A5054816269- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- High-pressure geophysics and materials
- Astro and Planetary Science
- Fluid Dynamics Simulations and Interactions
- Computational Physics and Python Applications
- Superconducting Materials and Applications
- Particle Accelerators and Free-Electron Lasers
- Pulsars and Gravitational Waves Research
- Adaptive optics and wavefront sensing
- History and Developments in Astronomy
- Soil and Water Nutrient Dynamics
- Magnetic confinement fusion research
- Lattice Boltzmann Simulation Studies
- Fluid Dynamics and Heat Transfer
- Dark Matter and Cosmic Phenomena
- Scientific Research and Discoveries
- High-Velocity Impact and Material Behavior
- Particle accelerators and beam dynamics
- Spectroscopy and Laser Applications
- Marine and fisheries research
Texas A&M University – Commerce
2013-2024
Oregon Health & Science University
2024
Florida Institute of Technology
2003-2013
University of New Hampshire at Manchester
2011
Radboud University Nijmegen
2009
The University of Texas at Austin
1987-2008
Monterey Institute for Research in Astronomy
1998
University of Hawaiʻi at Mānoa
1994-1995
National Institute of Standards and Technology
1994
Université de Montréal
1991
Using WFPC2 on the Hubble Space Telescope, we have isolated a sample of 258 white dwarfs (WDs) in Galactic globular cluster M4. Fields at three radial distances from center were observed, and sizable WD populations found all three. The location these WDs color-magnitude diagram, their mean mass 0.51(±0.03) M☉, luminosity function confirm basic tenets stellar evolution theory support results current cooling theory. are used to extend main-sequence upward stars that already completed nuclear...
The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations pulsating dwarfs, we can measure their internal structures compositions, critical to understanding post main sequence evolution, along with cooling rates, allowing us calibrate ages directly. most important set dwarf variables oldest pulsators, cool DAVs, which have not previously been explored through asteroseismology due complexity instability. a time-series photometry...
We describe the remote facilities operated by Southeastern Association for Research in Astronomy (SARA), a consortium of colleges and universities US partnered with Lowell Observatory, Chilean National Telescope Allocation Committee, Instituto de Astrofisica Canarias. SARA observatories comprise 0.96m telescope at Kitt Peak, Arizona; 0.6m instrument on Cerro Tololo, Chile; 1m Jacobus Kapteyn Roque los Muchachos, La Palma, Spain. All are using standard VNC or Radmin protocols communicating...
We present the results of a three-continent multisite photometric campaign carried out on Algol-type eclipsing binary system Y Cam, in which primary component is multiperiodic δ Sct-type pulsator. The observations consist 86 nights and more than 450 h useful data collected mainly during Northern winter 2002–2003. This means that this most extensive time series for such kind systems obtained so far. These were mostly Johnson V filter, but they also include, first time, nearly complete light...
We report on the analysis of Kepler short-cadence (SC) light curve V344 Lyr obtained during 2009 June 20 through 2010 Mar 19 (Q2--Q4). The system is an SU UMa star showing dwarf nova outbursts and superoutbursts, promises to be a touchstone for CV studies foreseeable future. displays both positive negative superhumps with periods 2.20 2.06-hr, respectively, we identify orbital period 2.11-hr. have maximum amplitude ~0.25-mag, ~0.8 mag, at quiescence has ~0.025 mag. quality data such that can...
Context. Ultracompact X-ray binaries (UCXBs) typically consist of a white dwarf donor and neutron star or black hole accretor. The evolution UCXBs very low mass ratio in general is poorly understood. Aims. We investigate the order to learn for which ratios accretor types these systems can exist, if they do, what are their orbital spin periods, transfer rates evolutionary timescales. Methods. For different assumptions concerning accretion disk behavior we calculate system parameters dynamical...
We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The distribution we derive for 41 DA dwarfs this study has a mean 0.68 ± 0.04 M⊙. This slightly higher larger dispersion than most previous studies. hypothesize that is due to fraction cool (average Teff ∼ 10,000 K), hence old, our sample. Our results indicate samples made up predominantly cool, old tend have bimodal with second peak at...
view Abstract Citations (95) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Detection of the Evolutionary Time Scale DA White Dwarf G117-B15A with Whole Earth Telescope Kepler, S. O. ; Winget, D. E. Nather, R. Bradley, P. A. Grauer, Fontaine, G. Bergeron, Vauclair, Claver, C. F. Marar, T. M. K. Seetha, Ashoka, B. N. Mazeh, Leibowitz, Dolez, Chevreton, Barstow, Clemens, J. Kleinman, Sansom, Tweedy, W. Kanaan, Hine, Provencal, L. Wesemael,...
It has been suspected for over 20 years that the observed negative superhumps in cataclysmic variables are due to retrograde precession of a tilted disk. We present new smooth particle hydrodynamics simulation results demonstrate source modulation luminosity light negatively superhumping variable is transit bright spot across face an accretion disk out orbital plane. In untilted always located on outer edge disk, and intrinsic brightness constant at equilibrium. However, if plane only slowly...
Negative superhumps in cataclysmic variable systems result when the accretion disc is tilted with respect to orbital plane. The line of nodes precesses slowly retrograde direction, resulting a photometric signal period slightly less than period. We use method smoothed particle hydrodynamics simulate series models differing mass ratio and effective viscosity determine precession superhump deficit $\varepsilon_-$ as function system $q$. tabulate our results present fits both $\varepsilon_+$...
We present time-dependent modeling based on the accretion disk limit cycle model for a 270 d light curve of short-period SU UMa-type dwarf nova V344 Lyr taken by Kepler. The unprecedented precision and cadence (1 minute) far surpass that generally available long-term curves. data encompass two superoutbursts 17 normal (i.e., short) outbursts. main decay is nearly perfectly exponential, decaying at rate ∼12 mag−1, while much more rapid decays outbursts exhibit faster-than-exponential shape....
We examine the Kepler light curves of V1504 Cyg and V344 Lyr, encompassing ~736 d at 1 min cadence. During this span each system exhibited ~64-65 outbursts, including six superoutbursts. find that, in both systems, normal outbursts between two superoutbursts increase duration over time by a factor ~1.2-1.9, then reset to small value after following superoutburst. In systems trend quiescent intervals is local maximum about half way through supercycle - interval from one superoutburst next...
We report on analysis of 308.3 hrs high speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with Whole Earth Telescope (WET) during 2008 international observing run XCOV26. Fourier transform light curve contains 19 independent frequencies and numerous combination frequencies. dominant peaks are 1633.907, 1887.404, 2504.897 microHz. Our amplitudes reveals that parent consistent modes spherical degree l=1. also provide m identifications for largest...
We report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high‐excitation spectra, complex line profiles signifying mass loss at particular orbital phases, similar periods (respectively, 0.12433 0.12056 days). They are well‐credentialed members SW Sex class cataclysmic variables. Their light curves also quite complex. Oph shows periodic signals with 0.12090(8) 4.37(15) days, J1643.7+3402 0.11696(8) 4.05(12) days....
The timing capabilities and sensitivity of Kepler, NASA's observatory to find Earth-sized planets within the habitable zone stars, are well matched timescales amplitudes accretion disk variability in cataclysmic variables. This instrumental combination provides an unprecedented opportunity test refine stellar paradigms with high-precision, uniform data, containing none diurnal or season gaps that limit ground-based observations. We present a 3-month, 1 minute cadence Kepler light curve V344...
In recent years, a handful of systems have been observed to show "negative" (nodal) superhumps, with periods slightly shorter than the orbital period. It has suggested that these modes are consequence slow retrograde precession line nodes in disk tilted respect plane. Our simulations confirm and refine this model: they suggest roughly axisymmetric, retrogradely precessing, is driven at period less half as tidal field orbiting secondary encounters, turn, two halves above below midplane. Each...
view Abstract Citations (71) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Whole Earth Telescope Observations and Seismological Analysis of the Pre--White Dwarf PG 2131+066 Kawaler, S. D. ; O'Brien, M. Clemens, J. C. Nather, R. E. Winget, Watson, T. K. Yanagida, Dixson, Bradley, P. A. Wood, Sullivan, Kleinman, Meistas, Leibowitz, Moskalik, Zola, Pajdosz, G. Krzesinski, Solheim, -E. Bruvold, O'Donoghue, Katz, Vauclair, Dolez, N. Chevreton,...
HR 1217 is a prototypical rapidly oscillating Ap star that has presented test to the theory of non-radial stellar pulsation. Prior observations showed clear pattern five modes with alternating frequency spacings 33.3 and 34.6 μHz, sixth mode at problematic spacing 50.0 μHz (which equals 1.5×33.3 μHz) high-frequency side. Asymptotic pulsation allowed for 34 but Hipparcos rule out such spacing. Theoretical calculations magnetoacoustic in stars by Cunha predicted there should be previously...
We present the results of an analysis data covering 1.5 years dwarf nova V447 Lyr. detect eclipses accretion disk by mass donating secondary star every 3.74 hrs which is binary orbital period. Lyr therefore first in Kepler field to show eclipses. also five long outbursts and six short showing a U Gem type nova. that phase mid-eclipse occurs earlier during compared quiescence width eclipse greater outburst. This suggests bright spot more prominent larger outburst than quiescence. consistent...
The energy production time series of our purely hydrodynamic accretion disk simulations display remarkable similarities with the observed light curves dwarf novae superhumps in general and AM CVn stars particular. superhump period excess as a function mass ratio agrees well earlier theoretical numerical results, amplitudes relative phases harmonics power spectra agree observations. morphology mean pulse profile appears to be useful predictor system ratio. Our modified smoothed particle...
This paper analyses the Whole Earth Telescope observations of HL Tau 76, first discovered pulsating DA white dwarf. The star was observed during two campaigns. It a second priority target XCOV13 campaign in 1996 and one XCOV18 1999. 1999 reached 66.5% duty cycle. With total duration 18 days, frequency resolution achieved is 0.68 μHz. such resolution, we were able to find as many 78 significant frequencies power spectrum, which 34 are independent after removal all linear combinations. In...
We report the discovery of partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair chromospherically active dM4 stars in circular 1.6 d orbit. Light velocity curve modeling to our differential photometry data show each star has mass radius 0.340+/-0.014 M_sun 0.33+/-0.02 R_sun. The itself part common proper motion 133-374 cool DC or possible DA white dwarf 0.49-0.82 M_sun, which would make system at...
Observationally, white dwarf stars are a remarkably homogeneous class with minimum observed Teff ~ 4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than which main-sequence evolutionary timescales. As result, luminosity function has for last decade been used as probe of age and star formation rate Galactic disk, providing an estimated local disk ~10 Gyr total uncertainties roughly 20%. A long-standing criticism technique reality...