A5070495906- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Pulsars and Gravitational Waves Research
- High-pressure geophysics and materials
- Optical Polarization and Ellipsometry
- History and Developments in Astronomy
- Atmospheric Ozone and Climate
- Spectroscopy and Laser Applications
- X-ray Diffraction in Crystallography
- Tactile and Sensory Interactions
- Superconducting and THz Device Technology
- CCD and CMOS Imaging Sensors
- Optical Coatings and Gratings
- Robotics and Sensor-Based Localization
- Spacecraft and Cryogenic Technologies
- Planetary Science and Exploration
- Tribology and Lubrication Engineering
- Astronomical and nuclear sciences
California Polytechnic State University
2017-2022
Brigham Young University
2003-2018
Carrier (United States)
2012-2014
James Madison University
2012-2014
Space Telescope Science Institute
2010-2011
University of Vermont
2010
University of California, Irvine
2010
Harvard University
2010
Siena College
2010
The University of Texas at Austin
2004-2010
During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, we have serendipitously discovered a new class low-amplitude, multimode sdB pulsators with periods order hour. These are more than factor 10 longer those previously known (EC 14026 stars), implying that they due gravity modes rather pressure modes. The period found only among cooler where surprisingly common. iron opacity instability drives short-period EC stars is...
We present a detailed analysis of the white dwarf luminosity functions derived from local 40 pc sample and deep proper motion catalog Munn et al (2014, 2017). Many previous studies ignored contribution thick disk dwarfs to Galactic function, which results in an erronous age measurement. demonstrate that ratio thick/thin is roughly 20\% sample. Simultaneously fitting for both components, we derive ages 6.8-7.0 Gyr thin 8.7 $\pm$ 0.1 Similarly, 7.4-8.2 9.5-9.9 catalog, shows no evidence...
We present limits on planetary companions to pulsating white dwarf stars. A subset of these stars exhibit extreme stability in the period and phase some their pulsation modes; a planet can be detected around such star by searching for periodic variations arrival time pulsations. greater than few Jupiter masses sample 15 as part an ongoing survey. One shows variation consistent with 2MJ 4.5 yr orbit. discuss other possible explanations observed signal conclude that is most plausible...
We present new UV-to-IR stellar photometry of four low-extinction windows in the Galactic bulge, obtained with Wide Field Camera 3 on Hubble Space Telescope (HST). Using our five bandpasses, we have defined reddening-free photometric indices sensitive to effective temperature and metallicity. find that bulge populations resemble those formed via classical dissipative collapse: each field is dominated by an old (∼10 Gyr) population exhibiting a wide metallicity range (−1.5≲ [Fe/H] ≲0.5)....
We have extended our Bayesian modeling of stellar clusters—which uses main-sequence evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling atmospheres—to include binary stars, field two additional models. As critical test technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions radial velocities, where available. Under the assumption particular set models atmosphere estimate age WDs be 648 ± 45 Myr, consistent best...
We use Hubble Space Telescope (HST) imaging from the ACS Treasury Survey to determine fits for single population isochrones of 69 Galactic globular clusters. Using robust Bayesian analysis techniques, we simultaneously ages, distances, absorptions, and helium values each cluster under scenario a "single" stellar on model grids with solar ratio heavy element abundances. The set parameters is determined in consistent reproducible manner all clusters using suite BASE-9. Our results are used...
We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main-sequence and white dwarf stars reveal the underlying cluster properties age, distance, metallicity, line-of-sight absorption, as well individual stellar masses. The advantages our has over traditional analyses are objectivity, precision, explicit dependence on prior knowledge parameters. Within confines given set often-used models evolution, single mapping initial final masses, cooling, assuming photometric...
We present deep photometric observations of the open cluster NGC 2477 using HST/WFPC2. By identifying seven white dwarf candidates, we an analysis age this cluster, both traditional method fitting isochrones to cooling sequence, and by employing a new Bayesian statistical technique that has been developed our group. This performs objective, simultaneous model fit stellar parameters (namely age, metallicity, distance, reddening, as well individual masses, mass ratios, membership) photometry....
A catalog of 8472 white dwarf (WD) candidates is presented, selected using reduced proper motions from the deep motion Munn et al. 2014. Candidates are in magnitude range 16 < r 21.5 over 980 square degrees, and 21.3 an additional 1276 within Sloan Digital Sky Survey (SDSS) imaging footprint. Distances, bolometric luminosities, atmospheric compositions derived by fitting SDSS ugriz photometry to pure hydrogen helium model atmospheres (assuming surface gravities log g = 8). The disk...
Abstract The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey of transiting planets orbiting bright stars for over 10 years. KELT images have pixel scale ∼23″ −1 —very similar to that NASA’s Transiting Exoplanet Survey Satellite ( TESS )—as well as large point-spread function, and the reduction pipeline uses weighted aperture with radius 3′. At this angular scale, multiple are typically blended in apertures. In order identify false positives...
We present HST/ACS observations of RR Lyrae variable stars in six ultra-deep fields the Andromeda galaxy (M31), including parts halo, disk, and giant stellar stream. Past work on M31 has focused various aspects populations that make up galaxy's their distances metallicities. This study builds upon this previous by increasing spatial coverage (something been lacking studies) searching for these constituents not yet explored. Besides 55 we found our initial field located 11 kpc from galactic...
The pulsating hydrogen atmosphere white dwarf star G 117-B15A has been observed since 1974. Its main pulsation period at 215.19738823(63) s, in optical light curves, varies by only (5.12+/-0.82)x10^{-15} s/s and shows no glitches, as pulsars do. rate of change corresponds to a the 1 s 6.2 million years. We demonstrate that this exceptional clock can continue put stringent limits on fundamental physics, such constraints interaction from hypothetical dark matter particles, well search for...
We report 490 radial velocities for 16 Galactic Cepheid variables. The typical uncertainty of a single velocity is ±0.40 km s-1. Comparison with published shows excellent agreement. Two the Cepheids (Z Lac, S Sge) are known binaries and exhibit orbital changes in our observing interval.
We report the discovery of three nearby old halo white dwarf (WD) candidates in Sloan Digital Sky Survey (SDSS), including two stars a common proper motion binary system. These are selected from our 2800deg2 survey on Bok and U.S. Naval Observatory Flagstaff Station 1.3 m telescopes, they display motions 04–05 yr−1. Follow-up MMT spectroscopy near-infrared photometry demonstrate that all objects hydrogen-dominated atmosphere WDs with Teff ≈ 3700–4100 K. For average mass WDs, these...
A new proper motion catalog is presented, combining the Sloan Digital Sky Survey (SDSS) with second epoch observations in r band within a portion of SDSS imaging footprint. The were obtained 90prime camera on Steward Observatory Bok 90 inch telescope, and Array Camera U.S. Naval Observatory, Flagstaff Station, 1.3 meter telescope. covers 1098 square degrees to = 22.0, an additional 1521 20.9, plus further 488 lesser quality data. Statistical errors motions range from 5 mas/year at bright end...
White dwarfs (WDs) offer unrealized potential in solving two problems astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures radii, which constrained with precision by high quality photometry parallaxes. Accurate precise Gaia parallaxes along photometric surveys provide information to derive total for vast numbers of WDs. Here we analyse 1372 WDs found wide binaries MS companions, report on the attainable these WD+MS systems. The a further...
Abstract Intricate computer models can be used to describe complex physical processes in astronomy such as the evolution of stars. Like a sampling distribution, these typically predict observed quantities function number unknown parameters. Including them components statistical model, however, leads significant modeling, inferential, and computational challenges. In this article, we tackle challenges study mass loss that stars experience they age. We have developed new Bayesian technique for...
A new class of pulsating subdwarf B stars has recently been announced by Green and coworkers. Here we present a follow-up paper describing our observations the pulsation structure prototype PG 1716+426. The oscillations are multiperiodic with periods between 0.8 1.4 hr (180-340 μHz) semiamplitudes less than 0.2%. We also observe that amplitudes appear variable, making 1716 complicated. an order magnitude longer those seen in EC 14026 (sdBV) stars, implying they gravity modes rather pressure...
In this paper, new Cousins VRI data are presented for NGC 752 and Praesepe, extant combined into an augmented database M67. For those three clusters, catalogs containing photometry, reddening-corrected values of (V − K)J, temperatures produced. The same is done Coma by using both previously published newly derived photometry. An set the Hyades updated to include V magnitudes (R I)C that were after original appeared. Finally, M67 Sandquist corrected effect depends on location face cluster....
Currently there are two main techniques for independently determining the ages of stellar populations: sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. Open clusters provide ideal environment calibration these clocks. Because current to derive from dwarfs observationally challenging, we discuss feasibility brighter alone. This would eliminate requirement observing coolest (i.e., faintest) dwarfs. We our method testing this new idea, as well required...
In this paper we apply a Bayesian technique to determine the best fit of stellar evolution models find main sequence turn off age and other cluster parameters four intermediate-age open clusters: NGC 2360, 2477, 2660, 3960. Our algorithm utilizes Markov chain Monte Carlo these various parameters, objectively finding best-fit isochrone for each cluster. The result is high-precision fit. We compare results with those traditional "by-eye" fitting methods. By applying 3960, ages clusters be 1.35...
We report 84 radial velocities for 36 field RR Lyrae variable stars. The typical uncertainty of a single velocity is estimated at ±0.5 km s-1. Our sample consists variables with insufficient pre-existing data reliable center-of-mass determinations. have computed from our new using Lyr templates. ±1.5 s-1 observed least three times.
The initial-final mass relation (IFMR) of white dwarfs (WDs) plays an important role in stellar evolution. To derive precise estimates IFMRs and explore how they may vary among star clusters, we propose a Bayesian hierarchical model that pools photo- metric data from multiple clusters. After performing simulation study to show the benefits model, apply this five clus- ters: Hyades, M67, NGC 188, 2168, 2477, leading reasonable consistent for these We illustrate cluster-specific analysis 188...
It takes years of effort employing the best telescopes and instruments to obtain high-quality stellar photometry, astrometry, spectroscopy. Stellar evolution models contain experience lifetimes theoretical calculations testing. Yet most astronomers fit these valuable precious datasets by eye. We show that a principled Bayesian approach fitting data yields substantially more information over range astrophysics. highlight advances in determining ages star clusters, mass ratios binary stars,...
We report the discovery of several optical burstlike events from low-mass X-ray binary MS 1603.6+2600 (UW CrB). The last for a few tens seconds, exhibit very fast rise and slow decay, involve brightening factor 2-3. flares appear distinct lower level flickering instead strongly resemble reprocessed type I bursts as seen in number other neutron star binaries. In conjunction with previously reported candidate burst, these confirm that compact object UW CrB is star. examine burst brightness...