationary stage of the disk evolution and during its dispersal. | astro-ph_EP |
Lightcurve Survey of V-type Asteroids. I. Observations until Spring 2004: To examine the distribution of rotational rates for chips of asteroid 4
Vesta, lightcurve observation of seven V-type asteroids (2511 Patterson, 2640
Hallstorm, 2653 Principia, 2795 Lapage, 3307 Athabasca, 4147 Lennon, and 4977
Rauthgundis) were performed from fall 2003 to spring 2004. Distribution of spin
rates of V-type main-belt asteroids from the past and our observations have
three peaks. This result implies that age of catastrophic impact making Vesta
family may be not as young as Karin and Iannini families but as old as Eos and
Koronis families. | astro-ph_EP |
Precise Dynamical Masses and Orbital Fits for $β$ Pic b and $β$
Pic c: We present a comprehensive orbital analysis to the exoplanets $\beta$
Pictoris b and c that resolves previously reported tensions between the
dynamical and evolutionary mass constraints on $\beta$ Pic b. We use the MCMC
orbit code orvara to fit fifteen years of radial velocities and relative
astrometry (including recent GRAVITY measurements), absolute astrometry from
Hipparcos and Gaia, and a single relative radial velocity measurement between
$\beta$ Pic A and b. We measure model-independent masses of
$9.3^{+2.6}_{-2.5}\, M_{\rm Jup}$ for $\beta$ Pic b and $8.3\pm 1.0\,M_{\rm
Jup}$ for $\beta$ Pic c. These masses are robust to modest changes to the input
data selection. We find a well-constrained eccentricity of $0.119 \pm 0.008$
for $\beta$ Pic b, and an eccentricity of $0.21^{+0.16}_{-0.09}$ for $\beta$
Pic c, with the two orbital planes aligned to within $\sim$0.5$^\circ$. Both
planets' masses are within $\sim$1$\sigma$ of the predictions of hot-start
evolutionary models and exclude cold starts. We validate our approach on
$N$-body synthetic data integrated using REBOUND. We show that orvara can
account for three-body effects in the $\beta$ Pic system down to a level
$\sim$5 times smaller than the GRAVITY uncertainties. Systematics in the masses
and orbital parameters from orvara's approximate treatment of multiplanet
orbits are a factor of $\sim$5 smaller than the uncertainties we derive here.
Future GRAVITY observations will improve the constraints on $\beta$ Pic c's
mass and (especially) eccentricity, but improved constraints on the mass of
$\beta$ Pic b will likely require years of additional RV monitoring and
improved precision from future Gaia data releases. | astro-ph_EP |
Detecting extrasolar moons akin to solar system satellites with an
orbital sampling effect: Despite years of high accuracy observations, none of the available
theoretical techniques has yet allowed the confirmation of a moon beyond the
solar system. Methods are currently limited to masses about an order of
magnitude higher than the mass of any moon in the solar system. I here present
a new method sensitive to exomoons similar to the known moons. Due to the
projection of transiting exomoon orbits onto the celestial plane, satellites
appear more often at larger separations from their planet. After about a dozen
randomly sampled observations, a photometric orbital sampling effect (OSE)
starts to appear in the phase-folded transit light curve, indicative of the
moons' radii and planetary distances. Two additional outcomes of the OSE emerge
in the planet's transit timing variations (TTV-OSE) and transit duration
variations (TDV-OSE), both of which permit measurements of a moon's mass. The
OSE is the first effect that permits characterization of multi-satellite
systems. I derive and apply analytical OSE descriptions to simulated transit
observations of the Kepler space telescope assuming white noise only. Moons as
small as Ganymede may be detectable in the available data, with M stars being
their most promising hosts. Exomoons with the 10-fold mass of Ganymede and a
similar composition (about 0.86 Earth radii in radius) can most likely be found
in the available Kepler data of K stars, including moons in the stellar
habitable zone. A future survey with Kepler-class photometry, such as Plato
2.0, and a permanent monitoring of a single field of view over 5 years or more
will very likely discover extrasolar moons via their OSEs. | astro-ph_EP |
Probing exoplanet clouds with optical phase curves: Kepler-7b is to date the only exoplanet for which clouds have been inferred
from the optical phase curve -- from visible-wavelength whole-disk brightness
measurements as a function of orbital phase. Added to this, the fact that the
phase curve appears dominated by reflected starlight makes this close-in giant
planet a unique study case. Here we investigate the information on coverage and
optical properties of the planet clouds contained in the measured phase curve.
We generate cloud maps of Kepler-7b and use a multiple-scattering approach to
create synthetic phase curves, thus connecting postulated clouds with
measurements. We show that optical phase curves can help constrain the
composition and size of the cloud particles. Indeed, model fitting for
Kepler-7b requires poorly absorbing particles that scatter with low-to-moderate
anisotropic efficiency, conclusions consistent with condensates of silicates,
perovskite, and silica of submicron radii. We also show that we are limited in
our ability to pin down the extent and location of the clouds. These
considerations are relevant to the interpretation of optical phase curves with
general circulation models. Finally, we estimate that the spherical albedo of
Kepler-7b over the Kepler passband is in the range 0.4--0.5. | astro-ph_EP |
Photoevaporative Dispersal of Protoplanetary Disks around Evolving
Intermediate-mass Stars: We aim to understand the effect of stellar evolution on the evolution of
protoplanetary disks. We focus in particular on the disk evolution around
intermediate-mass (IM) stars, which evolve more rapidly than low-mass ones. We
numerically solve the long-term evolution of disks around 0.5-5 solar-mass
stars considering viscous accretion and photoevaporation (PE) driven by stellar
far-ultraviolet (FUV), extreme-ultraviolet (EUV), and X-ray emission. We also
take stellar evolution into account and consider the time evolution of the PE
rate. We find that the FUV, EUV, and X-ray luminosities of IM stars evolve by
orders of magnitude within a few Myr along with the time evolution of stellar
structure, stellar effective temperature, or accretion rate. Therefore, the PE
rate also evolves with time by orders of magnitude, and we conclude that
stellar evolution is crucial for the disk evolution around IM stars. | astro-ph_EP |
Spectroscopic Time-series Performance of JWST/NIRSpec from Commissioning
Observations: We report on JWST commissioning observations of the transiting exoplanet
HAT-P-14 b, obtained using the Bright Object Time Series (BOTS) mode of the
NIRSpec instrument with the G395H/F290LP grating/filter combination
($3-5\mu$m). While the data were used primarily to verify that the NIRSpec BOTS
mode is working as expected, and to enable it for general scientific use, they
yield a precise transmission spectrum which we find is featureless down to the
precision level of the instrument, consistent with expectations given
HAT-P-14~b's small scale-height and hence expected atmospheric features. The
exquisite quality and stability of the \emph{JWST/NIRSpec} transit spectrum --
almost devoid of any systematic effects -- allowed us to obtain median
uncertainties of 50-60 ppm in this wavelength range at a resolution of $R=100$
in a single exposure, which is in excellent agreement with pre-flight
expectations and close to the (or at the) photon-noise limit for a $J = 9.094$,
F-type star like HAT-P-14. These observations showcase the ability of
NIRSpec/BOTS to perform cutting-edge transiting exoplanet atmospheric science,
setting the stage for observations and discoveries to be made in Cycle 1 and
beyond. | astro-ph_EP |
Structured Distributions of Gas and Solids in Protoplanetary Disks: Recent spatially-resolved observations of protoplanetary disks revealed a
plethora of substructures, including concentric rings and gaps, inner cavities,
misalignments, spiral arms, and azimuthal asymmetries. This is the major
breakthrough in studies of protoplanetary disks since Protostars and Planets VI
and is reshaping the field of planet formation. However, while the capability
of imaging substructures in protoplanetary disks has been steadily improving,
the origin of many substructures are still largely debated. The structured
distributions of gas and solids in protoplanetary disks likely reflect the
outcome of physical processes at work, including the formation of planets. Yet,
the diverse properties among the observed protoplanetary disk population, for
example, the number and radial location of rings and gaps in the dust
distribution, suggest that the controlling process may differ between disks
and/or the outcome may be sensitive to stellar or disk properties. In this
review, we (1) summarize the existing observations of protoplanetary disk
substructures collected from the literature; (2) provide a comprehensive
theoretical review of various processes proposed to explain observed
protoplanetary disk substructures; (3) compare current theoretical predictions
with existing observations and highlight future research directions to
distinguish between different origins; and (4) discuss implications of
state-of-the-art protoplanetary disk observations to protoplanetary disk and
planet formation theory. | astro-ph_EP |
Thermal properties of Rhea's Poles: Evidence for a Meter-Deep
Unconsolidated Subsurface Layer: Cassini's Composite Infrared Spectrometer (CIRS) observed both of Rhea's
polar regions during two flybys on 2013/03/09 and 2015/02/10. The results show
Rhea's southern winter pole is one of the coldest places directly observed in
our solar system: temperatures of 25.4+/-7.4 K and 24.7+/-6.8 K are inferred.
The surface temperature of the northern summer pole is warmer: 66.6+/-0.6 K.
Assuming the surface thermophysical properties of both polar regions are
comparable then these temperatures can be considered a summer and winter
seasonal temperature constraint for the polar region. These observations
provide solar longitude coverage at 133 deg and 313 deg for the summer and
winter poles respectively, with additional winter temperature constraint at 337
deg. Seasonal models with bolometric albedos of 0.70-0.74 and thermal inertias
of 1-46 MKS can provide adequate fits to these temperature constraints. Both
these albedo and thermal inertia values agree (within error) with those
previously observed on both Rhea's leading and trailing hemispheres.
Investigating the seasonal temperature change of Rhea's surface is particularly
important, as the seasonal wave is sensitive to deeper surface temperatures
(~10cm to m) than the more commonly reported diurnal wave (<1cm). The low
thermal inertia derived here implies that Rhea's polar surfaces are highly
porous even at great depths. Analysis of a CIRS 10 to 600 cm-1 stare
observation, taken between 16:22:33 and 16:23:26 UT on 2013/03/09 centered on
71.7 W, 58.7 S provides the first analysis of a thermal emissivity spectrum on
Rhea. The results show a flat emissivity spectrum with negligible emissivity
features. A few possible explanations exist for this flat emissivity spectrum,
but the most likely for Rhea is that the surface is both highly porous and
composed of small particles (less than approximately 50 um). | astro-ph_EP |
A Planetary Companion around a Metal-Poor Star with Extragalactic Origin: We report the detection of a planetary companion around HIP 13044, a
metal-poor star on the red Horizontal Branch. The detection is based on radial
velocity observations with FEROS, a high-resolution spectrograph at the 2.2-m
MPG/ESO telescope, located at ESO La Silla observatory in Chile. The periodic
radial velocity variation of P = 16.2 days can be distinguished from the
periods of the stellar activity indicators. We computed a minimum planetary
mass of 1.25 MJup and an orbital semi-major axis of 0.116 AU for the planet.
This discovery is unique in three aspects: First, it is the first planet
detection around a star with a metallicity much lower than few percent of the
solar value; second, the planet host star resides in a stellar evolutionary
stage that is still unexplored in the exoplanet surveys; third, the star HIP
13044 belongs to one of the most significant stellar halo streams in the solar
neighborhood, implying an extragalactic origin of the planetary system HIP
13044 in a disrupted former satellite of the Milky Way. | astro-ph_EP |
New transit timing observations for GJ 436 b, HAT-P-3 b, HAT-P-19 b,
WASP-3 b, and XO-2 b: We present new transit observations acquired between 2014 and 2018 for the
hot exoplanets GJ 436 b, HAT-P-3 b, HAT-P-19 b, WASP-3 b, and XO-2 b. New
mid-transit times extend the timespan covered by observations of these
exoplanets and allow us to refine their transit ephemerides. All new transits
are consistent with linear ephemerides. | astro-ph_EP |
Autonomous Rapid Exploration in Close-Proximity of an Asteroid: The increasing number of space missions may overwhelm ground support
infrastructure, prompting the need for autonomous deep-space guidance,
navigation, and control (GN\&C) systems. These systems offer sustainable and
cost-effective solutions, particularly for asteroid missions that deal with
uncertain environments. This study proposes a paradigm shift from the proposals
currently found in the literature for autonomous asteroid exploration, which
inherit the conservative architecture from the ground-in-the-loop approach that
relies heavily on reducing uncertainties before close-proximity operations.
Instead, it advocates for robust guidance and control to handle uncertainties
directly, without extensive navigation campaigns. From a series of conservative
assumptions, we demonstrate the feasibility of this autonomous GN\&C for
robotic spacecraft by using existing technology. It is shown that a bolder
operational approach enables autonomous spacecraft to significantly reduce
exploration time by weeks or months. This paradigm shift holds great potential
for reducing costs and saving time in autonomous missions of the future. | astro-ph_EP |
Planet Shadows in Protoplanetary Disks. II: Observable Signatures: We calculate simulated images of disks perturbed by embedded small planets.
These 10-50 M_Earth bodies represent the growing cores of giant planets. We
examine scattered light and thermal emission from these disks over a range of
wavelengths, taking into account the wavelength-dependent opacity of dust in
the disk. We also examine the effect of inclination on the observed
perturbations. We find that the perturbations are best observed in the visible
to mid-infrared. Scattered light images reflect shadows produced at the surface
of perturbed disks, while the infrared images follow thermal emission from the
surface of the disk, showing cooled/heated material in the shadowed/brightened
regions. At still longer wavelengths in the sub-millimeter, the perturbation
fades as the disk becomes optically thin and surface features become
overwhelmed by emission closer toward the midplane of the disk. With the
construction of telescopes such as TMT, GMT and ALMA due in the next decade,
there is a real possibility of observing planets forming in disks in the
optical and sub-millimeter. However, having the angular resolution to observe
the features in the mid-infrared will remain a challenge. | astro-ph_EP |
Kepler-1656b's Extreme Eccentricity: Signature of a Gentle Giant: Highly eccentric orbits are one of the major surprises of exoplanets relative
to the Solar System and indicate rich and tumultuous dynamical histories. One
system of particular interest is Kepler-1656, which hosts a sub-Jovian planet
with an eccentricity of 0.8. Sufficiently eccentric orbits will shrink in
semi-major axis due to tidal dissipation of orbital energy during periastron
passage. Here our goal was to assess whether Kepler-1656b is currently
undergoing such high-eccentricity migration, and to further understand the
system's origins and architecture. We confirm a second planet in the system
with $M_{\rm c}= 0.40 \pm 0.09M_{\rm jup}$ and P$_{\rm c}= 1919\pm 27\,$days.
We simulated the dynamical evolution of planet b in the presence of planet c
and find a variety of possible outcomes for the system, such as tidal migration
and engulfment. The system is consistent with an in situ dynamical origin of
planet b followed by subsequent Eccentric Kozai Lidov (EKL) perturbations that
excite Kepler-1656b's eccentricity gently, i.e. without initiating tidal
migration. Thus, despite its high eccentricity, we find no evidence that planet
b is or has migrated through the high-eccentricity channel. Finally, we predict
the outer orbit to be mutually inclined in a nearly perpendicular configuration
with respect to the inner planet orbit based on the outcomes of our
simulations, and make observable predictions for the inner planet's spin-orbit
angle. Our methodology can be applied to other eccentric or tidally locked
planets to constrain their origins, orbital configurations and properties of a
potential companion. | astro-ph_EP |
Spectral signature of atmospheric winds in high resolution transit
observations: The study of exoplanet atmospheres showed large diversity compared to the
planets in our solar system. Especially Jupiter type exoplanets orbiting their
host star in close orbits, the so-called hot and ultra-hot Jupiters, have been
studied in detail due to their enhanced atmospheric signature. Due to their
tidally locked status, the temperature difference between the day- and
nightside triggers atmospheric winds which can lead to various fingerprints in
the observations. Spatially resolved absorption lines during transit such as
sodium (Na) could be a good tracer for such winds. Different works resolved the
Na$^-$ absorption lines on different exoplanets which show different line
widths. Assuming that this could be attributed to such zonal jet streams, this
work models the effect of such winds on synthetic absorption lines. For this,
transiting Jupiter type planets with rotational velocities similar to hot and
ultra-hot Jupiter are considered. The investigation shows that high wind
velocities could reproduce the broadening of Na-line profiles inferred in
different high-resolution transit observations. There is a tendency that the
broadening values decrease for planets with lower equilibrium temperature. This
could be explained by atmospheric drag induced by the ionization of alkali
lines which slow down the zonal jet streams, favoring their existence on hot
Jupiter rather than ultra-hot Jupiter. | astro-ph_EP |
Possible formation pathways for the low density Neptune-mass planet
HAT-P-26b: We investigate possible pathways for the formation of the low density
Neptune-mass planet HAT-P-26b. We use two formation different models based on
pebbles and planetesimals accretion, and includes gas accretion, disk migration
and simple photoevaporation. The models tracks the atmospheric oxygen
abundance, in addition to the orbital period, and mass of the forming planets,
that we compare to HAT-P-26b. We find that pebbles accretion can explain this
planet more naturally than planetesimals accretion that fails completely unless
we artificially enhance the disk metallicity significantly. Pebble accretion
models can reproduce HAT-P-26b with either a high initial core mass and low
amount of envelope enrichment through core erosion or pebbles dissolution, or
the opposite, with both scenarios being possible. Assuming a low envelope
enrichment factor as expected from convection theory and comparable to the
values we can infer from the D/H measurements in Uranus and Neptune, our most
probable formation pathway for HAT-P-26b is through pebble accretion starting
around 10 AU early in the disk's lifetime. | astro-ph_EP |
Stochastic orbital migration of small bodies in Saturn's rings: Many small moonlets, creating propeller structures, have been found in
Saturn's rings by the Cassini spacecraft. We study the dynamical evolution of
such 20-50m sized bodies which are embedded in Saturn's rings. We estimate the
importance of various interaction processes with the ring particles on the
moonlet's eccentricity and semi-major axis analytically. For low ring surface
densities, the main effects on the evolution of the eccentricity and the
semi-major axis are found to be due to collisions and the gravitational
interaction with particles in the vicinity of the moonlet. For large surface
densities, the gravitational interaction with self-gravitating wakes becomes
important.
We also perform realistic three dimensional, collisional N-body simulations
with up to a quarter of a million particles. A new set of pseudo shear periodic
boundary conditions is used which reduces the computational costs by an order
of magnitude compared to previous studies. Our analytic estimates are confirmed
to within a factor of two.
On short timescales the evolution is always dominated by stochastic effects
caused by collisions and gravitational interaction with self-gravitating ring
particles. These result in a random walk of the moonlet's semi-major axis. The
eccentricity of the moonlet quickly reaches an equilibrium value due to
collisional damping. The average change in semi-major axis of the moonlet after
100 orbital periods is 10-100m. This translates to an offset in the azimuthal
direction of several hundred kilometres. We expect that such a shift is easily
observable. | astro-ph_EP |
Vortex Formation and Survival in Protoplanetary Disks subject to
Vertical Shear Instability: Several protoplanetary disks observed by ALMA show dust concentrations
consistent with particle trapping in giant vortices. The formation and survival
of vortices is of major importance for planet formation, because vortices act
as particle traps and are therefore preferred locations of planetesimal
formation. Recent studies showed that the vertical shear instability (VSI) is
capable of generating turbulence and small vortices in protoplanetary disks
that have the proper radial and vertical stratification and thermally relax on
sufficiently short time scales. But the effect of the azimuthal extend of the
disk is often neglected as the disks azimuth is limited to $\Delta \phi \leq
\pi/2$. We aim to investigate the influence of the azimuthal extent of the disk
on the long-term evolution of a protoplanetary disk and the possibility of
large vortices forming. To this end, we perform 3-dimensional simulations for
up to 1000 local orbits using different values of $\Delta \phi = \pi/2 $ to
$2\pi$ for VSI in disks with a prescribed radial density and temperature
gradient cooling on short timescales. We find the VSI capable of forming large
vortices which can exist at least several hundred orbits in simulations
covering a disk with $\Delta \phi \geq \pi$. This suggests the VSI to be
capable to form vortices or at least to trigger vortex formation via a
secondary instability, e.g. Rossby Wave Instability or Kelvin Helmholtz
Instability. | astro-ph_EP |
Orbital structure of the GJ876 extrasolar planetary system, based on the
latest Keck and HARPS radial velocity data: We use full available array of radial velocity data, including recently
published HARPS and Keck observatory sets, to characterize the orbital
configuration of the planetary system orbiting GJ876. First, we propose and
describe in detail a fast method to fit perturbed orbital configuration, based
on the integration of the sensitivity equations inferred by the equations of
the original $N$-body problem. Further, we find that it is unsatisfactory to
treat the available radial velocity data for GJ876 in the traditional white
noise model, because the actual noise appears autocorrelated (and demonstrates
non-white frequency spectrum). The time scale of this correlation is about a
few days, and the contribution of the correlated noise is about 2 m/s (i.e.,
similar to the level of internal errors in the Keck data). We propose a
variation of the maximum-likelihood algorithm to estimate the orbital
configuration of the system, taking into account the red noise effects. We
show, in particular, that the non-zero orbital eccentricity of the innermost
planet \emph{d}, obtained in previous studies, is likely a result of
misinterpreted red noise in the data. In addition to offsets in some orbital
parameters, the red noise also makes the fit uncertainties systematically
underestimated (while they are treated in the traditional white noise model).
Also, we show that the orbital eccentricity of the outermost planet is actually
ill-determined, although bounded by $\sim 0.2$. Finally, we investigate
possible orbital non-coplanarity of the system, and limit the mutual
inclination between the planets \emph{b} and \emph{c} orbits by
$5^\circ-15^\circ$, depending on the angular position of the mutual orbital
nodes. | astro-ph_EP |
Radial Drift of Dust in Protoplanetary Disks: The Evolution of Ice lines
and Dead zones: We have developed a new model for the astrochemical structure of a viscously
evolving protoplanetary disk that couples an analytic description of the disk's
temperature and density profile, chemical evolution, and an evolving dust
distribution. We compute evolving radial distributions for a range of dust
grain sizes, which depend on coagulation, fragmentation and radial drift
processes. In particular we find that the water ice line plays an important
role in shaping the radial distribution of the maximum grain size because ice
coated grains are significantly less susceptible to fragmentation than their
dry counterparts. This in turn has important effects on disk ionization and
therefore on the location of dead zones. In comparison to a simple constant
gas-to-dust ratio model for the dust as an example, we find that the new model
predicts an outer dead zone edge that moves in by a factor of about 3 at 1 Myr
(to 5 AU) and by a factor of about 14 by 3 Myr (to 0.5 AU). We show that the
changing position of the dead zone and heat transition traps have important
implications for the formation and trapping of planets in protoplanetary disks.
Finally, we consider our results in light of recent ALMA observations of HL Tau
and TW Hya. | astro-ph_EP |
Effect of Non-Adiabatic Thermal Profiles on the Inferred Compositions of
Uranus and Neptune: It has been a common assumption of interior models that the outer planets of
our solar system are convective, and that the internal temperature
distributions are therefore adiabatic. This assumption is also often applied to
exoplanets. However, if a large portion of the thermal flux can be transferred
by conduction, or if convection is inhibited, the thermal profile could be
substantially different and would therefore affect the inferred planetary
composition. Here we investigate how the assumption of non-adiabatic
temperature profiles in Uranus and Neptune affects their internal structures
and compositions. We use a set of plausible temperature profiles together with
density profiles that match the measured gravitational fields to derive the
planets' compositions. We find that the inferred compositions of both Uranus
and Neptune are quite sensitive to the assumed thermal profile in the outer
layers, but relatively insensitive to the thermal profile in the central, high
pressure region. The overall value of the heavy element mass fraction, $Z$, for
these planets is between 0.8 and 0.9. Finally, we suggest that large parts of
Uranus' interior might be conductive, a conclusion that is consistent with
Uranus dynamo models and a hot central inner region. | astro-ph_EP |
Predicting the magnetic vectors within coronal mass ejections arriving
at Earth: 1. Initial Architecture: The process by which the Sun affects the terrestrial environment on short
timescales is predominately driven by the amount of magnetic reconnection
between the solar wind and Earth's magnetosphere. Reconnection occurs most
efficiently when the solar wind magnetic field has a southward component. The
most severe impacts are during the arrival of a coronal mass ejection (CME)
when the magnetosphere is both compressed and magnetically connected to the
heliospheric environment. Unfortunately, forecasting magnetic vectors within
coronal mass ejections remains elusive. Here we report how, by combining a
statistically robust helicity rule for a CME's solar origin with a simplified
flux rope topology the magnetic vectors within the Earth-directed segment of a
CME can be predicted. In order to test the validity of this proof-of-concept
architecture for estimating the magnetic vectors within CMEs, a total of eight
CME events (between 2010 and 2014) have been investigated. With a focus on the
large false alarm of January 2014, this work highlights the importance of
including the early evolutionary effects of a CME for forecasting purposes. The
angular rotation in the predicted magnetic field closely follows the broad
rotational structure seen within the in situ data. This time-varying field
estimate is implemented into a process to quantitatively predict a time-varying
Kp index that is described in detail in paper II. Future statistical work,
quantifying the uncertainties in this process, may improve the more heuristic
approach used by early forecasting systems. | astro-ph_EP |
Ground- and Space-based Detection of the Thermal Emission Spectrum of
the Transiting Hot Jupiter KELT-2Ab: We describe the detection of water vapor in the atmosphere of the transiting
hot Jupiter KELT-2Ab by treating the star-planet system as a spectroscopic
binary with high-resolution, ground-based spectroscopy. We resolve the signal
of the planet's motion with deep combined flux observations of the star and the
planet. In total, six epochs of Keck NIRSPEC $L$-band observations were
obtained, and the full data set was subjected to a cross correlation analysis
with a grid of self-consistent atmospheric models. We measure a radial
projection of the Keplerian velocity, $K_P$, of 148 $\pm$ 7 km s$^{-1}$,
consistent with transit measurements, and detect water vapor at 3.8$\sigma$. We
combine NIRSPEC $L$-band data with $Spitzer$ IRAC secondary eclipse data to
further probe the metallicity and carbon-to-oxygen ratio of KELT-2Ab's
atmosphere. While the NIRSPEC analysis provides few extra constraints on the
$Spitzer$ data, it does provide roughly the same constraints on metallicity and
carbon-to-oxygen ratio. This bodes well for future investigations of the
atmospheres of non-transiting hot Jupiters. | astro-ph_EP |
Multi-Output Random Forest Regression to Emulate the Earliest Stages of
Planet Formation: In the current paradigm of planet formation research, it is believed that the
first step to forming massive bodies (such as asteroids and planets) requires
that small interstellar dust grains floating through space collide with each
other and grow to larger sizes. The initial formation of these pebbles is
governed by an integro-differential equation known as the Smoluchowski
coagulation equation, to which analytical solutions are intractable for all but
the simplest possible scenarios. While brute-force methods of approximation
have been developed, they are computationally costly, currently making it
infeasible to simulate this process including other physical processes relevant
to planet formation, and across the very large range of scales on which it
occurs. In this paper, we take a machine learning approach to designing a
system for a much faster approximation. We develop a multi-output random forest
regression model trained on brute-force simulation data to approximate
distributions of dust particle sizes in protoplanetary disks at different
points in time. The performance of our random forest model is measured against
the existing brute-force models, which are the standard for realistic
simulations. Results indicate that the random forest model can generate highly
accurate predictions relative to the brute-force simulation results, with an
$R^{2}$ of 0.97, and do so significantly faster than brute-force methods. | astro-ph_EP |
Concentrating small particles in protoplanetary disks through the
streaming instability: Laboratory experiments indicate that direct growth of silicate grains via
mutual collisions can only produce particles up to roughly millimeters in size.
On the other hand, recent simulations of the streaming instability have shown
that mm/cm-sized particles require an excessively high metallicity for dense
filaments to emerge. Using a numerical algorithm for stiff mutual drag force,
we perform simulations of small particles with significantly higher resolutions
and longer simulation times than in previous investigations. We find that
particles of dimensionless stopping time $\tau_\mathrm{s} = 10^{-2}$ and
$10^{-3}$ -- representing mm- and cm-sized particles interior of the water ice
line -- concentrate themselves via the streaming instability at a solid
abundance of a few percent. We thus revise a previously published critical
solid abundance curve for the regime of $\tau_\mathrm{s} \ll 1$. The solid
density in the concentrated regions reaches values higher than the Roche
density, indicating that direct collapse of particles down to mm sizes into
planetesimals is possible. Our results hence bridge the gap in particle size
between direct dust growth limited by bouncing and the streaming instability. | astro-ph_EP |
KIC 8462852: Transit of a Large Comet Family: We investigate the plausibility of a cometary source of the unusual transits
observed in the KIC 8462852 light curve. A single comet of similar size to
those in our solar system produces a transit depth of the order of $10^{-3}$
lasting less than a day which is much smaller and shorter than the largest dip
observed ($\sim20\%$ for $\sim3$ days), but a large, closely traveling cluster
of comets can fit the observed depths and durations. We find that a series of
large comet swarms, with all but one on the same orbit, provides a good fit for
the KIC 8462852 data during Quarters 16 and 17, but does not explain the large
dip observed during Quarter 8. However, the transit dips only loosely constrain
the orbits and can be fit by swarms with periastrons differing by a factor of
10. To reach a transit depth of $\sim0.2$, the comets need to be in a close
group of $\sim30$, if they are $\sim100$ km in radius or in a group of
$\sim300$ if they are $\sim10$ km in radius. The total number of comets
required to fit all of the dips is $\sim70$ $\sim$100 km or $\sim700$ $\sim10$
km comets. A single comet family from a tidally disrupted Ceres-sized
progenitor or the start of a Late Heavy Bombardment period explains the last
$\sim60$ days of the unusual KIC 8462852 light curve. | astro-ph_EP |
A grid of upper atmosphere models for 1--40 MEARTH planets: application
to CoRoT-7 b and HD219134 b,c: There is growing observational and theoretical evidence suggesting that
atmospheric escape is a key driver of planetary evolution. Commonly, planetary
evolution models employ simple analytic formulae (e.g., energy limited escape)
that are often inaccurate, and more detailed physical models of atmospheric
loss usually only give snapshots of an atmosphere's structure and are difficult
to use for evolutionary studies. To overcome this problem, we upgrade and
employ an already existing upper atmosphere hydrodynamic code to produce a
large grid of about 7000 models covering planets with masses 1 - 39 Earth mass
with hydrogen-dominated atmospheres and orbiting late-type stars. The modeled
planets have equilibrium temperatures ranging between 300 and 2000 K. For each
considered stellar mass, we account for three different values of the
high-energy stellar flux (i.e., low, moderate, and high activity). For each
computed model, we derive the atmospheric temperature, number density, bulk
velocity, X-ray and EUV (XUV) volume heating rates, and abundance of the
considered species as a function of distance from the planetary center. From
these quantities, we estimate the positions of the maximum dissociation and
ionisation, the mass-loss rate, and the effective radius of the XUV absorption.
We show that our results are in good agreement with previously published
studies employing similar codes. We further present an interpolation routine
capable to extract the modelling output parameters for any planet lying within
the grid boundaries. We use the grid to identify the connection between the
system parameters and the resulting atmospheric properties. We finally apply
the grid and the interpolation routine to estimate atmospheric evolutionary
tracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c... | astro-ph_EP |
Teegarden's Star revisited: A nearby planetary system with at least
three planets: The two known planets in the planetary system of Teegarden's Star are among
the most Earth-like exoplanets currently known. Revisiting this nearby
planetary system with two planets in the habitable zone aims at a more complete
census of planets around very low-mass stars. A significant number of new
radial velocity measurements from CARMENES, ESPRESSO, MAROON-X, and HPF, as
well as photometry from TESS motivated a deeper search for additional planets.
We confirm and refine the orbital parameters of the two know planets
Teegarden's Star b and c. We also report the detection of a third planet d with
an orbital period of 26.13+-0.04 d and a minimum mass of 0.82+-0.17 M_Earth. A
signal at 96 d is attributed to the stellar rotation period. The interpretation
of a signal at 172 d remains open. The TESS data exclude transiting
short-period planets down to about half an Earth radius. We compare the
planetary system architecture of very low-mass stars. In the currently known
configuration, the planetary system of Teegarden's star is dynamically quite
different from that of TRAPPIST-1, which is more compact, but dynamically
similar to others such as GJ 1002. | astro-ph_EP |
Effects of Dust Evolution on the Vertical Shear Instability in the Outer
Regions of Protoplanetary Disks: The vertical shear instability (VSI) is a hydrodynamical instability that
requires rapid gas cooling and has been suggested to operate in outer regions
of protoplanetary disks. The VSI drives turbulence with strong vertical
motions, which could regulate the dust growth and settling. However, dust
growth and settling can regulate the VSI because dust depletion makes gas
cooling inefficient in outer disk regions that are optically thin to their own
thermal emission. In this study, we quantify this potentially stabilizing
effects of dust evolution on the VSI based on the linear analysis. We construct
a model for calculating the cooling timescale, taking into account dust growth
beyond micron sizes and size-dependent settling. Combining the model with the
linear stability analysis, we map the region where the VSI operates, which we
call the VSI zone, and estimate the maximum growth rate at each radial
position. We find that dust growth as well as settling makes the VSI zone more
confined around the midplane. This causes a decrease in the growth rate because
the vertical shear of the rotation velocity, which is the source of the
instability, is weaker at lower altitude. In our default disk model with 0.01
solar masses, dust growth from 10 micron to 1 mm causes a decrease in the
growth rate by a factor of more than 10. The suppression of VSI-driven
turbulence by dust evolution may promote further dust evolution in the outer
regions and also explain a high degree of dust settling observed in the disk
around HL Tau. | astro-ph_EP |
High contrast imaging at 10 microns, a search for exoplanets around: Eps
Indi A, Eps Eri, Tau Ceti, Sirius A and Sirius B: The direct imaging of rocky exoplanets is one of the major science goals for
upcoming large telescopes. The contrast requirement for imaging such planets is
challenging. However, the mid-IR (InfraRed) regime provides the optimum
contrast to directly detect the thermal signatures of exoplanets in our solar
neighbourhood. We aim to exploit novel fast chopping techniques newly developed
for astronomy with the aid of adaptive optics to look for thermal signatures of
exoplanets around bright stars in the solar neighbourhood. We use the upgraded
VISIR (Very Large Telescope Imager and Spectrometer for the mid-InfraRed)
instrument with high contrast imaging (HCI) capability optimized for
observations at 10~$\mu$m to look for exoplanets around five nearby ($d$ < 4
pc) stars. The instrument provides an improved signal-to-noise (S/N) by a
factor of $\sim$4 in the N-band compared to standard VISIR for a given S/N and
time. In this work we achieve a detection sensitivity of sub-mJy, which is
sufficient to detect few Jupiter mass planets in nearby systems. Although no
detections are made we achieve most sensitive limits within $<2''$ for all the
observed targets compared to previous campaigns. For $\epsilon$ Indi A and
$\epsilon$ Eri we achieve detection limits very close to the giant planets
discovered by RV, with the limits on $\epsilon$ Indi A being the most sensitive
to date. Our non-detection therefore supports an older age for $\epsilon$ Indi
A. The results presented here show the promise for high contrast imaging and
exoplanet detections in the mid-IR regime. | astro-ph_EP |
Tidal dissipation in a homogeneous spherical body. I. Methods: A formula for the tidal dissipation rate in a spherical body is derived from
first principles, to correct some mathematical inaccuracies found in the
literature. The development is combined with the Darwin-Kaula formalism for
tides. Our intermediate results are compared with those by Zschau (1978) and
Platzman (1984). When restricted to the special case of an incompressible
spherical planet spinning synchronously without libration, our final formula
can be compared with the commonly used expression from Peale & Cassen (1978,
Eqn. 31). The two turn out to differ. In our expression, the contributions from
all Fourier modes are positive-definite, this not being the case of the formula
from Ibid. (The presence of negative terms in their formula was noticed by
Makarov 2013.) Examples of application of our expression for the tidal damping
rate are provided in the work by Makarov and Efroimsky (2014). | astro-ph_EP |
Insights on the dynamical history of the Fomalhaut system -
Investigating the Fom c hypothesis: The eccentric shape of the debris disk observed around Fomalhaut was first
attributed to Fom b, a companion detected near the belt inner-edge, but new
constraints on its orbit revealed that it is belt-crossing, highly eccentric
$(e \sim 0.6-0.9)$, and can hardly account for the shape of the belt. The best
scenario to explain this paradox is that there is another massive body in this
system, Fom c, which drives the debris disk shape. The resulting planetary
system is highly unstable, which hints at a dynamical scenario involving a
recent scattering of Fom b on its current orbit, potentially with the putative
Fom c.
Our goal is to give insights on the probability for Fom b to have been set on
its highly eccentric orbit by a close-encounter with the putative Fom c. We aim
to study in particular the part played by mean-motion resonances with Fom c,
which could have brought Fom b sufficiently close to Fom c for it to be
scattered on its current orbit, but also delay this scattering event.
Using N-body simulations, we found that the generation of orbits similar to
that of Fom b, either in term of dimensions or orientation, is a robust process
involving a scattering event and a further secular evolution of inner material
with an eccentric massive body such as the putative Fom c. We found in
particular that mean-motion resonances can delay scattering events, and thus
the production of Fom b-like orbits, on timescales comparable to the age of the
system, thus explaining the witnessing of an unstable configuration.
We conclude that Fom b probably originated from an inner resonance with Fom
c, which is at least Neptune-Saturn size, and was set on its current orbit by a
scattering event with Fom c. Since Fom b could not have formed from material in
resonance, our scenario also hints at former migration processes in this
planetary system. | astro-ph_EP |
A multiplicity study of transiting exoplanet host stars. I.
High-contrast imaging with VLT/SPHERE: We study the multiplicity of host stars to known transiting extra-solar
planets to test competing theories on the formation mechanisms of hot Jupiters.
We observed 45 exoplanet host stars using VLT/SPHERE/IRDIS to search for
potential companions. For each identified candidate companion we determined the
probability that it is gravitationally bound to its host by performing common
proper motion checks and modelling of synthetic stellar populations around the
host. We detected new candidate companions around K2-38, WASP-72, WASP-80,
WASP-87, WASP-88, WASP-108, WASP-118, WASP-120, WASP-122, WASP123, WASP-130,
WASP-131 and WASP-137. The closest candidates were detected at separations of
$0.124''\pm0.007''$ and $0.189''\pm0.003''$ around WASP-108 and WASP-131; the
measured $K$ band contrasts indicate that these are stellar companions of
$0.35\pm0.02\,M_{\odot}$ and $0.62^{+0.05}_{-0.04}\,M_{\odot}$, respectively.
Including the re-detection and confirmation of previously known companions in
13 other systems we derived a multiplicity fraction of
$55.4^{+5.9}_{-9.4}\,\%$. For the representative sub-sample of 40 hot Jupiter
host stars among our targets, the derived multiplicity rate is
$54.8^{+6.3}_{-9.9}\,\%$. Our data do not confirm any trend that systems with
eccentric planetary companions are preferably part of multiple systems. On
average, we reached a magnitude contrast of $8.5\pm0.9$ mag at an angular
separation of 0.5''. This allows to exclude additional stellar companions with
masses larger than $0.08$ M$_\odot$ for almost all observed systems; around the
closest and youngest systems this sensitivity is achieved at physical
separations as small as 10 au. The presented study shows that SPHERE is an
ideal instrument to detect and characterize close companions to exoplanetary
host stars. | astro-ph_EP |
Dynamics of Planetary Systems Within Star Clusters: Aspects of the Solar
System's Early Evolution: Most planetary systems -- including our own -- are born within stellar
clusters, where interactions with neighboring stars can help shape the system
architecture. This paper develops an orbit-averaged formalism to characterize
the cluster's mean-field effects as well as the physics of long-period stellar
encounters. Our secular approach allows for an analytic description of the
dynamical consequences of the cluster environment on its constituent planetary
systems. We analyze special cases of the resulting Hamiltonian, corresponding
to eccentricity evolution driven by planar encounters, as well as hyperbolic
perturbations upon dissipative disks. We subsequently apply our results to the
early evolution of our solar system, where the cluster's collective potential
perturbs the solar system's plane, and stellar encounters act to increase the
velocity dispersion of the Kuiper belt. Our results are two-fold: first, we
find that cluster effects can alter the mean plane of the solar system by
$\lesssim1\deg$, and are thus insufficient to explain the $\psi\approx6\deg$
obliquity of the sun. Second, we delineate the extent to which stellar flybys
excite the orbital dispersion of the cold classical Kuiper belt, and show that
while stellar flybys may grow the cold belt's inclination by the observed
amount, the resulting distribution is incompatible with the data.
Correspondingly, our calculations place an upper limit on the product of the
stellar number density and residence time of the sun in its birth cluster,
$\eta\,\tau\lesssim2\times10^4\,$Myr/pc$^3$. | astro-ph_EP |
ExoData: A python package to handle large exoplanet catalogue data: Exoplanet science often involves using the system parameters of real
exoplanets for tasks such as simulations, fitting routines, and target
selection for proposals. Several exoplanet catalogues are already well
established but often lack a version history and code friendly interfaces.
Software that bridges the barrier between the catalogues and code enables users
to improve the specific repeatability of results by facilitating the retrieval
of exact system parameters used in an articles results along with unifying the
equations and software used. As exoplanet science moves towards large data,
gone are the days where researchers can recall the current population from
memory. An interface able to query the population now becomes invaluable for
target selection and population analysis. ExoData is a Python interface and
exploratory analysis tool for the Open Exoplanet Catalogue. It allows the
loading of exoplanet systems into Python as objects (Planet, Star, Binary etc)
from which common orbital and system equations can be calculated and measured
parameters retrieved. This allows researchers to use tested code of the common
equations they require (with units) and provides a large science input
catalogue of planets for easy plotting and use in research. Advanced querying
of targets are possible using the database and Python programming language.
ExoData is also able to parse spectral types and fill in missing parameters
according to programmable specifications and equations. Examples of use cases
are integration of equations into data reduction pipelines, selecting planets
for observing proposals and as an input catalogue to large scale simulation and
analysis of planets. | astro-ph_EP |
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