51 research outputs found
Inverting Color–Magnitude Diagrams to Access Precise Star Cluster Parameters: A New White Dwarf Age for the Hyades
We have extended our Bayesian modeling of stellar clusters—which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres—to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 ± 45 Myr, consistent with the best prior analysis of the cluster main-sequence turnoff (MSTO) age by Perryman et al. Since the faintest WDs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster\u27s WD age. Our result demonstrates the power of the bright WD technique for deriving ages and further demonstrates complete age consistency between WD cooling and MSTO ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr
SDSS J142625.71+575218.3: A Prototype for A New Class of Variable White Dwarf
We present the results of a search for pulsations in six of the recently discovered carbon-atmosphere white dwarf ("hot DQ") stars. On the basis of our theoretical calculations, the star SDSS J142625.71 + 575218.3 is the only object expected to pulsate. We observe this star to be variable, with significant power at 417.7 s and 208.8 s ( first harmonic), making it a strong candidate as the first member of a new class of pulsating white dwarf stars, the DQVs. Its folded pulse shape, however, is quite different from that of other white dwarf variables and shows similarities with that of the cataclysmic variable AM CVn, raising the possibility that this star may be a carbon-transferring analog of AM CVn stars. In either case, these observations represent the discovery of a new and exciting class of object.NSF AST-0507639, AST-0602288, AST-0607480, AST-0307321Astronom
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Limits On Planets Around Pulsating White Dwarf Stars
We present limits on planetary companions to pulsating white dwarf stars. A subset of these stars exhibit extreme stability in the period and phase of some of their pulsation modes; a planet can be detected around such a star by searching for periodic variations in the arrival time of these pulsations. We present limits on companions greater than a few Jupiter masses around a sample of 15 white dwarf stars as part of an ongoing survey. One star shows a variation in arrival time consistent with a 2M(J) planet in a 4.5 yr orbit. We discuss other possible explanations for the observed signal and conclude that a planet is the most plausible explanation based on the data available.NASA Origins NAG5-13094Astronom
The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs
We present a detailed analysis of the white dwarf luminosity functions
derived from the local 40 pc sample and the deep proper motion catalog of Munn
et al (2014, 2017). Many of the previous studies ignored the contribution of
thick disk white dwarfs to the Galactic disk luminosity function, which results
in an erronous age measurement. We demonstrate that the ratio of thick/thin
disk white dwarfs is roughly 20\% in the local sample. Simultaneously fitting
for both disk components, we derive ages of 6.8-7.0 Gyr for the thin disk and
8.7 0.1 Gyr for the thick disk from the local 40 pc sample. Similarly, we
derive ages of 7.4-8.2 Gyr for the thin disk and 9.5-9.9 Gyr for the thick disk
from the deep proper motion catalog, which shows no evidence of a deviation
from a constant star formation rate in the past 2.5 Gyr. We constrain the time
difference between the onset of star formation in the thin disk and the thick
disk to be Gyr. The faint end of the luminosity function
for the halo white dwarfs is less constrained, resulting in an age estimate of
Gyr for the Galactic inner halo. This is the first time
ages for all three major components of the Galaxy are obtained from a sample of
field white dwarfs that is large enough to contain significant numbers of disk
and halo objects. The resultant ages agree reasonably well with the age
estimates for the oldest open and globular clusters.Comment: ApJ, in pres
Statistical analysis of stellar evolution
Color-Magnitude Diagrams (CMDs) are plots that compare the magnitudes
(luminosities) of stars in different wavelengths of light (colors). High
nonlinear correlations among the mass, color, and surface temperature of newly
formed stars induce a long narrow curved point cloud in a CMD known as the main
sequence. Aging stars form new CMD groups of red giants and white dwarfs. The
physical processes that govern this evolution can be described with
mathematical models and explored using complex computer models. These
calculations are designed to predict the plotted magnitudes as a function of
parameters of scientific interest, such as stellar age, mass, and metallicity.
Here, we describe how we use the computer models as a component of a complex
likelihood function in a Bayesian analysis that requires sophisticated
computing, corrects for contamination of the data by field stars, accounts for
complications caused by unresolved binary-star systems, and aims to compare
competing physics-based computer models of stellar evolution.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS219 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Bayesian Inference for the White Dwarf Initial-Final Mass Relation
Stars lose mass as they age, and understanding mass loss is important for understanding stellar evolution. The initial-final mass relation (IFMR) is the relationship between a white dwarf’s initial mass on the main sequence and its final mass. We have developed a new method for fitting the IFMR based on a Bayesian analysis of photometric observations, combining deterministic models of stellar evolution in an internally coherent way. No mass data are used. Our method yields precise inferences (with uncertainties) for a parameterized linear IFMR. Our method can also return posterior distributions of white dwarf initial and final masses
Spitzer Planet Limits around the Pulsating White Dwarf GD66
We present infrared observations in search of a planet around the white
dwarf, GD66. Time-series photometry of GD66 shows a variation in the arrival
time of stellar pulsations consistent with the presence of a planet with mass >
2.4Mj. Any such planet is too close to the star to be resolved, but the
planet's light can be directly detected as an excess flux at 4.5um. We observed
GD66 with the two shorter wavelength channels of IRAC on Spitzer but did not
find strong evidence of a companion, placing an upper limit of 5--7Mj on the
mass of the companion, assuming an age of 1.2--1.7Gyr.Comment: 10 pages, accepted by Ap
White dwarf luminosity and mass functions from sloan digital sky survey spectra
We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g - i) and apparent magnitude (g) that covers the range -1.0 eff≲ 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with Teff< 12,000 K. Finally, we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
Bayesian Analysis for Stellar Evolution with Nine Parameters (BASE-9): User's Manual
BASE-9 is a Bayesian software suite that recovers star cluster and stellar
parameters from photometry. BASE-9 is useful for analyzing single-age,
single-metallicity star clusters, binaries, or single stars, and for simulating
such systems. BASE-9 uses Markov chain Monte Carlo and brute-force numerical
integration techniques to estimate the posterior probability distributions for
the age, metallicity, helium abundance, distance modulus, and line-of-sight
absorption for a cluster, and the mass, binary mass ratio, and cluster
membership probability for every stellar object. BASE-9 is provided as open
source code on a version-controlled web server. The executables are also
available as Amazon Elastic Compute Cloud images. This manual provides
potential users with an overview of BASE-9, including instructions for
installation and use.Comment: 22 pages, 7 figure
White dwarf luminosity and mass functions from sloan digital sky survey spectra
We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g - i) and apparent magnitude (g) that covers the range -1.0 eff≲ 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with Teff< 12,000 K. Finally, we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
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