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Forward Modeling of Solar Coronal Magnetic Field Measurements Based on a
Magnetic-field-induced Transition in Fe X: It was recently proposed that the intensity ratios of several extreme
ultraviolet spectral lines from the Fe X ion can be used to measure the solar
coronal magnetic field based on the magnetic-field-inducedtransition (MIT)
theory. To verify the suitability of this method, we performed forward
modelingwith a three-dimensional radiation magnetohydrodynamic model of a solar
active region. Intensities of several spectral lines from Fe X were synthesized
from the model. Based on the MIT theory, intensity ratios of the MIT line Fe X
257 A to several other Fe X lines were used to derive the magnetic field
strengths, which were then compared with the field strengths in the model. We
also developed a new method to simultaneously estimate the coronal density and
temperature from the Fe X 174/175 and 184/345 A line ratios. Using these
estimates, we demonstrated that the MIT technique can provide reasonably
accurate measurements of the coronal magnetic field in both on-disk and
off-limb solar observations. Our investigation suggests that a spectrometer
that can simultaneously observe the Fe X 174, 175, 184, 257, and 345 A lines
and allow an accurate radiometric calibration for these lines is highly desired
to achieve reliable measurements of the coronal magnetic field. We have also
evaluatedthe impact of the uncertainty in the Fe X 3p4 3d 4D5/2 and 4D7/2
energy difference on the magnetic field measurements. | astro-ph |
Microlensing by gas filaments: Gas in the interstellar matter is generally organized in filamentary
structures, which may be also relevant for a complementary explanation of the
dark matter in the Galactic halo. We examine the possibility that such
structures may act as gravitational microlenses on background sources. To this
purpose, we derive the general properties of a cylindrical lens and compare the
light curves produced by such microlensing events with those generated by
spherically symmetric clouds. We find that the establishment of the symmetry of
the lens through the sole analysis of the light curve may be problematic, while
the analysis of the astrometric shift of the centroid of the image can
discriminate between the two classes of clouds. On the basis of our analysis,
we find that only gas filaments with a very high density could be detectable.
Such clouds are unlikely to exist in a long-lived state. Therefore,
microlensing cannot discriminate on the existence and the relevance of gas
filaments in the Halo, which could well be present and escape detection by
ordinary microlensing surveys. | astro-ph |
Shock formation around planets orbiting M-dwarf stars: Bow shocks can be formed around planets due to their interaction with the
coronal medium of the host stars. The net velocity of the particles impacting
on the planet determines the orientation of the shock. At the Earth's orbit,
the (mainly radial) solar wind is primarily responsible for the formation of a
shock facing towards the Sun. However, for close-in planets that possess high
Keplerian velocities and are frequently located at regions where the host
star's wind is still accelerating, a shock may develop ahead of the planet. If
the compressed material is able to absorb stellar radiation, then the signature
of bow shocks may be observed during transits. Bow-shock models have been
investigated in a series of papers (Vidotto et al. 2010, 2011,a,b; Llama et al.
2011) for known transiting systems. Once the signature of a bow-shock is
observed, one can infer the magnetic field intensity of the transiting planet.
Here, we investigate the potential to use this model to detect magnetic fields
of (hypothetical) planets orbiting inside the habitable zone of M-dwarf stars.
For these cases, we show, by means of radiative transfer simulations, that the
detection of bow-shocks of planets surrounding M-dwarf stars may be more
difficult than for the case of close-in giant planets orbiting solar-type
stars. | astro-ph |
Performance and energy footprint assessment of FPGAs and GPUs on HPC
systems using Astrophysics application: New challenges in Astronomy and Astrophysics (AA) are urging the need for a
large number of exceptionally computationally intensive simulations. "Exascale"
(and beyond) computational facilities are mandatory to address the size of
theoretical problems and data coming from the new generation of observational
facilities in AA. Currently, the High Performance Computing (HPC) sector is
undergoing a profound phase of innovation, in which the primary challenge to
the achievement of the "Exascale" is the power-consumption. The goal of this
work is to give some insights about performance and energy footprint of
contemporary architectures for a real astrophysical application in an HPC
context. We use a state-of-the-art N-body application that we re-engineered and
optimized to exploit the heterogeneous underlying hardware fully. We
quantitatively evaluate the impact of computation on energy consumption when
running on four different platforms. Two of them represent the current HPC
systems (Intel-based and equipped with NVIDIA GPUs), one is a micro-cluster
based on ARM-MPSoC, and one is a "prototype towards Exascale" equipped with
ARM-MPSoCs tightly coupled with FPGAs. We investigate the behavior of the
different devices where the high-end GPUs excel in terms of time-to-solution
while MPSoC-FPGA systems outperform GPUs in power consumption. Our experience
reveals that considering FPGAs for computationally intensive application seems
very promising, as their performance is improving to meet the requirements of
scientific applications. This work can be a reference for future platforms
development for astrophysics applications where computationally intensive
calculations are required. | astro-ph |
Investigating the damping rate of phase-mixed Alfven waves: Context: This paper investigates the effectiveness of phase mixing as a
coronal heating mechanism. A key quantity is the wave damping rate, $\gamma$,
defined as the ratio of the heating rate to the wave energy.
Aims: We investigate whether or not laminar phase-mixed Alfv\'en waves can
have a large enough value of $\gamma$ to heat the corona. We also investigate
the degree to which the $\gamma$ of standing Alfv\'en waves which have reached
steady-state can be approximated with a relatively simple equation. Further
foci of this study are the cause of the reduction of $\gamma$ in response to
leakage of waves out of a loop, the quantity of this reduction, and how
increasing the number of excited harmonics affects $\gamma$.
Results: We find that at observed frequencies $\gamma$ is too small to heat
the corona by approximately three orders of magnitude. Therefore, we believe
that laminar phase mixing is not a viable stand-alone heating mechanism for
coronal loops. We show that $\gamma$ is largest at resonance. We find our
simple equation provides a good estimate for the damping rate (within
approximately 10% accuracy) for resonant field lines. However, away from
resonance, the equation provides a poor estimate, predicting $\gamma$ to be
orders of magnitude too large. We find that leakage acts to reduce $\gamma$ but
plays a negligible role if $\gamma$ is of the order required to heat the
corona. If the wave energy follows a power spectrum with slope -5/3 then
$\gamma$ grows logarithmically with the number of excited harmonics. If the
number of excited harmonics is increased by much more than 100, then the
heating is mainly caused by gradients that are parallel to the field rather
than perpendicular to it. Therefore, in this case, the system is not heated
mainly by phase mixing. | astro-ph |
K2 Ultracool Dwarfs Survey. V. High superflare rates on rapidly rotating
late-M dwarfs: We observed strong superflares (defined as flares with energy in excess of
10^33 erg) on three late-M dwarfs: 2MASS J08315742+2042213 (hereafter
2M0831+2042; M7 V), 2MASS J08371832+2050349 (hereafter 2M0837+2050; M8 V) and
2MASS J08312608+2244586 (hereafter 2M0831+2244; M9 V). 2M0831+2042 and
2M0837+2050 are members of the young (~700 Myr) open cluster Praesepe. The
strong superflare on 2M0831+2042 has an equivalent duration (ED) of 13.7 hr and
an estimated energy of 1.3 X 10^35 erg. We observed five superflares on
2M0837+2050, on which the strongest superflare has an ED of 46.4 hr and an
estimated energy of 3.5 X 10^35 erg. This energy is larger by 2.7 orders of
magnitude than the largest flare observed on the older (7.6 Gyr) planet-hosting
M8 dwarf TRAPPIST-1. Furthermore, we also observed five superflares on
2M0831+2244 which is probably a field star. The estimated energy of the
strongest superflare on 2M0831+2244 is 6.1 X 10^34 erg. 2M0831+2042,
2M0837+2050 and 2MASS J0831+2244 have rotation periods of 0.556\pm0.002,
0.193\pm0.000 and 0.292\pm0.001 d respectively, which are measured by using K2
light curves. We compare the flares of younger targets with those of TRAPPIST-1
and discuss the possible impacts of such flares on planets in the habitable
zone of late-M dwarfs. | astro-ph |
The Decrease of Specific Angular Momentum and the Hot Toroid Formation:
The Massive Clump G10.6-0.4: This is the first paper of our series of high resolution (1") studies of the
massive star forming region G10.6--0.4. We present the emission line
observations of the hot core type tracers (O$^{13}$CS, OCS, SO$_{2}$) with
$\sim$0$"$.5 resolution. By comparing the results to the high--resolution
NH$_{3}$ absorption line observation, we confirm for the first time the
rotationally flattened hot toroid in the central $<$0.1 pc region, which has a
rotational axis perpendicular to its geometrical major axis.
In addition, we present the observations of NH$_{3}$, $^{13}$CS, and
CH$_{3}$CN with $\sim$1$"$ resolution, and follow the dynamics of the molecular
accretion flow from the 0.3 pc radius to the inner 0.03 pc radius. With
reference to the rotational axis of the hot toroid, we measure the rotational
velocity from the molecular emission in the region. The results are consistent
with an envelope with a rapid decrease of the specific angular momentum from
the outer to the inner region. These new results improve the current
understanding of the molecular accretion flow in an ultracompact (UC)
H\textsc{ii} region created by the embedded O-type cluster. | astro-ph |
2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the
CHIMERA Code: Much progress in realistic modeling of core-collapse supernovae has occurred
recently through the availability of multi-teraflop machines and the increasing
sophistication of supernova codes. These improvements are enabling simulations
with enough realism that the explosion mechanism, long a mystery, may soon be
delineated. We briefly describe the CHIMERA code, a supernova code we have
developed to simulate core-collapse supernovae in 1, 2, and 3 spatial
dimensions. We then describe the results of an ongoing suite of 2D simulations
initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all
exhibited explosions and are currently in the expanding phase with the shock at
between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in
3 spatial dimensions initiated from the 15 solar mass progenitor. | astro-ph |
Large-Scale Structure and Future Surveys: As the 2dF Galaxy Redshift Survey and Sloan Digital Sky Survey move toward
completion, it is time to ask what the next generation of survey of large-scale
structure should be. I discuss some of the cosmological justifications for such
surveys and conclude that surveys at z=3 offer a critical advantage in their
ability to access linear-regime clustering at scales smaller than any current
survey and even the CMB. I discuss a possible implementation of such a survey
and highlight some of the potential science return. | astro-ph |
The X-ray Flux Distribution of Sagittarius A* as Seen by Chandra: We present a statistical analysis of the X-ray flux distribution of Sgr A*
from the Chandra X-ray Observatory's 3 Ms Sgr A* X-ray Visionary Project (XVP)
in 2012. Our analysis indicates that the observed X-ray flux distribution can
be decomposed into a steady quiescent component, represented by a Poisson
process with rate $Q=(5.24\pm0.08)\times10^{-3}$ cts s$^{-1},$ and a variable
component, represented by a power law process ($dN/dF\propto F^{-\xi},$
$\xi=1.92_{-0.02}^{+0.03}$). This slope matches our recently-reported
distribution of flare luminosities. The variability may also be described by a
log-normal process with a median unabsorbed 2-8 keV flux of
$1.8^{+0.9}_{-0.6}\times10^{-14}$ erg s$^{-1}$ cm$^{-2}$ and a shape parameter
$\sigma=2.4\pm0.2,$ but the power law provides a superior description of the
data. In this decomposition of the flux distribution, all of the intrinsic
X-ray variability of Sgr A* (spanning at least three orders of magnitude in
flux) can be attributed to flaring activity, likely in the inner accretion
flow. We confirm that at the faint end, the variable component contributes ~10%
of the apparent quiescent flux, as previously indicated by our statistical
analysis of X-ray flares in these Chandra observations. Our flux distribution
provides a new and important observational constraint on theoretical models of
Sgr A*, and we use simple radiation models to explore the extent to which a
statistical comparison of the X-ray and infrared can provide insights into the
physics of the X-ray emission mechanism. | astro-ph |
Systematic bias in the estimate of cluster mass and the fluctuation
amplitude from cluster abundance statistics: We revisit the estimate of the mass fluctuation amplitude, sigma_8, from the
observational X-ray cluster abundance. In particular, we examine the effect of
the systematic difference between the cluster virial mass estimated from the
X-ray spectroscopy, M_{vir, spec}, and the true virial mass of the
corresponding halo, M_{vir}. Mazzotta et al. (2004) recently pointed out the
possibility that alpha_M = M_{vir, spec}/M_{vir} is systematically lower than
unity. We perform the statistical analysis combining the latest X-ray cluster
sample and the improved theoretical models and find that sigma_8 \sim 0.76 +/-
0.01 + 0.50 (1-alpha_M) for 0.5 \le alpha_M \le 1, where the quoted errors are
statistical only. Thus if alpha_M \sim 0.7, the value of sigma_8 from cluster
abundance alone is now in better agreement with other cosmological data
including the cosmic microwave background, the galaxy power spectrum and the
weak lensing data. The current study also illustrates the importance of
possible systematic effects in mapping real clusters to underlying dark halos
which changes the interpretation of cluster abundance statistics. | astro-ph |
Tracing the Physical Conditions in Active Galactic Nuclei with
Time-Dependent Chemistry: We present an extension of the code ProDiMo that allows for a modeling of
processes pertinent to active galactic nuclei and to an ambient chemistry that
is time dependent. We present a proof-of-concept and focus on a few
astrophysically relevant species, e.g., H+, H2+ and H3+; C+ and N+; C and O; CO
and H2O; OH+, H2O+ and H3O+; HCN and HCO+. We find that the freeze-out of water
is strongly suppressed and that this affects the bulk of the oxygen and carbon
chemistry occurring in AGN. The commonly used AGN tracer HCN/HCO+ is strongly
time-dependent, with ratios that vary over orders of magnitude for times longer
than 10^4 years. Through ALMA observations this ratio can be used to probe how
the narrow-line region evolves under large fluctuations in the SMBH accretion
rate. Strong evolutionary trends, on time scales of 10^4-10^8 years, are also
found in species such as H3O+, CO, and H2O. These reflect, respectively, time
dependent effects in the ionization balance, the transient nature of the
production of molecular gas, and the freeze-out/sublimation of water. | astro-ph |
Cosmological model: from initial conditions to structure formation: Observational cosmology is on the verge of new discoveries that will change
the essence of our world-view. The matter concerns origin of initial conditions
and physics of dark matter. | astro-ph |
Multiple Populations and a CH Star Found in the 300S Globular Cluster
Stellar Stream: Milky Way globular clusters (GCs) display chemical enrichment in a phenomenon
called multiple stellar populations (MSPs). While the enrichment mechanism is
not fully understood, there is a correlation between a cluster's mass and the
fraction of enriched stars found therein. However, present-day GC masses are
often smaller than their masses at the time of formation due to dynamical mass
loss. In this work, we explore the relationship between mass and MSPs using the
stellar stream 300S. We present the chemical abundances of eight red giant
branch member stars in 300S with high-resolution spectroscopy from
Magellan/MIKE. We identify one enriched star characteristic of MSPs and no
detectable metallicity dispersion, confirming that the progenitor of 300S was a
globular cluster. The fraction of enriched stars (12.5\%) observed in our 300S
stars is less than the 50\% of stars found enriched in Milky Way GCs of
comparable present-day mass ($\sim10^{4.5}$\msun). We calculate the mass of
300S's progenitor and compare it to the initial masses of intact GCs, finding
that 300S aligns well with the trend between the system mass at formation and
enrichment. 300S's progenitor may straddle the critical mass threshold for the
formation of MSPs and can therefore serve as a benchmark for the stellar
enrichment process. Additionally, we identify a CH star, with high abundances
of \textit{s}-process elements, probably accreted from a binary companion. The
rarity of such binaries in intact GCs may imply stellar streams permit the
survival of binaries that would otherwise be disrupted. | astro-ph |
No self-shadowing instability in 2D radiation-hydrodynamical models of
irradiated protoplanetary disks: Theoretical models of protoplanetary disks including stellar irradiation
often show a spontaneous amplification of scale height perturbations, produced
by the enhanced absorption of starlight in enlarged regions. In turn, such
regions cast shadows on adjacent zones that consequently cool down and shrink,
eventually leading to an alternating pattern of overheated and shadowed
regions. Previous investigations have proposed this to be a real self-sustained
process, the so-called self-shadowing or thermal wave instability, which could
naturally form frequently observed disk structures such as rings and gaps, and
even potentially enhance the formation of planetesimals. All of these, however,
have assumed in one way or another vertical hydrostatic equilibrium and
instantaneous radiative diffusion throughout the disk. In this work we present
the first study of the stability of accretion disks to self-shadowing that
relaxes these assumptions, relying instead on radiation-hydrodynamical
simulations. We first construct hydrostatic disk configurations by means of an
iterative procedure and show that the formation of a pattern of enlarged and
shadowed regions is a direct consequence of assuming instantaneous radiative
diffusion. We then let these solutions evolve in time, which leads to a fast
damping of the initial shadowing features in layers close to the disk surface.
These thermally relaxed layers grow towards the midplane until all temperature
extrema in the radial direction are erased in the entire disk. Our results
suggest that radiative cooling and gas advection at the disk surface prevent a
self-shadowing instability from forming, by damping temperature perturbations
before these reach lower, optically thick regions. | astro-ph |
The Structure of HE 1104-1805 from Infrared to X-Ray: The gravitationally lensed quasar HE 1104-1805 has been observed at a variety
of wavelengths ranging from the mid-infrared to X-ray for nearly 20 years. We
combine flux ratios from the literature, including recent Chandra data, with
new observations from the SMARTS telescope and HST, and use them to investigate
the spatial structure of the central regions using a Bayesian Monte Carlo
analysis of the microlensing variability. The wide wavelength coverage allows
us to constrain not only the accretion disk half-light radius r_1/2, but the
power-law slope \xi\ of the size-wavelength relation r_1/2 ~ \lambda^\xi. With
a logarithmic prior on the source size, the (observed-frame) R-band half-light
radius log(r_1/2/cm) is 16.0+0.3-0.4, and the slope \xi\ is 1.0+0.30-0.56. We
put upper limits on the source size in soft (0.4-1.2 keV) and hard (1.2-8 keV)
X-ray bands, finding 95% upper limits on log (r_1/2/cm) of 15.33 in both bands.
A linear prior yields somewhat larger sizes, particularly in the X-ray bands.
For comparison, the gravitational radius, using a black hole mass estimated
using the H\beta\ line, is log(r_g/cm) = 13.94. We find that the accretion disk
is probably close to face-on, with cos i = 1.0 being four times more likely
than cos i = 0.5. We also find probability distributions for the mean mass of
the stars in the foreground lensing galaxy, the direction of the transverse
peculiar velocity of the lens, and the position angle of the projected
accretion disk's major axis (if not face-on). | astro-ph |
The Quark-Hadron Phase Transition, QCD Lattice Calculations and
Inhomogeneous Big-Bang Nucleosynthesis: We review recent lattice QCD results for the surface tension at the finite
temperature quark-hadron phase transition and discuss their implications on the
possible scale of inhomogeneities. In the quenched approximation the average
distance between nucleating centers is smaller than the diffusion length of a
protron, so that inhomogeneities are washed out by the time nucleosynthesis
sets in. Consequently the baryon density fluctuations formed by a QCD phase
transition in the early universe cannot significantly affect standard big-bang
nucleosynthesis calculations and certainly cannot allow baryons to close the
universe. At present lattice results are inconclusive when dynamical fermions
are included. | astro-ph |
Modeling the flyby anomalies with dark matter scattering: update with
additional data and further predictions: We continue our exploration of whether the flyby anomalies can be explained
by scattering of spacecraft nucleons from dark matter gravitationally bound to
the earth, with the addition of data from five new flybys to that from the
original six. We continue to use our model in which inelastic and elastic
scatterers populate shells generated by the precession of circular orbits with
normals tilted with respect to the earth's axis. With 11 data points and 8
parameters in the model, a statistically meaningful fit is obtained with a
chi-squared of 2.7. We give plots of the anomalous acceleration along the
spacecraft trajectory, and the cumulative velocity change, for the five flybys
which exhibit a significant nonzero anomaly. We also discuss implications of
the fit for dark matter-nucleon cross sections, give the prediction of our fit
for the anomaly to be expected from the future Juno flyby, and give predictions
of our fit for flyby orbit orientation changes. In addition we give formulas
for estimating the flyby temperature increase caused by dark matter inelastic
scattering, and for the fraction of flyby nucleons undergoing such scatters.
Finally, for circular satellite orbits, we give a table of predicted secular
changes in orbit radius. These are much too large to be reasonable -- comparing
with data for COBE and GP-B supplied to us by Edward Wright (after the first
version of this paper was posted), we find that our model predicts changes in
orbit radius that are too large by many orders of magnitude. So the model
studied here is ruled out. We conclude that further modeling of the flyby
anomalies must simultaneously attempt to fit constraints coming from satellite
orbits. | astro-ph |
Ionizing photon production of Population III stars: effects of rotation,
convection, and initial mass function: The first stars are thought to be one of the dominant sources of hydrogen
reionization in the early Universe, with their high luminosities and surface
temperatures expected to drive high ionizing photon production rates. In this
work, we take our Geneva stellar evolution models of zero-metallicity stars and
predict their production rates of photons capable to ionize H, He I and He II,
based on a blackbody approximation. We present analytical fits in the range
1.7-500 solar masses. We then explore the impact of stellar initial mass,
rotation, and convective overshooting for individual stars. We have found that
ionizing photon production rates increase with increasing initial mass. For the
rotational velocities considered we see changes of up to 25% to ionizing
photons produced. This varies with initial mass and ionizing photon species and
reflects changes to surface properties due to rotation. We have also found that
higher convective overshooting increases ionizing photon production by
approximately 20% for the change in overshooting considered here. For stellar
populations, we explore how the production of ionizing photons varies as a
function of the initial mass function (IMF) slope, and minimum and maximum
initial masses. For a fixed population mass we have found changes of the order
of 20-30% through varying the nature of the IMF. This work presents ionizing
photon production predictions for the most up to date Geneva stellar evolution
models of Population III stars, and provides insight into how key evolutionary
parameters impact the contribution of the first stars to reionization. | astro-ph |
Reverberation measurement of the inner radius of the dust torus in NGC
4151 during 2008-2013: We investigate the correlation between infrared (JHKL) and optical (B) fluxes
of the variable nucleus of the Seyfert galaxy NGC 4151 using partially
published data for the last 6 years (2008-2013.). Here we are using the same
data as in Oknyansky et al. (2014), but include also optical (B) data from Guo
et al. We find that the lag of flux in all the infrared bands is the same, 40
+- 6 days, to within the measurement accuracy. Variability in the J and K bands
is not quite simultaneous, perhaps due to the differing contributions of the
accretion disk in these bands. The lag found for the K band compared with the B
band is not significantly different from earlier values obtained for the period
2000-2007. However, finding approximately the same lags in all IR bands for
2008-2013 differs from previous results at earlier epochs when the lag
increased with increasing wavelength. Examples of almost the same lag in
different IR bands are known for some other active nuclei. In the case of NGC
4151 it appears that the relative lags between the IR bands may be different in
different years. The available data, unfortunately, do not allow us to
investigate a possible change in the lags during the test interval. We discuss
our results in the framework of the standard model where the variable infrared
radiation is mainly due to thermal re-emission from the part of the dusty torus
closest to the central source. There is also a contribution of some IR emission
from the accretion disk, and this contribution increases with decreasing
wavelength. Some cosmological applications of obtained results are discussed. | astro-ph |
Global 21-cm signal extraction from foreground and instrumental effects
I: Pattern recognition framework for separation using training sets: The sky-averaged (global) highly redshifted 21-cm spectrum from neutral
hydrogen is expected to appear in the VHF range of $\sim20-200$ MHz and its
spectral shape and strength are determined by the heating properties of the
first stars and black holes, by the nature and duration of reionization, and by
the presence or absence of exotic physics. Measurements of the global signal
would therefore provide us with a wealth of astrophysical and cosmological
knowledge. However, the signal has not yet been detected because it must be
seen through strong foregrounds weighted by a large beam, instrumental
calibration errors, and ionospheric, ground and radio-frequency-interference
effects, which we collectively refer to as "systematics". Here, we present a
signal extraction method for global signal experiments which uses Singular
Value Decomposition (SVD) of "training sets" to produce systematics basis
functions specifically suited to each observation. Instead of requiring precise
absolute knowledge of the systematics, our method effectively requires precise
knowledge of how the systematics can vary. After calculating eigenmodes for the
signal and systematics, we perform a weighted least square fit of the
corresponding coefficients and select the number of modes to include by
minimizing an information criterion. We compare the performance of the signal
extraction when minimizing various information criteria and find that
minimizing the Deviance Information Criterion (DIC) most consistently yields
unbiased fits. The methods used here are built into our widely applicable,
publicly available Python package, $\texttt{pylinex}$, which analytically
calculates constraints on signals and systematics from given data, errors, and
training sets. | astro-ph |
The iron and oxygen content of LMC Classical Cepheids and its
implications for the Extragalactic Distance Scale and Hubble constant: Classical Cepheids are primary distance indicators and a crucial stepping
stone to determining the present-day Hubble constant Ho to the precision and
accuracy required to constrain apparent deviations from the LCDM Concordance
Cosmological Model. We have measured the iron and oxygen abundances of of 89
Cepheids in the LMC, one of the anchors of the local Distance Scale,
quadrupling the prior sample and including 68 of the 70 Cepheids used to
constrain Ho by the SH0ES program. The goal is to constrain the extent to which
the Cepheid luminosity is influenced by their chemical composition, an
important contributor to the uncertainty on the determination of the Ho itself
and a critical factor in the internal consistency of the distance ladder. We
have derived stellar parameters and abundances from a self-consistent
spectroscopic analysis based on Equivalent Width of absorption lines. The
[Fe/H] distribution of LMC Cepheids is a single Gaussian with a mean of
-0.4079+-0.003 dex (0.1 dex systematic uncertainty) and sigma 0.076+-0.003 dex.
The latter is fully compatible with the measurement error and supports the low
dispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The
uniformity of the abundance has the important consequence that the LMC Cepheids
alone cannot provide any meaningful constraint on the dependence of the Cepheid
Period-Luminosity relation on chemical composition at any wavelength. This
revises a prior claim based on a small sample of 22 LMC Cepheids that there was
little dependence (or uncertainty) between composition and NIR luminosity, a
conclusion which would produce a conflict between anchors of the distance
ladder with different mean abundance. The chemical homogeneity of the LMC
Cepheid population makes it an ideal environment to calibrate the metallicity
dependence between the more metal poor SMC and metal rich Milky Way and
NGC4258. | astro-ph |
Dwarf pulses of 10 pulsars detected by FAST: How pulsars radiate is a long-standing problem. Detailed polarization
measurements of individual pulses shed light on currently unknown emission
processes. Recently, based on supersensitive observations, dwarf pulses have
been recognized as weak narrow pulses often appearing during the nulling state.
In this study, we report the detection of dwarf pulses from ten pulsars, PSRs
B0525+21, B1237+25, J1538+2345, J1824$-$0127, J1851$-$0053, B1901+10, J1939+10,
B1944+17, B2000+40 and J2112+4058, based on observations conducted with the
Five-hundred-meter Aperture Spherical radio Telescope. Dwarf pulses of five
pulsars are clearly discernible in the two-dimensional distribution of pulse
intensity and pulse width. For the other five pulsars, PSRs J1538+2345,
J1824$-$0127, J1939+10, B2000+40, and J2112+4058, only a few dwarf pulses are
detected from pulse stacks. The dwarf pulses can emerge in both cone and core
emission components for PSR B1237+25, and the polarization angles of these
dwarf pulses are mostly in the orthogonal polarization mode of normal pulses
for PSR B1944+17. In general, pulsars with detected dwarf pulses tend to be
located within the "death valley" region of the distribution of pulsar periods
and period derivatives. | astro-ph |
Sunward propagating whistler waves collocated with localized magnetic
field holes in the solar wind: Parker Solar Probe observations at 35.7 Sun
radii: Observations by the Parker Solar Probe mission of the solar wind at about
35.7 solar radii reveal the existence of whistler wave packets with frequencies
below 0.1 f/fce (20-80 Hz in the spacecraft frame). These waves often coincide
with local minima of the magnetic field magnitude or with sudden deflections of
the magnetic field that are called switchbacks. Their sunward propagation leads
to a significant Doppler frequency downshift from 200-300 Hz to 20-80 Hz (from
0.2 f/fce to 0.5 f/fce). The polarization of these waves varies from
quasi-parallel to significantly oblique with wave normal angles that are close
to the resonance cone. Their peak amplitude can be as large as 2 to 4 nT. Such
values represent approximately 10% of the background magnetic field, which is
considerably more than what is observed at 1 a.u. Recent numerical studies show
that such waves may potentially play a key role in breaking the heat flux and
scattering the Strahl population of suprathermal electrons into a halo
population. | astro-ph |
Probing the Galactic Bulge with deep Adaptive Optics imaging: the age of
NGC 6440: We present first results of a pilot project aimed at exploiting the
potentiality of ground based adaptive optics imaging in the near infrared to
determine the age of stellar clusters in the Galactic Bulge. We have used a
combination of high resolution adaptive optics (ESO-VLT NAOS-CONICA) and
wide-field (ESO-NTT-SOFI) photometry of the metal rich globular cluster NGC
6440 located towards the inner Bulge, to compute a deep color magnitude diagram
from the tip of the Red Giant Branch down to J~22$, two magnitudes below the
Main Sequence Turn Off (TO). The magnitude difference between the TO level and
the red Horizontal Branch has been used as an age indicator. It is the first
time that such a measurement for a bulge globular cluster has been obtained
with a ground based telescope. From a direct comparison with 47 Tuc and with a
set of theoretical isochrones, we concluded that NGC 6440 is old and likely
coeval to 47 Tuc. This result adds a new evidence that the Galactic Bulge is ~2
Gyr younger at most than the pristine, metal poor population of the Galactic
Halo. | astro-ph |
Dark Energy Probes in Light of the CMB: CMB observables have largely fixed the expansion history of the universe in
the deceleration regime and provided two self-calibrated absolute standards for
dark energy studies: the sound horizon at recombination as a standard ruler and
the amplitude of initial density fluctuations. We review these inferences and
expose the testable assumptions about recombination and reionization that
underly them. Fixing the deceleration regime with CMB observables, deviations
in the distance and growth observables appear most strongly at z=0 implying
that accurate calibration of local and CMB standards may be more important than
redshift range or depth. The single most important complement to the CMB for
measuring the dark energy equation of state at z~0.5 is a determination of the
Hubble constant to better than a few percent. Counterintuitively, with fixed
fractional distance errors and relative standards such as SNe, the Hubble
constant measurement is best achieved in the high redshift deceleration regime.
Degeneracies between the evolution and current value of the equation of state
or between its value and spatial curvature can be broken if percent level
measurement and calibration of distance standards can be made at intermediate
redshifts or the growth function at any redshift in the acceleration regime. We
compare several dark energy probes available to a wide and deep optical survey:
baryon features in galaxy angular power spectra and the growth rate from
galaxy-galaxy lensing, shear tomography and the cluster abundance. | astro-ph |
X-ray and radio studies of SNR CTB 37B hosting the magnetar CXOU
J171405.7-381031: We present a Chandra and XMM-Newton study of the SNR CTB 37B, along with
archival radio observations. In radio wavelengths, CTB 37B is an incomplete
shell showing bright emission from the eastern side while the X-ray morphology
shows diffuse emission from regions surrounding the magnetar CXOU
J171405.7-381031. We used archival HI absorption measurements to constrain the
distance to the remnant as 9.8+/-1.5 kpc. The X-ray spectrum of the remnant is
described by a thermal model in the 1-5 keV energy range, with a temperature of
1.3+/-0.1 keV. The abundances from the spectral fits are consistent with being
solar or sub-solar. A small region of diffuse emission is seen to the southern
side of the remnant, best fitted by a nonthermal spectrum with an unusually
hard photon index of 1.3+/-0.3. Assuming a distance of 9.8 kpc to the SNR, we
infer a shock velocity of 915+/-70 km/s and explosion energy of (1.8+/-0.6)e50
ergs. The overall imaging and spectral properties of CTB 37B favor the
interpretation of a young SNR (6200 yr) propagating in a low-density medium,
under the assumption of a Sedov evolutionary phase. | astro-ph |
Concentration, Ellipsoidal Collapse, and the Densest Dark Matter haloes: The smallest dark matter haloes are the first objects to form in the
hierarchical structure formation of cold dark matter (CDM) cosmology and are
expected to be the densest and most fundamental building blocks of CDM
structures in our universe. Nevertheless, the physical characteristics of these
haloes have stayed illusive, as they remain well beyond the current resolution
of N-body simulations (at redshift zero). However, they dominate the
predictions (and uncertainty) in expected dark matter annihilation signal,
amongst other astrophysical observables. Using the conservation of total energy
and the ellipsoidal collapse framework, we can analytically find the mean and
scatter of concentration $c$ and 1-D velocity dispersion $\sigma_{\rm 1d}$ for
haloes of different virial mass $M_{200}$. Both $c$ and $\sigma_{\rm
1d}/M_{200}^{1/3}$ are in good agreement with numerical results within the
regime probed by simulations -- slowly decreasing functions of mass that
approach constant values at large masses. In particular, the predictions for
the 1-D velocity dispersion of cluster mass haloes are surprisingly robust as
the inverse heat capacity of cosmological haloes crosses zero at $M_{200} \sim
10^{14} M_\odot$. However, we find that current extrapolations from simulations
to smallest CDM haloes dramatically depend on the assumed profile (e.g. NFW vs.
Einasto) and fitting function, which is why theoretical considerations, such as
the one presented here, can significantly constrain the range of feasible
predictions. | astro-ph |
Resurrecting Quartic and Quadratic inflaton potentials in two-field
inflationary model: After the release of the PLANCK data, it is evident that inflationary
paradigm has stood the test of time. Even though, it is difficult to realise
inflationary paradigm in a particle physics model as the present observations
have ruled out the simplest quartic and quadratic inflationary potentials,
which generically arise in particle physics. We would show that such simplest
inflationary potentials can evade discrepancies with observations, if the
inflaton field is assisted by another scalar during inflation. Moreover, unlike
other multifield models, our model yields no isocurvature perturbations and
negligible non-Gaussianity, making it more compatible with the present data.
Above all, our model can also be realised in the framework of SUGRA. | astro-ph |
A "metric" semi-Lagrangian Vlasov-Poisson solver: We propose a new semi-Lagrangian Vlasov-Poisson solver. It employs elements
of metric to follow locally the flow and its deformation, allowing one to find
quickly and accurately the initial phase-space position $Q(P)$ of any test
particle $P$, by expanding at second order the geometry of the motion in the
vicinity of the closest element. It is thus possible to reconstruct accurately
the phase-space distribution function at any time $t$ and position $P$ by
proper interpolation of initial conditions, following Liouville theorem. When
distorsion of the elements of metric becomes too large, it is necessary to
create new initial conditions along with isotropic elements and repeat the
procedure again until next resampling. To speed up the process, interpolation
of the phase-space distribution is performed at second order during the
transport phase, while third order splines are used at the moments of
remapping. We also show how to compute accurately the region of influence of
each element of metric with the proper percolation scheme. The algorithm is
tested here in the framework of one-dimensional gravitational dynamics but is
implemented in such a way that it can be extended easily to four or
six-dimensional phase-space. It can also be trivially generalised to plasmas. | astro-ph |
The sigma - L correlation in Nearby Early-Type Galaxies: Early-type galaxy velocity dispersions and luminosities are correlated. The
correlation estimated in local samples (< 100 Mpc) differs from that measured
more recently in the SDSS. This is true even when systematics in the SDSS
photometric and spectroscopic parameters have been accounted-for. We show that
this is also true for the ENEAR sample if galaxy luminosities are estimated
using distances which have been corrected for peculiar motions. We then show
that, because the estimate of the `true' distance is derived from a correlation
with velocity dispersion, in this case the D_n-sigma relation, using it in the
sigma-L relation leads to an artificially tight relation with a biased slope.
Making no correction for peculiar velocities results in a sigma-L relation
which is very similar to that of the SDSS, although with larger scatter. We
also measure the sigma-L correlation in a mock ENEAR catalog, in which the
underlying galaxy sample has the same sigma-L correlation as seen in the SDSS.
The mock catalog produces the same D_n-sigma relation as the data, the same
biased slope when D_n-sigma distances are used to estimate luminosities, and
good agreement with the input sigma-L relation when redshift is used as the
distance indicator. This provides further evidence that the true sigma-L
relation of ENEAR galaxies is indeed very similar to that of SDSS early-types.
Our results suggest that local sigma-L relations which are based on Fundamental
Plane distances should also be re-evaluated. Our findings also have important
implications for black hole demographics; the best direct estimates of the
masses of supermassive black holes come from local galaxies, so estimates of
the black hole mass function are more safely made by working with the Mbh-sigma
correlation than with Mbh-L. | astro-ph |
On the methanol masers in G9.62+0.20E and G188.95+0.89: A comparison between the observed light curves of periodic masers in
G9.62+0.20E and G188.95+0.89 and the results of a simple colliding-wind binary
model is made to establish whether the flaring and other time-dependent
behaviour of the masers in these two star forming regions can be ascribed to
changes in the environment of the masers or in the continuum emission from
parts of the background \ion{H}{2} region. It is found that the light curves of
widely different shape and amplitude in these two objects can be explained
within the framework of a periodic pulse of ionizing radiation that raises the
electron density in a volume of partially ionized gas against which the masers
are projected. It is also shown that the decay of the 11.405 $\kmps$ maser in
G188.95+0.89 can be explained very well in terms of the recombination of the
ionized gas against which the maser is projected while it would require very
special conditions to explain it in terms of changes in environment of the
maser. We conclude that for G9.62+0.20E and G188.95+0.89 the observed changes
in the masers are most likely due to changes in the background free-free
emission which is amplified by the masers. | astro-ph |
On the phase-space structure of the Milky Way dark-matter halo: We analyse a high resolution simulation of the formation of a cluster's
dark-matter halo in a $\Lambda$CDM cosmology (Springel et al. 2001). The
resolution achieved allows us to map the phase-space structure in detail, and
characterize its evolution and degree of lumpiness. Scaling down the cluster
halo to a Milky-Way size halo, we probe the substructure expected in the solar
neighbourhood. Here we specifically address the relevance of such substructure
for direct detection experiments aimed at determining the nature of
dark-matter. | astro-ph |
Viscosity driven instability in rotating relativistic stars: We investigate the viscosity driven instability in rotating relativistic
stars by means of an iterative approach. We focus on polytropic rotating
equilibrium stars and impose an m=2 perturbationin the lapse. We vary both the
stiffness of the equation of state and the compactness of the star to study
those effects on the value of the threshold. For a uniformly rotating star, the
criterion T/W, where T is the rotational kinetic energy and W is the
gravitational binding energy, mainly depends on the compactness of the star and
takes values around 0.13 ~ 0.16, which differ slightly from that of Newtonian
incompressible stars (~ 0.14). For differentially rotating stars, the critical
value of T/W is found to span the range 0.17 - 0.25. This is significantly
larger than the uniformly rotating case with the same compactness of the star.
Finally we discuss a possibility of detecting gravitational waves from
viscosity driven instability with ground-based interferometers. | astro-ph |
A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies
of the Binary X-ray Pulsar 4U0115+63 with RXTE: The present paper reports on the RXTE observations of the binary X-ray pulsar
4U0115+63, covering an outburst in 1999 March-April with 44 pointings. The 3-30
keV PCA spectra and the 15-50 keV HEXTE spectra were analyzed jointly for the
cyclotron resonance features. When the 3-50 keV luminosity at an assumed
distance of 7 kpc was in the range (5-13)x10^{37} erg s^{-1}, harmonic double
cyclotron features were observed in absorption at ~11 and ~22 keV, as was
measured previously during typical outbursts. As the luminosity decreased below
\~5x10^{37} erg s^{-1}, the second resonance disappeared, and the fundamental
resonance energy gradually increased, up to $\sim$16 keV at 0.16x10^{37} erg
s^{-1}. These results reconfirm the report by Mihara et al. (2004) using Ginga,
who observed a single absorption at ~16 keV in a minor (~10^{37} erg s^{-1})
outburst of this object. The luminosity-dependent cyclotron resonance energy
may be understood as a result of a decrease in the accretion column height, in
response to a decrease in the mass accretion rate. | astro-ph |
Astrometric asteroid masses: a simultaneous determination: Using over 89 million astrometric observations of 349,737 numbered minor
planets, an attempt was made to determine the masses of 230 of them by
simultaneously solving for corrections to all orbital elements and the masses.
For 132 minor planets an acceptable result was obtained, 50 of which appear to
be new. | astro-ph |
Evidence Against a Redshift z>6 for the Galaxy STIS 123627+621755: The identification of galaxies at extreme distances provides our most direct
information on the earliest phases of galaxy formation. The distance implied by
redshifts z > 5 makes this a challenging endeavor for even the most luminous
sources; interpretation of low signal-to-noise ratio observations of faint
galaxies is difficult and occasional misidentifications will occur. Here we
report on STIS 123627+621755, a galaxy with a suggested spectroscopic redshift
of z = 6.68 and the most distant spectroscopically-identified object claimed.
For the suggested redshift and reported spectral energy distribution, the
galaxy should be essentially invisible shortward of 9300 Angstroms because the
intervening intergalactic medium absorbs essentially all light energetic enough
to ionize neutral hydrogen (lambda < (1 + z) x 912 Angstroms; the redshifted
Lyman limit). The galaxy should be relatively bright in the near-infrared with
f(nu) ~ 1 microJy. Here we report a detection of the galaxy at 6700 Angstroms,
below the Lyman limit for z = 6.68. We also report a non-detection at 1.2
microns, implying the flux has dropped by a factor of three or more between
rest 1216 Angstroms and rest 1560 Angstroms for z = 6.68. Our observations are
inconsistent with the suggested extreme distance of STIS 123627+621755 and
conservatively require z < 6. | astro-ph |
BeppoSAX observations of the nearby low-mass X-ray binary and fast
transient SAX J1819.3-2525: SAX J1819.3-2525 is a nearby X-ray transient which exhibited a fast and large
X-ray outburst on Sep. 15, 1999 (Smith et al. 1999). The Wide Field Cameras and
the Narrow Field Instruments (NFI) on board BeppoSAX observed SAX J1819.3-2525
at various stages of its activity before that, in the spring and fall of 1999.
The fluxes range between 0.012 and 0.3 Crab units (2-10 keV). The NFI
observation is unique because it is the longest semi-continuous observation of
SAX J1819.3-2525 so far, and it offers a study of the spectrum at a relatively
high resolution of 8% full width at half maximum at 6 keV. We discuss the
observations with emphasis on the X-ray spectrum. A strong Fe-K emission line
was detected in SAX J1819.3-2525 with an equivalent width between 0.3 and 1
keV. The line energy is up to 6.85 +/- 0.02 keV and suggests the presence of
highly ionized iron. We identify this as fluorescent emission from a
photo-ionized plasma. The continuum spectrum is typical for a low-mass X-ray
binary in which emission from an accretion disk corona plays an important role.
There is no sign of an eclipse or periodic signal due to the binary orbit in
this exposure, despite the fact that the twin jets seen at radio wavelengths
suggest a high inclination angle. | astro-ph |
Optical-to-Near-Infrared Simultaneous Observations for the Hot Uranus
GJ3470b: A Hint for Cloud-free Atmosphere: We present optical (g', R_c, and I_c) to near-infrared (J) simultaneous
photometric observations for a primary transit of GJ3470b, a Uranus-mass
transiting planet around a nearby M dwarf, by using the 50-cm MITSuME telescope
and the 188-cm telescope, both at Okayama Astrophysical Observatory. From these
data, we derive the planetary mass, radius, and density as 14.1 \pm 1.3
M_earth, 4.32^{+0.21}_{-0.10} R_earth, and 0.94 \pm 0.12 g cm^{-3},
respectively, thus confirming the low density that was reported by Demory et
al. based on the Spitzer/IRAC 4.5-micron photometry (0.72^{+0.13}_{-0.12} g
cm^{-3}). Although the planetary radius is about 10% smaller than that reported
by Demory et al., this difference does not alter their conclusion that the
planet possesses a hydrogen-rich envelope whose mass is approximately 10% of
the planetary total mass. On the other hand, we find that the planet-to-star
radius ratio (R_p/R_s) in the J band (0.07577^{+0.00072}_{-0.00075}) is smaller
than that in the I_c (0.0802 \pm 0.0013) and 4.5-micron
(0.07806^{+0.00052}_{-0.00054}) bands by 5.9% \pm 2.0% and 3.0% \pm 1.2%,
respectively. A plausible explanation for the differences is that the planetary
atmospheric opacity varies with wavelength due to absorption and/or scattering
by atmospheric molecules. Although the significance of the observed R_p/R_s
variations is low, if confirmed, this fact would suggest that GJ3470b does not
have a thick cloud layer in the atmosphere. This property would offer a wealth
of opportunity for future transmission-spectroscopic observations of this
planet to search for certain molecular features, such as H2O, CH4, and CO,
without being prevented by clouds. | astro-ph |
Exploring the Variable Sky with LINEAR. I. Photometric Recalibration
with SDSS: We describe photometric recalibration of data obtained by the asteroid survey
LINEAR. Although LINEAR was designed for astrometric discovery of moving
objects, the dataset described here contains over 5 billion photometric
measurements for about 25 million objects, mostly stars. We use SDSS data from
the overlapping ~10,000 deg^2 of sky to recalibrate LINEAR photometry, and
achieve errors of 0.03 mag for sources not limited by photon statistics, with
errors of 0.2 mag at r~18. With its 200 observations per object on average,
LINEAR data provide time domain information for the brightest 4 magnitudes of
SDSS survey. At the same time, LINEAR extends the deepest similar wide-area
variability survey, the Northern Sky Variability Survey, by 3 mag. We briefly
discuss the properties of about 7,000 visually confirmed periodic variables,
dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary
stars, and analyze their distribution in optical and infra-red color-color
diagrams. The LINEAR dataset is publicly available from the SkyDOT website
(http://skydot.lanl.gov). | astro-ph |
Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase
Measurements of the Event Horizon Telescope: General relativistic magnetohydrodynamic (GRMHD) simulations of accretion
disks and jets associated with supermassive black holes show variability on a
wide range of timescales. On timescales comparable to or longer than the
gravitational timescale $t_G=GM/c^3$, variation may be dominated by orbital
dynamics of the inhomogeneous accretion flow. Turbulent evolution within the
accretion disk is expected on timescales comparable to the orbital period,
typically an order of magnitude larger than $t_G$. For Sgr A*, $t_G$ is much
shorter than the typical duration of a VLBI experiment, enabling us to study
this variability within a single observation. Closure phases, the sum of
interferometric visibility phases on a triangle of baselines, are particularly
useful for studying this variability. In addition to a changing source
structure, variations in observed closure phase can also be due to interstellar
scattering, thermal noise, and the changing geometry of projected baselines
over time due to Earth rotation. We present a metric that is able to
distinguish the latter two from intrinsic or scattering variability. This
metric is validated using synthetic observations of GRMHD simulations of Sgr
A*. When applied to existing multi-epoch EHT data of Sgr A*, this metric shows
that the data are most consistent with source models containing intrinsic
variability from source dynamics, interstellar scattering, or a combination of
those. The effects of black hole inclination, orientation, spin, and morphology
(disk or jet) on the expected closure phase variability are also discussed. | astro-ph |
Characterisation of pulsed Carbon fiber illuminators for FIR instrument
calibration: We manufactured pulsed illuminators emitting in the far infrared for the
Planck-HFI bolometric instrument ground calibrations. Specific measurements
have been conducted on these light sources, based on Carbon fibers, to
understand and predict their properties. We present a modelisation of the
temperature dependence of the thermal conductivity and the calorific
capacitance of the fibers. A comparison between simulations and bolometer data
is given, that shows the coherence of our model. Their small time constants,
their stability and their emission spectrum pointing in the submm range make
these illuminators a very usefull tool for calibrating FIR instruments. | astro-ph |
Inside-out or Outside-in: The topology of reionization in the
photon-starved regime suggested by Lyman-alpha forest data: We use a set of semi-numerical simulations based on Zel'dovich approximation,
friends-of-friends algorithm and excursion set formalism to generate
reionization maps of high dynamic range with a range of assumptions regarding
the distribution and luminosity of ionizing sources and the spatial
distribution of sinks for the ionizing radiation. We find that ignoring the
inhomogeneous spatial distribution of regions of high gas density where
recombinations are important -- as is often done in studies of this kind -- can
lead to misleading conclusions regarding the topology of reionization,
especially if reionization occurs in the photon-starved regime suggested by Lya
forest data. The inhomogeneous spatial distribution of recombinations
significantly reduces the mean free path of ionizing photons and the typical
size of coherently ionized regions. Reionization proceeds then much more as an
outside-in process. Low-density regions far from ionizing sources become
ionized before regions of high gas density not hosting sources of ionizing
radiation. The spatial distribution of sinks of ionization radiation also
significantly affects shape and amplitude the power spectrum of fluctuations of
21cm emission. The slope of the 21cm power spectrum as measured by upcoming
21cm experiments should be able to distinguish to what extent the topology of
reionization proceeds outside-in or inside-out while the evolution of the
amplitude of the power spectrum with increasing ionized mass fraction should be
sensitive to the spatial distribution and the luminosity of ionizing sources. | astro-ph |
The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages
(ASHES). X: Hot Gas Reveals Deeply Embedded Star Formation: Massive infrared dark clouds (IRDCs) are considered to host the earliest
stages of high-mass star formation. In particular, 70 $\mu$m dark IRDCs are the
colder and more quiescent clouds. At a scale of about 5000 au using
formaldehyde (H2CO) emission, we investigate the kinetic temperature of dense
cores in 12 IRDCs obtained from the pilot ALMA Survey of 70 $\mu$m dark
High-mass clumps in Early Stages (ASHES). Compared to 1.3 mm dust continuum and
other molecular lines, such as C18O and deuterated species, we find that H2CO
is mainly sensitive to low-velocity outflow components rather than to quiescent
gas expected in the early phases of star formation. The kinetic temperatures of
these components range from 26 to 300 K. The Mach number reaches about 15 with
an average value of about 4, suggesting that the velocity distribution of gas
traced by H2CO is significantly influenced by a supersonic non-thermal
component. In addition, we detect warm line emission from HC3N and OCS in 14
protostellar cores, which requires high excitation temperatures (Eu/k ~ 100 K).
These results show that some of the embedded cores in the ASHES fields are in
an advanced evolutionary stage, previously unexpected for 70 $\mu$m dark IRDCs. | astro-ph |
X-Rays Beware: The Deepest Chandra Catalogue of Point Sources in M31: This study represents the most sensitive Chandra X-ray point source catalogue
of M31. Using 133 publicly available Chandra ACIS-I/S observations totalling ~1
Ms, we detected 795 X-ray sources in the bulge, northeast, and southwest fields
of M31, covering an area of approximately 0.6 deg$^{2}$, to a limiting
unabsorbed 0.5-8.0 keV luminosity of $10^{34}$ erg/s. In the inner bulge, where
exposure is approximately constant, X-ray fluxes represent average values
because they were determined from many observations over a long period of time.
Similarly, our catalogue is more complete in the bulge fields since monitoring
allowed more transient sources to be detected. The catalogue was
cross-correlated with a previous XMM-Newton catalogue of M31's $D_{25}$
isophote consisting of 1948 X-ray sources, with only 979 within the field of
view of our survey. We found 387 (49%) of our Chandra sources (352 or 44%
unique sources) matched to within 5 arcsec of 352 XMM-Newton sources. Combining
this result with matching done to previous Chandra X-ray sources we detected
259 new sources in our catalogue. We created X-ray luminosity functions (XLFs)
in the soft (0.5-2.0 keV) and hard (2.0-8.0 keV) bands that are the most
sensitive for any large galaxy based on our detection limits.
Completeness-corrected XLFs show a break around $1.3\times10^{37}$ erg/s,
consistent with previous work. As in past surveys, we find the bulge XLFs are
flatter than the disk, indicating a lack of bright high-mass X-ray binaries in
the disk and an aging population of low-mass X-ray binaries in the bulge. | astro-ph |
Window function dependence of the novel mass function of primordial
black holes: We investigate the ambiguity of the novel mass function of primordial black
holes, which has succeeded in identifying the black hole mass in a given
configuration of fluctuations, due to the choice of window function of smoothed
density fluctuations. We find that while the window function dependence of the
exponential factor in the novel mass function is the same as the one in the
conventional mass function around the top-hat scale, the dependences are
different on other scales, which leads to the narrower mass function in the
novel formulation for some window functions. | astro-ph |
Toward a global model of the interactions in low-lying states of methyl
cyanide: rotational and rovibrational spectroscopy of the $v_4 = 1$ state and
tentative interstellar detection of the $v_4 = v_8 = 1$ state in Sgr B2(N): New and existing rotational spectra of methyl cyanide were analyzed to extend
the global model of low-lying vibrational states and their interactions to
$v_4=1$ at 920 cm$^{-1}$. The rotational spectra cover large portions of the
36$-$1439 GHz region and reach quantum numbers $J$ and $K$ of 79 and 16,
respectively. Information on the $K$ level structure of CH$_3$CN is obtained
from IR spectra. A spectrum of $2\nu_8$ around 717 cm$^{-1}$, analyzed in our
previous study, covered also the $\nu_4$ band. The assignments in this band
cover 880$-$952 cm$^{-1}$, attaining quantum numbers $J$ and $K$ of 61 and 13,
respectively.
The most important interaction of $v_4=1$ appears to be with $v_8=3$, $\Delta
K=0$, $\Delta l=+3$, a previously characterized anharmonic resonance. We report
new analyses of interactions with $\Delta K=-2$ and $\Delta l=+1$, with $\Delta
K=-4$ and $\Delta l=-1$, and with $\Delta K=-6$ and $\Delta l=-3$; these four
types of interactions connect all $l$ substates of $v_8=3$ in energy to
$v_4=1$. A known $\Delta K=-2$, $\Delta l=+1$ interaction with $v_7=1$ was also
analyzed, and investigations of the $\Delta K=+1$, $\Delta l=-2$ and $\Delta
K=+3$, $\Delta l=0$ resonances with $v_8=2$ were improved, as were interactions
between successive states with $v_8\le 3$, mainly through new $v_8\le 2$
rotational data.
A preliminary single state analysis of the $v_4=v_8=1$ state was carried out
based on rotational transition frequencies and on $\nu_4+\nu_8-\nu_8$ hot band
data. A considerable fraction of the $K$ levels was reproduced within
uncertainties in its entirety or in part, despite obvious widespread
perturbations in $v_4=v_8=1$.
We detect rotational transitions of methyl cyanide from within all
vibrational states up to $v_4=1$ and $v_4=v_8=1$ tentatively toward the hot
molecular core of Sagittarius B2(N) employing the Atacama Large Millimeter
Array. | astro-ph |
Matching Radio Catalogs with Realistic Geometry: Application to SWIRE
and ATLAS: Crossmatching catalogs at different wavelengths is a difficult problem in
astronomy, especially when the objects are not point-like. At radio wavelengths
an object can have several components corresponding, for example, to a core and
lobes. {Considering not all radio detections correspond to visible or infrared
sources, matching these catalogs can be challenging.} Traditionally this is
done by eye for better quality, which does not scale to the large data volumes
expected from the next-generation of radio telescopes. We present a novel
automated procedure, using Bayesian hypothesis testing, to achieve reliable
associations by explicit modelling of a particular class of radio-source
morphology. {The new algorithm not only assesses the likelihood of an
association between data at two different wavelengths, but also tries to assess
whether different radio sources are physically associated, are double-lobed
radio galaxies, or just distinct nearby objects.} Application to the SWIRE and
ATLAS CDF-S catalogs shows that this method performs well without human
intervention. | astro-ph |
ALMA observations of cold molecular gas filaments trailing rising radio
bubbles in PKS0745-191: We present ALMA observations of the CO(1-0) and CO(3-2) line emission tracing
filaments of cold molecular gas in the central galaxy of the cluster
PKS0745-191. The total molecular gas mass of 4.6 +/- 0.3 x 10^9 solar masses,
assuming a Galactic X_{CO} factor, is divided roughly equally between three
filaments each extending radially 3-5 kpc from the galaxy centre. The emission
peak is located in the SE filament roughly 1 arcsec (2 kpc) from the nucleus.
The velocities of the molecular clouds in the filaments are low, lying within
+/-100 km/s of the galaxy's systemic velocity. Their FWHMs are less than 150
km/s, which is significantly below the stellar velocity dispersion. Although
the molecular mass of each filament is comparable to a rich spiral galaxy, such
low velocities show that the filaments are transient and the clouds would
disperse on <10^7 yr timescales unless supported, likely by the indirect effect
of magnetic fields. The velocity structure is inconsistent with a merger origin
or gravitational free-fall of cooling gas in this massive central galaxy. If
the molecular clouds originated in gas cooling even a few kpc from their
current locations their velocities would exceed those observed. Instead, the
projection of the N and SE filaments underneath X-ray cavities suggests they
formed in the updraft behind bubbles buoyantly rising through the cluster
atmosphere. Direct uplift of the dense gas by the radio bubbles appears to
require an implausibly high coupling efficiency. The filaments are coincident
with low temperature X-ray gas, bright optical line emission and dust lanes
indicating that the molecular gas could have formed from lifted warmer gas that
cooled in situ. | astro-ph |
Statistical Analysis of Filament Features Based on the Hα Solar
Images from 1988 to 2013 by Computer Automated Detection Method: We improve our filament automated detection method which was proposed in our
previous works. It is then applied to process the full disk H$\alpha$ data
mainly obtained by Big Bear Solar Observatory (BBSO) from 1988 to 2013,
spanning nearly 3 solar cycles. The butterfly diagrams of the filaments,
showing the information of the filament area, spine length, tilt angle, and the
barb number, are obtained. The variations of these features with the calendar
year and the latitude band are analyzed. The drift velocities of the filaments
in different latitude bands are calculated and studied. We also investigate the
north-south (N-S) asymmetries of the filament numbers in total and in each
subclass classified according to the filament area, spine length, and tilt
angle. The latitudinal distribution of the filament number is found to be
bimodal. About 80% of all the filaments have tilt angles within [0{\deg},
60{\deg}]. For the filaments within latitudes lower (higher) than 50{\deg} the
northeast (northwest) direction is dominant in the northern hemisphere and the
southeast (southwest) direction is dominant in the southern hemisphere. The
latitudinal migrations of the filaments experience three stages with declining
drift velocities in each of solar cycles 22 and 23, and it seems that the drift
velocity is faster in shorter solar cycles. Most filaments in latitudes lower
(higher) than 50{\deg} migrate toward the equator (polar region). The N-S
asymmetry indices indicate that the southern hemisphere is the dominant
hemisphere in solar cycle 22 and the northern hemisphere is the dominant one in
solar cycle 23. | astro-ph |
New Insights: the Accretion Process and Variable Wind from TW Hya: For the first time in a classical T Tauri star, we are able to trace an
accretion event signaled by an hour-long enhancement of X-rays from the
accretion shock and revealed through substantial sequential changes in optical
emission line profiles. Downflowing turbulent material appears in H-alpha and
H-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in
flux. Two hours after the X-ray accretion event, the optical veiling increases
due to continuum emission from the hot splashdown region. The response of the
stellar coronal emission to the heated photosphere follows about 2.4 hours
later, giving direct evidence that the stellar corona is heated in part by
accretion. Then, the stellar wind becomes re-established. A model that
incorporates the dynamics of this sequential series of events includes: an
accretion shock, a cooling downflow in a supersonically turbulent region,
followed by photospheric and later, coronal heating. This model naturally
explains the presence of broad optical and ultraviolet lines, and affects the
mass accretion rates currently determined from emission line profiles. These
results, coupled with the large heated coronal region revealed from X-ray
diagnostics, suggest that current models are not adequate to explain the
accretion process in young stars. | astro-ph |
Origin and Dynamical Evolution of Neptune Trojans - II: Long Term
Evolution: We present results examining the fate of the Trojan clouds produced in our
previous work. We find that the stability of Neptunian Trojans seems to be
strongly correlated to their initial post-migration orbital elements, with
those objects that survive as Trojans for billions of years displaying
negligible orbital evolution. The great majority of these survivors began the
integrations with small eccentricities (e < 0.2) and small libration amplitudes
(A < 30 - 40{\deg}). The survival rate of "pre-formed" Neptunian Trojans (which
in general survived on dynamically cold orbits (e < 0.1, i < 5 - 10{\deg}))
varied between ~5 and 70%. By contrast, the survival rate of "captured" Trojans
(on final orbits spread across a larger region of e-i element space) were
markedly lower, ranging between 1 and 10% after 4 Gyr. Taken in concert with
our earlier work, we note that planetary formation scenarios which involve the
slow migration (a few tens of millions of years) of Neptune from an initial
planetary architecture that is both resonant and compact (aN < 18 AU) provide
the most promising fit of those we considered to the observed Trojan
population. In such scenarios, we find that the current day Trojan population
would number ~1% of that which was present at the end of the planet's
migration, with the bulk being sourced from captured, rather than pre-formed
objects. We note, however, that even those scenarios still fail to reproduce
the currently observed portion of the Neptune Trojan population moving on
orbits with e < 0.1 but i > 20{\deg}. Dynamical integrations of the currently
observed Trojans show that five out of the seven are dynamically stable on 4
Gyr timescales, while 2001 QR322, exhibits significant dynamical instability.
The seventh Trojan object, 2008 LC18, has such large orbital uncertainties that
only future studies will be able to determine its stability. | astro-ph |
Accurate mass estimates from the proper motions of dispersion-supported
galaxies: Starting with the spherical Jeans equation, we show that there exists a
radius where the mass enclosed depends only on the projected tangential
velocity dispersion, assuming that the anisotropy profile slowly varies. This
is well-approximated at the radius where the log-slope of the stellar tracer
profile is $-2$: $r_{-2}$. The associated mass is $M(r_{-2}) = 2 G^{-1} \langle
\sigma_{\mathcal{T}}^{2}\rangle^{*} r_{-2}$ and the circular velocity is
$V^{2}({r_{-2}}) = 2\langle \sigma_{\mathcal{T}}^{2}\rangle^{*}$. For a Plummer
profile $r_{-2} \simeq 4R_e/5$. Importantly, $r_{-2}$ is smaller than the
characteristic radius for line-of-sight velocities derived by Wolf et al. 2010.
Together, the two estimators can constrain the mass profiles of
dispersion-supported galaxies. We illustrate its applicability using published
proper motion measurements of dwarf galaxies Draco and Sculptor, and find that
they are consistent with inhabiting cuspy NFW subhalos of the kind predicted in
CDM but we cannot rule out a core. We test our combined mass estimators against
previously-published, non-spherical cosmological dwarf galaxy simulations done
in both CDM and SIDM. For CDM, the estimates for the dynamic rotation curves
are found to be accurate to $10\%$ while SIDM are accurate to $15\%$.
Unfortunately, this level of accuracy is not good enough to measure slopes at
the level required to distinguish between cusps and cores of the type predicted
in viable SIDM models without stronger priors. However, we find that this
provides good enough accuracy to distinguish between the normalization
differences predicted at small radii ($r \simeq r_{-2} < r_{\rm core}$) for
interesting SIDM models. As the number of galaxies with internal proper motions
increases, mass estimators of this kind will enable valuable constraints on
SIDM and CDM models. | astro-ph |
Inferring the magnetic field vector in the quiet Sun. III. Disk
variation of the Stokes profiles and isotropism of the magnetic field: We have studied the angular distribution of the magnetic field vector in the
solar internetwork employing high-quality data (noise level $\sigma \approx
3\times 10^{-4}$ in units of the quiet-Sun intensity) at different latitudes
recorded with the Hinode/SP instrument. Instead of applying traditional
inversion codes of the radiative transfer equation to retrieve the magnetic
field vector at each spatial point on the solar surface and studying the
resulting distribution of the magnetic field vector, we surmised a theoretical
distribution function of the magnetic field vector and used it to obtain the
theoretical histograms of the Stokes profiles. These histograms were then
compared to the observed ones. Any mismatch between them was ascribed to the
theoretical distribution of the magnetic field vector, which was subsequently
modified to produce a better fit to the observed histograms. With this method
we find that Stokes profiles with signals above $2\times 10^{-3}$ (in units of
the continuum intensity) cannot be explained by an isotropic distribution of
the magnetic field vector. We also find that the differences between the
histograms of the Stokes profiles observed at different latitudes cannot be
explained in terms of line-of-sight effects. However, they can be explained by
a distribution of the magnetic field vector that inherently varies with
latitude. We note that these results are based on a series of assumptions that,
although briefly discussed in this paper, need to be considered in more detail
in the future. | astro-ph |
On the description of the GCR intensity in the last three solar minima: We discuss the main characteristic features in the heliospheric parameters
important for the GCR intensity modulation for the last three solar minima
(1986--1987, 1996--1997 and 2008--2009). The model for the GCR intensity
modulation is considered and the set of the model parameters is chosen which
allows the description of the observed GCR intensity distributions at the
moments of the maximum GCR intensity in two solar minima (1987 and 1997) normal
for the second half of the last century. Then we try to describe with the above
model and set of parameters the unusually soft GCR energy spectra at the
moments of the maximum GCR intensity in the last solar minimum between cycles
23 and 24 (2009). Our main conclusion is that the most simple way to do so is
to reduce the size of the modulation region and, probably, change the rigidity
dependence of the diffusion coefficient. The change of both parameters is
substantiated by the observations of the solar wind and heliospheric magnetic
field. | astro-ph |
The supercluster-void network V. Alternative evidence for its regularity: The distribution of Abell clusters of galaxies is analysed to study the
regularity of the supercluster-void network. A new geometric method sensitive
to the regularity of the location of clusters is applied. We find that the
supercluster-void network resembles a cubical lattice over the whole space
investigated. The distribution of rich superclusters is not isotropic: along
the main axis of the network it is periodic with a step of length about 130 Mpc
(for Hubble constant h=1), whereas along the diagonal of the network the period
is larger. This large-scale inhomogeneity is compatible with recent CMB data. | astro-ph |
Detection of heavy-metal lines in the spectrum of the circumstellar
envelope of a post-AGB star: Splitting of the strongest absorption lines with a lower-level excitation
potential $\chi<$1eV has been detected for the first time in the optical
spectra of the post-AGB star V354Lac obtained with a spectral resolution
R=60000 at the 6-m telescope BTA. Analysis of the kinematics shows that the
short-wavelength component of the split line originates in the star's thick
gas-dust envelope. Disregarding the splitting of strong lines when the chemical
composition is calculated leads to overestimated excess of s-process elements
(Ba, La, Ce, Nd) in the stellar atmosphere. The profiles of strong absorption
lines have been found to be variable. The available radial-velocity data
suggest the absence of any trend in the velocity field in the atmosphere and
circumstellar envelope of V354Lac over 15 years of its observations. | astro-ph |
Study of muons from ultra-high energy cosmic ray air showers measured
with the Telescope Array experiment: One of the uncertainties in interpretation of ultra-high energy cosmic ray
(UHECR) data comes from the hadronic interaction models used for air shower
Monte Carlo (MC) simulations. The number of muons observed at the ground from
UHECR-induced air showers is expected to depend upon the hadronic interaction
model. One may therefore test the hadronic interaction models by comparing the
measured number of muons with the MC prediction. In this paper, we present the
results of studies of muon densities in UHE extensive air showers obtained by
analyzing the signal of surface detector stations which should have high
$\it{muon \, purity}$. The muon purity of a station will depend on both the
inclination of the shower and the relative position of the station. In 7 years'
data from the Telescope Array experiment, we find that the number of particles
observed for signals with an expected muon purity of $\sim$65% at a lateral
distance of 2000 m from the shower core is $1.72 \pm 0.10{\rm (stat.)} \pm 0.37
{\rm (syst.)}$ times larger than the MC prediction value using the QGSJET II-03
model for proton-induced showers. A similar effect is also seen in comparisons
with other hadronic models such as QGSJET II-04, which shows a $1.67 \pm 0.10
\pm 0.36$ excess. We also studied the dependence of these excesses on lateral
distances and found a slower decrease of the lateral distribution of muons in
the data as compared to the MC, causing larger discrepancy at larger lateral
distances. | astro-ph |
When does an old nova become a dwarf nova? Kinematics and age of the
nova shell of the dwarf nova AT Cnc: The Z Cam-type dwarf nova AT Cnc displays a classical nova (CN) shell,
demonstrating that mass transfer in cataclysmic binaries decreases
substantially after a CN eruption. The hibernation scenario of cataclysmic
binaries predicts such a decrease, on a timescale of a few centuries. In order
to measure the time since AT Cnc's last CN eruption, we have measured the
radial velocities of a hundred clumps in its ejecta with SITELLE, CFHT's
recently commissioned imaging Fourier transform spectrometer. These range from
-455 to +490 km/s. Coupled with the known distance to AT Cnc of 460 pc (Shara
2012), the size of AT Cnc's shell, and a simple model of nova ejecta
deceleration, we determine that the last CN eruption of this system occurred
$330_{-90}^{+135}$ years ago. This is the most rapid transition from a high
mass transfer rate, novalike variable to a low mass transfer rate, dwarf nova
yet measured, and in accord with the hibernation scenario of cataclysmic
binaries. We conclude by noting the similarity in deduced outburst date (within
a century of 1686 CE) of AT Cnc with a "guest star" reported in the
constellation Cancer by Korean observers in 1645 CE. | astro-ph |
An updated catalogue of giant radio sources: We present a catalogue of 349 giant radio sources (GRSs including both
galaxies and quasars). The database contains all giants known to date from the
literature. These GRSs cover the redshift range of 0.016$<$z$<$3.22 and include
radio sources of projected linear sizes larger than 0.7~Mpc which extend up to
4.7~Mpc. We provide the principal parameters (i.e. exact position of the host
in the sky, redshift, angular and projected linear size, red optical magnitude,
radio morphology type, total radio flux density and luminosity) for all the
sources as well as characteristics of the sample. Based on the distribution of
GRSs in the sky we identify regions where there is a paucity of giants, so that
future surveys for this type of objects could concentrate primarily in these
fields. From the analysis presented here, we estimate a lower limit for the
expected number of GRSs as about 2000, for the resolution and sensitivity
limits of FIRST, NRAO VLA Sky Survey and Sloan Digital Sky Survey surveys.
Compared with earlier compilations, there is a significant increase in the
number of large giants with sizes $>$ 2 Mpc as well as those at high redshifts
with z$>$1. We discuss aspects of their evolution and suggest that these are
consistent with evolutionary models. | astro-ph |
Features of the inflaton potential and the power spectrum of
cosmological perturbations: We discuss features of the inflaton potential that can lead to a strong
enhancement of the power spectrum of curvature perturbations. We show that a
steep decrease of the potential induces an enhancement of the spectrum by
several orders of magnitude, which may lead to the production of primordial
black holes. The same feature can also create a distinctive oscillatory pattern
in the spectrum of gravitational waves generated through the scalar
perturbations at second order. We study the additive effect of several such
features. We analyse a simplified potential, but also discuss the possible
application to supergravity models. | astro-ph |
X Ray Precursors in SGRs: Precessing Gamma Jet Tails: Weak isolated X-ray precursor events before the main Gamma Ray Burst, GRB,
and also rare Soft Gamma Repeaters, SGR, events are in complete disagreement
with any Fireball, or Magnetar, one-shoot explosive scenarios. Fireball model
in last two years has been deeply modified into a fountain beamed Jet exploding
and interacting on external shells to explain GRB fine time structure. On the
contrary earlier we proposed a unified scenario for both GRBs-SGRs where a
precessing Gamma Jet (of different intensity) and its geometrical beaming is
the source of both GRB and SGRs wide morphology. GRBs are peaked SNs Jet
spinning and precessing observed along the thin Jet axis. Their mysterious weak
X precursors bursts, corresponding to non-negligible energy powers, up to
million Supernova ones for GRB, are gamma Jet tails beamed off-axis, observed
at X-Ray tails. They are rare, about (3-6)% of all GRBs, but not unique at all.
Comparable brief X-ray precursor flashes occurred in rarest and most detailed
SGRs events as the 27 and the 29 August 1998 event from SGR 1900+14. The same
source has been in very power-full activity on recent 18 April 2001 once again
preceded by X-Ray precursors. These events are inconsistent with any Fireball
or Magnetar-Mini-Fireball models. We interpret them naturally as earlier
marginal blazing of outlying X conical precessing Jet, an off-axis tails
surrounding a narrower gamma precessing Jet. Only when the light-house Jet is
in on-axis blazing mode toward the Earth we observe the harder power-full SGR
event. We predict such a rich X-Ray precursor signals (more numerous then gamma
ones) during Soft Gamma Repeater peak activities; they should be abundant and
within detection threshold by a permanent monitoring SGRs by Beppo-Sax WFC or
Chandra X ray satellites while at peak activity. | astro-ph |
A Critical Look at the Mass-Metallicity-SFR Relation in the Local
Universe. I. An Improved Analysis Framework and Confounding Systematics: It has been proposed that the mass-metallicity relation of galaxies exhibits
a secondary dependence on star formation rate (SFR), and that the resulting
M-Z-SFR relation may be redshift-invariant, i.e., "fundamental." However,
conflicting results on the character of the SFR dependence, and whether it
exists, have been reported. To gain insight into the origins of the conflicting
results, we (a) devise a non-parametric, astrophysically motivated analysis
framework based on the offset from the star-forming ("main") sequence at a
given stellar mass (relative specific SFR), (b) apply this methodology and
perform a comprehensive re-analysis of the local M-Z-SFR relation, based on
SDSS, GALEX, and WISE data, and (c) study the impact of sample selection, and
of using different metallicity and SFR indicators. We show that metallicity is
anti-correlated with specific SFR regardless of the indicators used. We do not
find that the relation is spurious due to correlations arising from biased
metallicity measurements, or fiber aperture effects. We emphasize that the
dependence is weak/absent for massive galaxies ($\log M_*>10.5$), and that the
overall scatter in the M-Z-SFR relation does not greatly decrease from the M-Z
relation. We find that the dependence is stronger for the highest SSFR galaxies
above the star-forming sequence. This two-mode behavior can be described with a
broken linear fit in 12+log(O/H) vs. log (SFR$/M_*$), at a given $M_*$.
Previous parameterizations used for comparative analysis with higher redshift
samples that do not account for the more detailed behavior of the local M-Z-SFR
relation may incorrectly lead to the conclusion that those samples follow a
different relationship. | astro-ph |
Massive Star Evolution and Nucleosynthesis -Lower End of Fe-Core
Collapse Supernova Progenitors and Remnant Neutron Star Mass Distribution-: In order to explore various aspects of stellar evolution, supernovae, gamma
ray bursts and nucleosynthesis, we have developed a new efficient stellar
evolution code. In this paper we describe this new code and compare the results
with the ones calculated by the previous code. Specifically we focus on the
progenitor evolution of lower end of the Fe-core collapse supernovae, and mass
distribution of remnant neutron stars. We describe how different assumptions
will lead different neutron star mass distribution. We also review recent works
of our research group. | astro-ph |
Impact of Scale Dependent Bias and Nonlinear Structure Growth on the ISW
Effect: Angular Power Spectra: We investigate the impact of nonlinear evolution of the gravitational
potentials in the LCDM model on the Integrated Sachs-Wolfe (ISW) contribution
to the CMB temperature power spectrum, and on the cross-power spectrum of the
CMB and a set of biased tracers of the mass. We use an ensemble of N-body
simulations to directly follow the potentials and compare results to
perturbation theory (PT). The predictions from PT match the results to high
precision for k<0.2 h/Mpc. We compute the nonlinear corrections to the angular
power spectrum and find them to be <10% of linear theory for l<100. These
corrections are swamped by cosmic variance. On scales l>100 the departures are
more significant, however the CMB signal is more than a factor 10^3 larger at
this scale. Nonlinear ISW effects therefore play no role in shaping the CMB
power spectrum for l<1500. We analyze the CMB--density tracer cross-spectrum
using simulations and renormalized bias PT, and find good agreement. The usual
assumption is that nonlinear evolution enhances the growth of structure and
counteracts linear ISW on small scales, leading to a change in sign of the
CMB-LSS cross-spectrum at small scales. However, PT analysis suggests that this
trend reverses at late times when the logarithmic growth rate
f(a)=dlnD/dlna<0.5 or om_m(a)<0.3. Numerical results confirm these expectations
and we find no sign change in ISW-LSS cross-power for low redshifts.
Corrections due to nonlinearity and scale dependence of the bias are found to
be <10% for l<100, therefore below the S/N of the current and future
measurements. Finally, we estimate the CMB--halo cross-correlation coefficient
and show that it can be made to match that for CMB--dark matter to within 5%
for thin redshift shells, mitigating the need to model bias evolution. | astro-ph |
3D Smoothed Particle Hydrodynamics Models of Betelgeuse's Bow Shock: Betelgeuse, the bright red supergiant (RSG) in Orion, is a runaway star. Its
supersonic motion through the interstellar medium has resulted in the formation
of a bow shock, a cometary structure pointing in the direction of motion. We
present the first 3D hydrodynamic simulations of the formation and evolution of
Betelgeuse's bow shock. We show that the bow shock morphology depends
substantially on the growth timescale for Rayleigh-Taylor versus
Kelvin-Helmholtz instabilities. We discuss our models in light of the recent
Herschel, GALEX and VLA observations. If the mass in the bow shock shell is low
(~few x 0.001 Msun), as seems to be implied by the AKARI and Herschel
observations, then Betelgeuse's bow shock is very young and is unlikely to have
reached a steady state. The circular, smooth bow shock shell is consistent with
this conclusion. We further discuss the implications of our results, in
particular, the possibility that Betelgeuse may have only recently entered the
RSG phase. | astro-ph |
Temperature-dependent oscillation modes in rotating superfluid neutron
stars: We calculate the spectrum of inertial oscillation modes in a slowly rotating
superfluid neutron star, including, for the first time, both the effects of
finite temperatures and entrainment between superfluid neutrons and protons. We
work in the Newtonian limit and assume minimal core composition (neutrons,
protons and electrons). We also developed an approximate method that allows one
to calculate the superfluid r-mode analytically. Finally, we derive and analyze
dispersion relations for inertial modes in the superfluid NS matter in the
short wavelength limit. | astro-ph |
Chromaticity in all-reflective telescopes for astrometry: Chromatic effects are usually associated with refractive optics, so
reflective telescopes are assumed to be free from them. We show that
all-reflective optics still bears significant levels of such perturbations,
which is especially critical to modern micro-arcsecond astrometric experiments.
We analyze the image formation and measurement process to derive a precise
definition of the chromatic variation of the image position, and we evaluate
the key aspects of optical design with respect to chromaticity. The fundamental
requirement related to chromaticity is the symmetry of the optical design and
of the wavefront errors. Finally, we address some optical engineering issues,
such as manufacturing and alignment, providing recommendations to minimize the
degradation that chromaticity introduces into astrometry. | astro-ph |
Confirmation of double peaked Lyman-alpha emission at z=6.593:
Witnessing a galaxy directly contributing to the reionisation of the Universe: Distant luminous Lyman-alpha emitters (LAEs) are excellent targets for
spectroscopic observations of galaxies in the epoch of reionisation (EoR). We
present deep high-resolution (R=5000) VLT/X-SHOOTER observations, along with an
extensive collection of photometric data of `COLA1', a proposed double peaked
LAE at z=6.6 (Hu et al. 2016). We rule out that COLA1's emission line is an
[OII] doublet at z=1.475 on the basis of i) the asymmetric red line-profile and
flux ratio of the peaks (blue/red=$0.31\pm0.03$) and ii) an unphysical [OII]/Ha
ratio ([OII]/Ha > 22). We show that COLA1's observed B-band flux is explained
by a faint extended foreground LAE, for which we detect Lya and [OIII] at
z=2.142. We thus conclude that COLA1 is a real double-peaked LAE at z=6.593,
the first discovered at z>6, confirming the result from Hu et al. (2016). COLA1
is UV luminous (M$_{1500}=-21.6\pm0.3$), has a high equivalent width
(EW$_{0}$~120 \AA) and very compact Lya emission (r$_{50} = 0.3$ kpc).
Relatively weak inferred Hb+[OIII] line-emission from Spitzer/IRAC indicates an
extremely low metallicity of Z<1/20 Z$_{\odot}$ or reduced strength of nebular
lines due to high escape of ionising photons. The small Lya peak separation of
$220\pm20$ km/s implies a low HI column density and an ionising photon escape
fraction of ~15-30 %, providing the first direct evidence that such galaxies
contribute actively to the reionisation of the Universe at z>6. Based on simple
estimates, we find that COLA1 could have provided just enough photons to
reionise its own ~0.3 pMpc bubble, allowing the blue Lya line to be observed.
However, we also discuss alternative scenarios explaining the detected double
peaked nature of COLA1. Our results show that future high-resolution
observations of statistical samples of double peaked LAEs at z>5 are a
promising probe of the occurrence of ionised regions around galaxies in the
EoR. | astro-ph |
Instability of a stalled accretion shock: evidence for the
advective-acoustic cycle: We analyze the linear stability of a stalled accretion shock in a perfect gas
with a parametrized cooling function L ~ rho^{beta-alpha} P^alpha. The
instability is dominated by the l=1 mode if the shock radius exceeds 2-3 times
the accretor radius, depending on the parameters of the cooling function. The
growth rate and oscillation period are comparable to those observed in the
numerical simulations of Blondin & Mezzacappa (2006). The instability mechanism
is analyzed by separately measuring the efficiencies of the purely acoustic
cycle and the advective-acoustic cycle. These efficiencies are estimated
directly from the eigenspectrum, and also through a WKB analysis in the high
frequency limit. Both methods prove that the advective-acoustic cycle is
unstable, and that the purely acoustic cycle is stable. Extrapolating these
results to low frequency leads us to interpret the dominant mode as an
advective-acoustic instability, different from the purely acoustic
interpretation of Blondin & Mezzacappa (2006). A simplified characterization of
the instability is proposed, based on an advective-acoustic cycle between the
shock and the radius r_nabla where the velocity gradients of the stationary
flow are strongest. The importance of the coupling region in this mechanism
calls for a better understanding of the conditions for an efficient
advective-acoustic coupling in a decelerated, nonadiabatic flow, in order to
extend these results to core-collapse supernovae. | astro-ph |
The orbital period of the recurrent X-ray transient in Terzan 6: Four or five new outbursts were detected of the bright X-ray transient GRS
1747-312 in the globular cluster Terzan 6 between 1996 and 1999, through
monitoring campaigns with the Wide Field Cameras (WFCs) on BeppoSAX and the
Proportional Counter Array (PCA) on RossiXTE. This is the first time that the
source is seen to exhibit recurrent outbursts after the discovery in September
1990 with ART-P on Granat. Three target-of-opportunity observations in 1998 and
1999, with the narrow-field instruments on BeppoSAX and the PCA, revealed one
sharp drop in the flux which we identify as an eclipse of the compact X-ray
source by the companion star. A detailed analysis of WFC data identifies
further eclipses and we measure the orbital period at 12.360+/-0.009 hr. This
is consistent with an identification as a low-mass X-ray binary, as suggested
already by the association with a globular cluster. The eclipse duration is
0.72+/-0.06 hr. This implies that the inclination angle is larger than 74 deg.
The 0.1-200 keV unabsorbed peak luminosity is 7X10^36 erg/s. The nature of the
compact object is unclear. | astro-ph |
Diagnostics for specific PAHs in the far-IR: searching neutral
naphthalene and anthracene in the Red Rectangle: Context. In the framework of the interstellar polycyclic aromatic
hydrocarbons (PAHs) hypothesis, far-IR skeletal bands are expected to be a
fingerprint of single species in this class. Aims. We address the question of
detectability of low energy PAH vibrational bands, with respect to spectral
contrast and intensity ratio with ``classical'' Aromatic Infrared Bands (AIBs).
Methods. We extend our extablished Monte-Carlo model of the photophysics of
specific PAHs in astronomical environments, to include rotational and
anharmonic band structure. The required molecular parameters were calculated in
the framework of the Density Functional Theory. Results. We calculate the
detailed spectral profiles of three low-energy vibrational bands of neutral
naphthalene, and four low-energy vibrational bands of neutral anthracene. They
are used to establish detectability constraints based on intensity ratios with
``classical'' AIBs. A general procedure is suggested to select promising
diagnostics, and tested on available Infrared Space Observatory data for the
Red Rectangle nebula. Conclusions. The search for single, specific PAHs in the
far-IR is a challenging, but promising task, especially in view of the
forthcoming launch of the Herschel Space Observatory. | astro-ph |
On mass distribution of coalescing black holes: Available data on the chirp mass distribution of the coalescing black hole
binaries in O1-O3 LIGO/Virgo runs are analyzed and compared statistically with
the distribution calculated under the assumption that these black holes are
primordial with a log-normal mass spectrum. The theoretically calculated chirp
mass distribution with the inferred best acceptable mass spectrum parameters,
$M_0=17 M_\odot$ and $\gamma=0.9$, perfectly describes the data. The value of
$M_0$ very well agrees with the theoretically expected one. On the opposite,
the chirp mass distribution of black hole binaries originated from massive
binary star evolution requires additional model adjustments to reproduce the
observed chirp mass distribution | astro-ph |
A New Numerical Method for Solving Radiation Driven Winds from Hot Stars: We present a general method for solving the non--linear differential equation
of monotonically increasing steady--state radiation driven winds. We
graphically identify all the singular points before transforming the momentum
equation to a system of differential equations with all the gradients
explicitly give. This permits a topological classification of all singular
points and to calculate the maximum and minimum mass--loss of the wind. We use
our method to analyse for the first time the topology of the non--rotating
frozen in ionisation m--CAK wind, with the inclusion of the finite disk
correction factor and find up to 4 singular points, three of the x--type and
one attractor--type. The only singular point (and solution passing through)
that satisfies the boundary condition at the stellar surface is the standard
m--CAK singular point. | astro-ph |
A Large Scale, Low Frequency Murchison Widefield Array Survey of
Galactic HII regions between 260< l <\340: We have compiled a catalogue of HII regions detected with the Murchison
Widefield Array (MWA) between 72 and 231MHz. The multiple frequency bands
provided by the MWA allow us identify the characteristic spectrum generated by
the thermal Bremsstrahlung process in HII regions. We detect 302 HII regions
between 260 < l < 340 and report on the positions, sizes, peak, integrated flux
density, and spectral indices of these HII regions. By identifying the point at
which HII regions transition from the optically thin to thick regime we derive
the physical properties including the electron density, ionised gas mass and
ionising photon flux, towards 61 HII regions. This catalogue of HII regions
represents the most extensive and uniform low frequency survey of HII regions
in the Galaxy to date. | astro-ph |
Mass-sheet degeneracy, power-law models and external convergence: Impact
on the determination of the Hubble constant from gravitational lensing: The light travel time differences in strong gravitational lensing systems
allows an independent determination of the Hubble constant. This method has
been successfully applied to several lens systems. The formally most precise
measurements are, however, in tension with the recent determination of $H_0$
from the Planck satellite for a spatially flat six-parameters $\Lambda CDM$
cosmology. We reconsider the uncertainties of the method, concerning the mass
profile of the lens galaxies, and show that the formal precision relies on the
assumption that the mass profile is a perfect power law. Simple analytical
arguments and numerical experiments reveal that mass-sheet like transformations
yield significant freedom in choosing the mass profile, even when exquisite
Einstein rings are observed. Furthermore, the characterization of the
environment of the lens does not break that degeneracy which is not physically
linked to extrinsic convergence. We present an illustrative example where the
multiple imaging properties of a composite (baryons + dark matter) lens can be
extremely well reproduced by a power-law model having the same velocity
dispersion, but with predictions for the Hubble constant that deviate by $\sim
20%$. Hence we conclude that the impact of degeneracies between parametrized
models have been underestimated in current $H_0$ measurements from lensing, and
need to be carefully reconsidered. | astro-ph |
Luminosity versus Rotation in a Supermassive Star: We determine the effect of rotation on the luminosity of supermassive stars.
We apply the Roche model to calculate analytically the emitted radiation from a
uniformly rotating, radiation-dominated supermassive configuration. We find
that the luminosity at maximum rotation, when mass at the equator orbits at the
Kepler period, is reduced by ~36% below the usual Eddington luminosity from the
corresponding nonrotating star. A supermassive star is believed to evolve in a
quasistationary manner along such a maximally rotating ``mass-shedding''
sequence before reaching the point of dynamical instability; hence this reduced
luminosity determines the evolutionary timescale. Our result therefore implies
that the lifetime of a supermassive star prior to dynamical collapse is ~56%
longer than the value typically estimated by employing the usual Eddington
luminosity. | astro-ph |
The Li dip : a probe of angular momentum transport in low mass stars: We use the measures of Li and rotational velocities in F Hyades stars to
assess the role of the wind-driven meridian circulation and of shear turbulence
in the transport of angular momentum in stars of different masses. Our models
include both element segregation and rotation-induced mixing, and we treat
simultaneously the transport of matter and angular momentum as described by
Zahn (1992) and Maeder (1995).
We show that the hot side of the Li dip in the Hyades is well explained
within this framework, which was also successfully used to reproduce the C and
N anomalies in B type stars (Talon et al. 1997). On the cool side of the dip,
another mechanism must participate in the transport of angular momentum; its
efficiency is linked to the depth of the surface convection zone. That
mechanism should also be responsible for the Sun's flat rotation profile. | astro-ph |
Synchrotron Outbursts in Galactic and Extra-galactic Jets, Any
Difference?: We discuss differences and similarities between jets powered by super-massive
black holes in quasars and by stellar-mass black holes in microquasars. The
comparison is based on multi-wavelength radio-to-infrared observations of the
two active galactic nuclei 3C 273 and 3C 279, as well as the two galactic
binaries GRS 1915+105 and Cyg X-3. The physical properties of the jet are
derived by fitting the parameters of a shock-in-jet model simultaneously to all
available observations. We show that the variable jet emission of galactic
sources is, at least during some epochs, very similar to that of extra-galactic
jets. As for quasars, their observed variability pattern can be well reproduced
by the emission of a series of self-similar shock waves propagating down the
jet and producing synchrotron outbursts. This suggests that the physical
properties of relativistic jets is independent of the mass of the black hole. | astro-ph |
Parallel Programming with MatlabMPI: MatlabMPI is a Matlab implementation of the Message Passing Interface (MPI)
standard and allows any Matlab program to exploit multiple processors.
MatlabMPI currently implements the basic six functions that are the core of the
MPI point-to-point communications standard. The key technical innovation of
MatlabMPI is that it implements the widely used MPI ``look and feel'' on top of
standard Matlab file I/O, resulting in an extremely compact (~100 lines) and
``pure'' implementation which runs anywhere Matlab runs. The performance has
been tested on both shared and distributed memory parallel computers. MatlabMPI
can match the bandwidth of C based MPI at large message sizes. A test image
filtering application using MatlabMPI achieved a speedup of ~70 on a parallel
computer. | astro-ph |
Hunting for anti-solar differentially rotating stars using the Rossby
number -- An application to the Kepler field: Anti-solar differential rotation profiles have been found for decades in
numerical simulations of convective envelopes of solar-type stars. These
profiles are characterized by a slow equator and fast poles (i.e., reversed
with respect to the Sun) and have been found in simulations for high Rossby
numbers (slow rotators). Rotation profiles like this have been reported
observationally in evolved stars, but have never been unambiguously observed
for cool solar-type stars on the main sequence. In this context, detecting this
regime in main-sequence solar-type stars would improve our understanding of
their magnetorotational evolution. The goal of this study is to identify the
most promising cool main-sequence stellar candidates for anti-solar
differential rotation in the \textit{Kepler} sample. First, we introduce a new
theoretical formula to estimate fluid Rossby numbers, $Ro_{\rm f}$, of
main-sequence solar-type stars, from observational quantities, and taking the
influences of the internal structure and metallicity into account. We obtain a
list of the most promising stars that are likely to show anti-solar
differential rotation. We identify two samples: one at solar metallicity,
including 14 targets, and another for other metallicities, including 8 targets.
We find that the targets with the highest $Ro_{\rm f}$ are likely to be early-G
or late-F stars at about log$_{10}g=4.37$~dex. We conclude that cool
main-sequence stellar candidates for anti-solar differential rotation exist in
the \textit{Kepler} sample. The most promising candidate is KIC~10907436, and
two other particularly interesting candidates are the solar analog KIC~7189915
and the seismic target KIC~12117868. Future characterization of these 22 stars
is expected to help us understand how dynamics can impact magnetic and
rotational evolution of old solar-type stars at high Rossby number. | astro-ph |
Probing the reach of the Intermediate Polar Cataclysmic Variable
Population with Swift J183920.1-045350: We report on the Swift/XRT Deep Galactic Plane Survey discovery and
multi-wavelength follow-up observations of a new intermediate polar Cataclysmic
Variable, Swift J183920.1-045350. A 449.7 s spin period is found in Xmm-Newton
and NuSTAR data, accompanied by a 459.9 s optical period that is most likely
the synodic, or beat period, produced from a 5.6 h orbital period. The orbital
period is seen with moderate significance in independent long-baseline optical
photometry observations with ZTF and SAAO. We find that the source X-ray pulsed
fraction decreases with increasing energy. The X-ray spectra are consistent
with the presence of an Fe emission line complex with both local and
interstellar absorption. In the optical spectra, strong H$\alpha{}$, H I, He I
and He II emission lines are observed, all common features in magnetic CVs. The
source properties are thus typical of known intermediate polars, with the
exception of its estimated distance of 2.26$^{+1.93}_{-0.83}$ kpc, which is
larger than typical, extending the reach of the CV population in our Galaxy. | astro-ph |
The dual origin of the nitrogen deficiency in comets: selective volatile
trapping in the nebula and postaccretion radiogenic heating: We propose a scenario that explains the apparent nitrogen deficiency in
comets in a way consistent with the fact that the surfaces of Pluto and Triton
are dominated by nitrogen-rich ice. We use a statistical thermodynamic model to
investigate the composition of the successive multiple guest clathrates that
may have formed during the cooling of the primordial nebula from the most
abundant volatiles present in the gas phase. These clathrates agglomerated with
the other ices (pure condensates or stoichiometric hydrates) and formed the
building blocks of comets. We report that molecular nitrogen is a poor
clathrate former, when we consider a plausible gas phase composition of the
primordial nebula. This implies that its trapping into cometesimals requires a
low disk temperature ($\sim$20 K) in order to allow the formation of its pure
condensate. We find that it is possible to explain the lack of molecular
nitrogen in comets as a consequence of their postformation internal heating
engendered by the decay of short-lived radiogenic nuclides. This scenario is
found consistent with the presence of nitrogen-rich ice covers on Pluto and
Triton. Our model predicts that comets should present xenon-to-water and
krypton-to-water ratios close to solar xenon-to-oxygen and krypton-to-oxygen
ratios, respectively. In contrast, the argon-to-water ratio is predicted to be
depleted by a factor of $\sim$300 in comets compared to solar argon-to-oxygen,
as a consequence of poor trapping efficiency and radiogenic heating. | astro-ph |
Statistics of Photospheric Supergranular Cells Observed by SDO/HMI: Aims: The statistics of the photospheric granulation pattern are investigated
using continuum images observed by Solar Dynamic Observatory (SDO)/Helioseismic
and Magnetic Imager (HMI) taken at 6713~\AA.
Methods: The supergranular boundaries can be extracted by tracking
photospheric velocity plasma flows. The local ball-tracking method is employed
to apply on the HMI data gathered over the years 2011-2015 to estimate the
boundaries of the cells. The edge sharpening techniques are exerted on the
output of ball-tracking to precisely identify the cells borders. To study the
fractal dimensionality (FD) of supergranulation, the box counting method is
used.
Results: We found that both the size and eccentricity follow the log-normal
distributions with peak values about 330 Mm$^2$ and 0.85, respectively. The
five-year mean value of the cells number appeared in half-hour sequences is
obtained to be about 60 $\pm$ 6 within an area of
$350^{\prime\prime}\times350^{\prime\prime}$. The cells orientation
distribution presents the power-law behavior.
Conclusions: The orientation of supergranular cells ($O$) and their size
($S$) follows a power-law function as $|O| \propto S^{9.5}$. We found that the
non-roundish cells with smaller and larger sizes than 600 Mm$^2$ are aligned
and perpendicular with the solar rotational velocity on the photosphere,
respectively. The FD analysis shows that the supergranular cells form the
self-similar patterns. | astro-ph |
A search for technosignatures from 14 planetary systems in the Kepler
field with the Green Bank Telescope at 1.15-1.73 GHz: Analysis of Kepler mission data suggests that the Milky Way includes billions
of Earth-like planets in the habitable zone of their host star. Current
technology enables the detection of technosignatures emitted from a large
fraction of the Galaxy. We describe a search for technosignatures that is
sensitive to Arecibo-class transmitters located within ~420 ly of Earth and
transmitters that are 1000 times more effective than Arecibo within ~13 000 ly
of Earth. Our observations focused on 14 planetary systems in the Kepler field
and used the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank
Telescope. Each source was observed for a total integration time of 5 minutes.
We obtained power spectra at a frequency resolution of 3 Hz and examined
narrowband signals with Doppler drift rates between +/-9 Hz/s. We flagged any
detection with a signal-to-noise ratio in excess of 10 as a candidate signal
and identified approximately 850 000 candidates. Most (99%) of these candidate
signals were automatically classified as human-generated radio-frequency
interference (RFI). A large fraction (>99%) of the remaining candidate signals
were also flagged as anthropogenic RFI because they have frequencies that
overlap those used by global navigation satellite systems, satellite downlinks,
or other interferers detected in heavily polluted regions of the spectrum. All
19 remaining candidate signals were scrutinized and none were attributable to
an extraterrestrial source. | astro-ph |
Determination of electron density and filling factor for soft X-ray
flare kernels: In a standard method of determining electron density for soft X-ray (SXR)
flare kernels it is necessary to assume what is the extension of a kernel along
the line of sight. This is a source of significant uncertainty of the obtained
densities. In our previous paper (Bak-Steslicka and Jakimiec, 2005) we have
worked out another method of deriving electron density, in which it is not
necessary to assume what is the extension of a kernel along the line of sight.
The point is that many flares, during their decay phase, evolve along the
sequence of steady-state models [quasi-steady-state (QSS) evolution] and then
the scaling law, derived for steady-state models, can be used to determine the
electron density. The aim of the present paper is: (1) to improve the two
methods of density determination, (2) to compare the densities obtained with
the two methods. We have selected a number of flares which showed QSS evolution
during the decay phase. For these flares the electron density, N, has been
derived by means of standard method and with our QSS method. Comparison of the
N values obtained with the two different methods allowed us: (1) to test the
obtained densities, (2) to evaluate the volume filling factor of the SXR
emitting plasma. Generally, we have found good agreement (no large systematic
difference) between the values of electron density obtained with the two
methods, but for some cases the values can differ by a factor up to 2. For most
flare kernels estimated filling factor turned out to be about 1, near the flare
maximum. | astro-ph |
Radio AGN in nearby dwarf galaxies: the important role of AGN in
dwarf-galaxy evolution: We combine deep optical and radio data, from the Hyper Suprime-Cam and the
Low-Frequency Array (LOFAR) respectively, to study 78 radio AGN in nearby
(z<0.5) dwarf galaxies. Comparison to a control sample, matched in stellar mass
and redshift, indicates that the AGN and controls reside in similar
environments, show similar star-formation rates (which trace gas availability)
and exhibit a comparable incidence of tidal features (which indicate recent
interactions). We explore the AGN properties by combining the predicted gas
conditions in dwarfs from a cosmological hydrodynamical simulation with a
Monte-Carlo suite of simulated radio sources, based on a semi-analytical model
for radio-galaxy evolution. In the subset of LOFAR-detectable simulated
sources, which have a similar distribution of radio luminosities as our
observed AGN, the median jet powers, ages and accretion rates are $\sim
10^{35}$ W, $\sim 5$ Myr and $\sim 10^{-3.4}$ M$_{\odot}$ yr$^{-1}$
respectively. The median mechanical energy output of these sources is $\sim100$
times larger than the median binding energy expected in dwarf gas reservoirs,
making AGN feedback plausible. Since special circumstances (in terms of
environment, gas availability and interactions) are not necessary for the
presence of AGN, and the central gas masses are predicted to be an order of
magnitude larger than that required to fuel the AGN, AGN triggering in dwarfs
is likely to be stochastic and a common phenomenon. Together with the
plausibility of energetic feedback, this suggests that AGN could be important
drivers of dwarf-galaxy evolution, as is the case in massive galaxies. | astro-ph |
Statistical characterization of polychromatic absolute and differential
squared visibilities obtained from AMBER/VLTI instrument: In optical interferometry, the visibility squared modulus are generally
assumed to follow a Gaussian distribution and to be independent of each other.
A quantitative analysis of the relevance of such assumptions is important to
help improving the exploitation of existing and upcoming multi-wavelength
interferometric instruments. Analyze the statistical behaviour of both the
absolute and the colour-differential squared visibilities: distribution laws,
correlations and cross-correlations between different baselines. We use
observations of stellar calibrators obtained with AMBER instrument on VLTI in
different instrumental and observing configurations, from which we extract the
frame-by-frame transfer function. Statistical hypotheses tests and diagnostics
are then systematically applied. For both absolute and differential squared
visibilities and under all instrumental and observing conditions, we find a
better fit for the Student distribution than for the Gaussian, log-normal and
Cauchy distributions. We find and analyze clear correlation effects caused by
atmospheric perturbations. The differential squared visibilities allow to keep
a larger fraction of data with respect to selected absolute squared
visibilities and thus benefit from reduced temporal dispersion, while their
distribution is more clearly characterized. The frame selection based on the
criterion of a fixed SNR value might result in either a biased sample of frames
or in a too severe selection. | astro-ph |
Gipsy 3D: Analysis, Visualization and Vo-Tools: The scientific goals of the AMIGA project are based on the analysis of a
significant amount of spectroscopic 3D data. In order to perform this work we
present an initiative to develop a new VO compliant package, including present
core applications and tasks offered by the Groningen Image Processing System
(GIPSY), and new ones based on use cases elaborated in collaboration with ad-
vanced users. One of the main goals is to provide local interoperability
between GIPSY (visualization and data analysis) and other VO software. The
connectivity with the Virtual Observatory environment will provide general
access to 3D data VO archives and services, maximizing the potential for
scientific discovery. | astro-ph |
Multi-wavelength analysis of the dust emission in the Small Magellanic
Cloud: We present an analysis of dust grain emission in the diffuse interstellar
medium of the Small Magellanic Cloud (SMC). This study is motivated by the
availability of 170 microns ISOPHOT data covering a large part of the SMC, with
a resolution enabling to disentangle the diffuse medium from the star forming
regions. After data reduction and subtraction of Galactic foreground emission,
we used the ISOPHOT data together with HiRes IRAS data and ATCA/Parkes combined
HI column density maps to determine dust properties for the diffuse medium. We
found a far infrared emissivity per hydrogen atom 30 times lower than the Solar
Neighborhood value. The modeling of the spectral energy distribution of the
dust, taking into account the enhanced interstellar radiation field, gives a
similar conclusion for the smallest grains (PAHs and very small grains)
emitting at shorter wavelength. Assuming Galactic dust composition in the SMC,
this result implies a difference in the gas-to-dust ratio (GDR) 3 times larger
than the difference in metallicity. This low depletion of heavy elements in
dust could be specific of the diffuse ISM and not apply for the whole SMC dust
if it results from efficient destruction of dust by supernovae explosions. | astro-ph |
The 2-10 keV emission properties of PSR B1937+21: We present the results of a BeppoSAX observation of the fastest pulsar known:
PSR B1937+21. The ~ 200 ks observation (78.5 (34) ks MECS (LECS) exposure
times) allowed us to investigate with high statistical significance both the
spectral properties and the pulse profile shape. The absorbed power law
spectral model gave a photon index of ~ 1.7 and N_H ~ 2.3 x 10^22 cm^-2. These
values explain both a) the ROSAT non-detection and b) the deviant estimate of a
photon index of ~ 0.8 obtained by ASCA. The pulse profile appears, for the
first time, clearly double peaked with the main component much stronger than
the other. The statistical significance is 10 sigma (main peak) and 5 sigma
(secondary peak). The 1.6-10 keV pulsed fraction is consistent with 100%; only
in the 1.6-4 keV band there is a ~ 2 sigma indication for a DC component. The
secondary peak is detected significantly only for energies above 3 / 4 keV. The
unabsorbed (2-10 keV) flux is F_2-10 = 3.7 x 10^-13 erg cm^-2 s^-1, implying a
luminosity of L_X = 4.6 x 10^31 Theta (d/3.6 kpc)^2 erg s^-1 and an X-ray
efficiency of eta = 4 x 10^-5 Theta, where Theta is the solid angle spanned by
the emission beam. These results are in agreement with those obtained by ASCA. | astro-ph |
WALLABY Pilot Survey: Public release of HI kinematic models for more
than 100 galaxies from phase 1 of ASKAP pilot observations: We present the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY)
Pilot Phase I HI kinematic models. This first data release consists of HI
observations of three fields in the direction of the Hydra and Norma clusters,
and the NGC 4636 galaxy group. In this paper, we describe how we generate and
publicly release flat-disk tilted-ring kinematic models for 109/592 unique HI
detections in these fields. The modelling method adopted here - which we call
the WALLABY Kinematic Analysis Proto-Pipeline (WKAPP) and for which the
corresponding scripts are also publicly available - consists of combining
results from the homogeneous application of the FAT and 3DBAROLO algorithms to
the subset of 209 detections with sufficient resolution and S/N in order to
generate optimized model parameters and uncertainties. The 109 models presented
here tend to be gas rich detections resolved by at least 3-4 synthesized beams
across their major axes, but there is no obvious environmental bias in the
modelling. The data release described here is the first step towards the
derivation of similar products for thousands of spatially-resolved WALLABY
detections via a dedicated kinematic pipeline. Such a large publicly available
and homogeneously analyzed dataset will be a powerful legacy product that that
will enable a wide range of scientific studies. | astro-ph |
BLR Modeling: A New Approach: We present a new scheme for modeling the broad line region in active galactic
nuclei. It involves photoionization calculations applied to a number of
variable emission lines at {\it all times}. We demonstrate how fitting all
lines simultaneously provide strong constraints on several of the more
important parameters, such as the density and column density, and the radial
distribution of the emission line clouds.
When applying the model to the Seyfert 1 galaxy NGC 5548, we are able to
reconstruct the light curves of four emission-lines, in time and in absolute
flux. We argue that the Balmer line light curves, and possibly also the MgII
light curve, do not fit this scheme because of the limitations of present-day
photoionization codes. We rule out models where the particle density scales as
r^{-2} and favor models where it scales as r^{-(1-1.5)}. We can place lower
limits on the column density at a distance of 10 ld, of N_{col}(r=10)>10^{22}
cm^{-2}, and limit the particle density to be in the range of
10^{11}>N(r=10)>10^{9.5} cm^{-3}. | astro-ph |
Grantecan spectroscopic observations and confirmations of Planetary
Nebulae candidates in the Northern Galactic Plane: We present Grantecan 10 m telescope (GTC) spectroscopic confirmations of 55
faint Planetary Nebulae (PNe) candidates discovered largely in the INT
Photometric H$_\alpha$ Survey of the Northern Galactic Plane (IPHAS) by our
pro-am collaboration. We confirm 46 of them as 'True' (T), 4 as 'Likely' (L)
and 5 as 'Possible' (P) PNe and including 5 new PNe central star (CSPN)
discoveries. This was from observations of 62 new candidates yielding a maximum
PN discovery success rate of 89%. The sensitivity and longer wavelength
coverage of IPHAS allows PNe to be found in regions of greater extinction and
at these lower Galactic latitudes, including PNe in a more advanced
evolutionary state and at larger distances compared to previously known
Galactic PNe. We use an holistic set of observed characteristics and optical
emission-line diagnostics to confirm candidates. Plasma properties have been
determined in a self-consistent way using PyNeb. This work is facilitated by
the functionality of our powerful, multi-wavelength database 'HASH' (Hong Kong,
Australian Astronomical Observatory, Strasbourg Observatory H-alpha Planetary
Nebula catalogue) that federates known imaging, spectroscopy and other
pertinent data for all Galactic T, L, P PNe and the significant numbers of
mimics. Reddenings, corrected radial velocities and PNe electron density and
temperature estimates are provided for these new PNe where possible. | astro-ph |
The chemical composition of the stellar cluster Gaia1: no surprise
behind Sirius: We observed 6 He-clump stars of the intermediate-age stellar cluster Gaia1
with the MIKE/MAGELLAN spectrograph. A possible extra-galactic origin of this
cluster, recently discovered thanks to the first data release of the ESA Gaia
mission, has been suggested, based on its orbital parameters. Abundances for
Fe, alpha, proton- and neutron-capture elements have been obtained. We find no
evidence of intrinsic abundance spreads. The iron abundance is solar
([FeI/H]=+0.00 +-0.01; sigma = 0.03 dex). All the other abundance ratios are,
by and large, solar-scaled, similar to the Galactic thin disk and open clusters
stars of similar metallicity. The chemical composition of Gaia1 does not
support an extra-galactic origin for this stellar cluster, that can be
considered as a standard Galactic open cluster. | astro-ph |
Space density of optically-selected type 2 quasars: Type 2 quasars are luminous active galactic nuclei (AGN) whose central
regions are obscured by large amounts of gas and dust. In this paper, we
present a catalog of type 2 quasars from the Sloan Digital Sky Survey (SDSS),
selected based on their optical emission lines. The catalog contains 887
objects with redshifts z < 0.83; this is six times larger than the previous
version and is by far the largest sample of type 2 quasars in the literature.
We derive the [OIII]5008 luminosity function for 10^8.3 Lsun < L[OIII] < 10^10
Lsun (corresponding to intrinsic luminosities up to M[2400A]-28 mag or
bolometric luminosities up to 4x10^47 erg/sec). This luminosity function
provides strong lower limits to the actual space density of obscured quasars,
due to our selection criteria, the details of the spectroscopic target
selection, as well as other effects. We derive the equivalent luminosity
function for the complete sample of type 1 (unobscured) quasars; then, we
determine the ratio of type 2/type 1 quasar number densities. Our best data
constrain this ratio to be at least 1.5:1 for 10^8.3 Lsun < L[OIII] < 10^9.5
Lsun at z < 0.3, and at least 1.2:1 for L[OIII]=10^10 Lsun at 0.3 < z < 0.83.
Type 2 quasars are at least as abundant as type 1 quasars in the relatively
nearby Universe (z < 0.8) for the highest luminosities. | astro-ph |
An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar
Medium: We present a survey of diffuse O VI emission in the interstellar medium
obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Spanning 5.5
years of FUSE observations, from launch through 2004 December, our data set
consists of 2925 exposures along 183 sight lines, including all of those with
previously-published O VI detections. The data were processed using an
implementation of CalFUSE v3.1 modified to optimize the signal-to-noise ratio
and velocity scale of spectra from an aperture-filling source. Of our 183 sight
lines, 73 show O VI 1032 emission, 29 at > 3-sigma significance. Six of the
3-sigma features have velocities |v_LSR| > 120 km/s, while the others have
|v_LSR| < 50 km/s. Measured intensities range from 1800 to 9100 LU, with a
median of 3300 LU. Combining our results with published O VI absorption data,
we find that an O VI-bearing interface in the local ISM yields an electron
density n_e = 0.2--0.3 cm^-3^ and a path length of 0.1 pc, while O VI-emitting
regions associated with high-velocity clouds in the Galactic halo have
densities an order of magnitude lower and path lengths two orders of magnitude
longer. Though the O VI intensities along these sight lines are similar, the
emission is produced by gas with very different properties. | astro-ph |
H$_2$O$_2$-induced Greenhouse Warming on Oxidized Early Mars: The existence of liquid water within an oxidized environment on early Mars
has been inferred by the Mn-rich rocks found during recent explorations on
Mars. The oxidized atmosphere implied by the Mn-rich rocks would basically be
comprised of CO$_2$ and H$_2$O without any reduced greenhouse gases such as
H$_2$ and CH$_4$. So far, however, it has been thought that early Mars could
not have been warm enough to sustain water in liquid form without the presence
of reduced greenhouse gases. Here, we propose that H$_2$O$_2$ could have been
the gas responsible for warming the surface of the oxidized early Mars. Our
one-dimensional atmospheric model shows that only 1 ppm of H$_2$O$_2$ is enough
to warm the planetary surface because of its strong absorption at far-infrared
wavelengths, in which the surface temperature could have reached over 273~K for
a CO$_2$ atmosphere with a pressure of 3~bar. A wet and oxidized atmosphere is
expected to maintain sufficient quantities of H$_2$O$_2$ gas in its upper
atmosphere due to its rapid photochemical production in slow condensation
conditions. Our results demonstrate that a warm and wet environment could have
been maintained on an oxidized early Mars, thereby suggesting that there may be
connections between its ancient atmospheric redox state and possible aqueous
environment. | astro-ph |
Search for dormant black holes in the OGLE data: Light curves of ellipsoidal variables collected by the Optical Gravitational
Lensing Experiment (OGLE) were analyzed, in order to search for dormant black
hole candidates. After the preselection based on the amplitude of ellipsoidal
modulation, each object was investigated by means of the spectral energy
distribution fit, which allowed us to select objects that are in close
agreement with the spectrum of a single stellar object. After this final step
of the preselection process, we were left with only fourteen objects that were
then investigated in detail. For each candidate, we estimated basic physical
parameters such as temperature, mass, luminosity, and, in some cases, radial
velocity semi-amplitude. One of the objects turned out to be a spotted star
while the rest are considered black-hole binary candidates. In the end, we
present an alternative explanation for the ellipsoidal modulation in the form
of contact binaries, which are not only vast in number, contrary to black-hole
binaries, but are also in much better agreement with the radial velocity
estimates for some of the systems analyzed. Even if the presented arguments
suggest a noncompact character of the companion objects, each of them should be
observed spectroscopically in order to verify the compact object hypothesis. | astro-ph |
Collisional Ionization Equilibrium for Optically Thin Plasmas. I.
Updated Recombination Rate Coefficients for Bare though Sodium-like Ions: Reliably interpreting spectra from electron-ionized cosmic plasmas requires
accurate ionization balance calculations for the plasma in question. However,
much of the atomic data needed for these calculations have not been generated
using modern theoretical methods and are often highly suspect. This translates
directly into the reliability of the collisional ionization equilibrium (CIE)
calculations. We make use of state-of-the-art calculations of dielectronic
recombination (DR) rate coefficients for the hydrogenic through Na-like ions of
all elements from He up to and including Zn. We also make use of
state-of-the-art radiative recombination (RR) rate coefficient calculations for
the bare through Na-like ions of all elements from H through to Zn. Here we
present improved CIE calculations for temperatures from $10^4$ to $10^9$ K
using our data and the recommended electron impact ionization data of
\citet{Mazz98a} for elements up to and including Ni and Mazzotta (private
communication) for Cu and Zn. DR and RR data for ionization stages that have
not been updated are also taken from these two additional sources. We compare
our calculated fractional ionic abundances using these data with those
presented by Mazzotta et al. for all elements from H to Ni. The differences in
peak fractional abundance are up to 60%. We also compare with the fractional
ionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR
calculations of \citet{Gu03a,Gu04a} for the H-like through Na-like ions, and
the RR calculations of \citet{Gu03b} for the bare through F-like ions. These
results are in better agreement with our work, with differences in peak
fractional abundance of less than 10%. | astro-ph |
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