1,546 research outputs found
KOI 1224, a Fourth Bloated Hot White Dwarf Companion Found With Kepler
We present an analysis and interpretation of the Kepler binary system KOI
1224. This is the fourth binary found with Kepler that consists of a thermally
bloated, hot white dwarf in a close orbit with a more or less normal star of
spectral class A or F. As we show, KOI 1224 contains a white dwarf with Teff =
14400 +/- 1100 K, mass = 0.20 +/- 0.02 Msun, and radius = 0.103 +/- 0.004 Rsun,
and an F-star companion of mass = 1.59 +/- 0.07 Msun that is somewhat beyond
its terminal-age main sequence. The orbital period is quite short at 2.69802
days. The ingredients that are used in the analysis are the Kepler binary light
curve, including the detection of the Doppler boosting effect; the NUV and FUV
fluxes from the Galex images of this object; an estimate of the spectral type
of the F-star companion; and evolutionary models of the companion designed to
match its effective temperature and mean density. The light curve is modelled
with a new code named Icarus which we describe in detail. Its features include
the full treatment of orbital phase-resolved spectroscopy, Doppler boosting,
irradiation effects and transits/eclipses, which are particularly suited to
irradiated eclipsing binaries. We interpret the KOI 1224 system in terms of its
likely evolutionary history. We infer that this type of system, containing a
bloated hot white dwarf, is the direct descendant of an Algol-type binary. In
spite of this basic understanding of the origin of KOI 1224, we discuss a
number of problems associated with producing this type of system with this
short of an short orbital period.Comment: 14 pages, 8 figures, 2 tables, submitted to Ap
First results from the IllustrisTNG simulations: the galaxy color bimodality
We introduce the first two simulations of the IllustrisTNG project, a next
generation of cosmological magnetohydrodynamical simulations, focusing on the
optical colors of galaxies. We explore TNG100, a rerun of the original
Illustris box, and TNG300, which includes 2x2500^3 resolution elements in a
volume twenty times larger. Here we present first results on the galaxy color
bimodality at low redshift. Accounting for the attenuation of stellar light by
dust, we compare the simulated (g-r) colors of 10^9 < M*/Msun < 10^12.5
galaxies to the observed distribution from the Sloan Digital Sky Survey (SDSS).
We find a striking improvement with respect to the original Illustris
simulation, as well as excellent quantitative agreement in comparison to the
observations, with a sharp transition in median color from blue to red at a
characteristic M* ~ 10^10.5 Msun. Investigating the build-up of the color-mass
plane and the formation of the red sequence, we demonstrate that the primary
driver of galaxy color transition in the TNG model is supermassive blackhole
feedback in its low-accretion state. Across the entire population we measure a
median color transition timescale dt_green of ~1.6 Gyr, a value which drops for
increasingly massive galaxies. We find signatures of the physical process of
quenching: at fixed stellar mass, redder galaxies have lower SFRs, gas
fractions, and gas metallicities; their stellar populations are also older and
their large-scale interstellar magnetic fields weaker than in bluer galaxies.
Finally, we measure the amount of stellar mass growth on the red sequence.
Galaxies with M* > 10^11 Msun which redden at z<1 accumulate on average ~25% of
their final z=0 mass post-reddening; at the same time, ~18% of such massive
galaxies acquire half or more of their final stellar mass while on the red
sequence.Comment: The IllustrisTNG project website is http://www.tng-project.or
Continuous-time histories: observables, probabilities, phase space structure and the classical limit
In this paper we elaborate on the structure of the continuous-time histories
description of quantum theory, which stems from the consistent histories
scheme. In particular, we examine the construction of history Hilbert space,
the identification of history observables and the form of the decoherence
functional (the object that contains the probability information). It is shown
how the latter is equivalent to the closed-time-path (CTP) generating
functional. We also study the phase space structure of the theory first through
the construction of general representations of the history group (the analogue
of the Weyl group) and the implementation of a histories Wigner-Weyl transform.
The latter enables us to write quantum theory solely in terms of phase space
quantities. These results enable the implementation of an algorithm for
identifying the classical (stochastic) limit of a general quantum system.Comment: 46 pages, latex; in this new version typographical errors have been
removed and the presentation has been made cleare
Continuous stellar mass-loss in N-body models of galaxies
We present an N-body computer code - aimed at studies of galactic dynamics -
with a CPU-efficient algorithm for a continuous (i.e. time-dependent) stellar
mass-loss. First, we summarize available data on stellar mass-loss and derive
the long-term (20 Gyr) dependence of mass-loss rate of a coeval stellar
population. We then implement it, through a simple parametric form, into a
particle-mesh code with stellar and gaseous particles. We perform several tests
of the algorithm reliability and show an illustrative application: a 2D
simulation of a disk galaxy, starting as purely stellar but evolving as
two-component due to gradual mass-loss from initial stars and due to star
formation. In a subsequent paper we will use the code to study what changes are
induced in galactic disks by the continuous gas recycling compared to the
instantaneous recycling approximation, especially the changes in star formation
rate and radial inflow of matter.Comment: accepted for publication in Astronomy & Astrophysics (13 pages, 11
postscript figures
The photometric properties of a vast stellar substructure in the outskirts of M33
We have surveyed sq.degrees surrounding M33 with CFHT MegaCam in the
g and i filters, as part of the Pan-Andromeda Archaeological Survey. Our
observations are deep enough to resolve the top 4mags of the red giant branch
population in this galaxy. We have previously shown that the disk of M33 is
surrounded by a large, irregular, low-surface brightness substructure. Here, we
quantify the stellar populations and structure of this feature using the PAndAS
data. We show that the stellar populations of this feature are consistent with
an old population with dex and an interquartile range in
metallicity of dex. We construct a surface brightness map of M33 that
traces this feature to mags\,arcsec. At these low surface
brightness levels, the structure extends to projected radii of kpc from
the center of M33 in both the north-west and south-east quadrants of the
galaxy. Overall, the structure has an "S-shaped" appearance that broadly aligns
with the orientation of the HI disk warp. We calculate a lower limit to the
integrated luminosity of the structure of mags, comparable to a
bright dwarf galaxy such as Fornax or AndII and slightly less than $1\$ of the
total luminosity of M33. Further, we show that there is tentative evidence for
a distortion in the distribution of young stars near the edge of the HI disk
that occurs at similar azimuth to the warp in HI. The data also hint at a
low-level, extended stellar component at larger radius that may be a M33 halo
component. We revisit studies of M33 and its stellar populations in light of
these new results, and we discuss possible formation scenarios for the vast
stellar structure. Our favored model is that of the tidal disruption of M33 in
its orbit around M31.Comment: Accepted for publication in ApJ. 17 figures. ApJ preprint forma
The photometric properties of a vast stellar substructure in the outskirts of M33
We have surveyed sq.degrees surrounding M33 with CFHT MegaCam in the
g and i filters, as part of the Pan-Andromeda Archaeological Survey. Our
observations are deep enough to resolve the top 4mags of the red giant branch
population in this galaxy. We have previously shown that the disk of M33 is
surrounded by a large, irregular, low-surface brightness substructure. Here, we
quantify the stellar populations and structure of this feature using the PAndAS
data. We show that the stellar populations of this feature are consistent with
an old population with dex and an interquartile range in
metallicity of dex. We construct a surface brightness map of M33 that
traces this feature to mags\,arcsec. At these low surface
brightness levels, the structure extends to projected radii of kpc from
the center of M33 in both the north-west and south-east quadrants of the
galaxy. Overall, the structure has an "S-shaped" appearance that broadly aligns
with the orientation of the HI disk warp. We calculate a lower limit to the
integrated luminosity of the structure of mags, comparable to a
bright dwarf galaxy such as Fornax or AndII and slightly less than $1\$ of the
total luminosity of M33. Further, we show that there is tentative evidence for
a distortion in the distribution of young stars near the edge of the HI disk
that occurs at similar azimuth to the warp in HI. The data also hint at a
low-level, extended stellar component at larger radius that may be a M33 halo
component. We revisit studies of M33 and its stellar populations in light of
these new results, and we discuss possible formation scenarios for the vast
stellar structure. Our favored model is that of the tidal disruption of M33 in
its orbit around M31.Comment: Accepted for publication in ApJ. 17 figures. ApJ preprint forma
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