The Physics of Crystallization from Globular Cluster White Dwarf Stars in NGC 6397 (2009)
Winget, D. E., Kepler, S. O., Campos, Fabiola, Montgomery, M. H., Girardi, Leo, Bergeron, P., ...
We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space...
2006 Whole Earth Telescope Observations of GD358: A New Look at the Prototype DBV (2008)
Provencal, J. L., Montgomery, M. H., Kanaan, A., Shipman, H. L., Childers, D., Baran, A., ...
We report on the analysis of 436.1 hrs of nearly continuous high-speed photometry on the pulsating DB white dwarf GD358 acquired with the Whole Earth Telescope (WET) during the 2006 international...
New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey (2008)
Nitta, A., Kleinman, S. J., Krzesinski, J., Kepler, S. O., Metcalfe, T. S., Mukadam, Anjum S., ...
We are searching for new He atmosphere white dwarf pulsators (DBVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter...
Pulsating White Dwarf Stars and Precision Asteroseismology (2008)
Galactic history is written in the white dwarf stars. Their surface properties hint at interiors composed of matter under extreme conditions. In the forty years since their discovery, pulsating white...
SDSS J142625.71+575218.3, a Prototype for a New Class of Variable White Dwarf (2008)
Montgomery, M. H., Williams, Kurtis A., Winget, D. E., Dufour, Patrick, Degennaro, Steven, Liebert, James
We present the results of a search for pulsations in six of the recently discovered carbon-atmosphere white dwarf ("hot DQ") stars. Based on our theoretical calculations, the star SDSS...
Metcalfe, T. S., O'Donoghue, D., Winget, D. E., Kilkenny, D., Van Wyk, F., ...
We present the analysis of a total of 177h of high-quality optical time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC 20058-5234. The bulk of the observations (135h) were...
Limits on Planets Around White Dwarf Stars (2008)
Mullally, F., Winget, D. E., Degennaro, Steven, Jeffery, Elizabeth, Thompson, S. E., Chandler, Dean
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...
The pulsation modes of the pre-white dwarf PG 1159-035 (2008)
Costa, J. E. S., Kepler, S. O., Winget, D. E., O'Brien, M. S., Kawaler, S. D., Costa, A. F. M., ...
Context. PG 1159-035, a pre-white dwarf with T_(eff) ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035...
The pulsation modes of the pre-white dwarf PG 1159-035 (2007)
Costa, J. E. S., Kepler, S. O., Winget, D. E., O'Brien, M. S., Kawaler, S. D., Costa, A. F. M., ...
PG 1159-035, a pre-white dwarf with T_eff=140,000 K, is the prototype of both two classes: the PG1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data...
Fine Grid Asteroseismology of R548 and G117-B15A (2007)
Bischoff-Kim, A., Montgomery, M. H., Winget, D. E.
We now have a good measurement of the cooling rate of G117-B15A. In the near future, we will have equally well determined cooling rates for other pulsating white dwarfs, including R548. The ability...
Strong limits on the DFSZ axion mass with G117-B15A (2007)
Bischoff-Kim, A., Montgomery, M. H., Winget, D. E.
We compute rates of period change (Pdots) for the 215s mode in G117-B15A and the 213s mode in R548, first for models without axions, and then for models with axions of increasing mass. We use the...
White Dwarf Luminosity and Mass Functions from Sloan Digital Sky Survey Spectra (2007)
DeGennaro, Steven, Von Hippel, Ted, Winget, D. E., Kepler, S. O., Nitta, Atsuko, Koester, Detlev, ...
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 for two or more different mass ranges. In this...
Mean ZZ Ceti pulsation period gauges stellar temperature (2006)
Mukadam, Anjum S., Montgomery, M. H., Kim, A., Winget, D. E., Kepler, S. O., Clemens, J. C.
The mean pulsation period of ZZ Ceti stars increases with decreasing effective temperature as we traverse from the blue to the red edge of the instability strip. This well-established correlation...
New Techniques to Determine Ages of Open Clusters Using White Dwarfs (2006)
Jeffery, E. J., Von Hippel, T., Jefferys, W. H., Winget, D. E., Stein, N., DeGennaro, S.
Currently there are two main techniques for independently determining the ages of stellar populations: main sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. Open...
A Spitzer White Dwarf Infrared Survey (2006)
Mullally, F., Kilic, Mukremin, Reach, William T., Kuchner, Marc J., Von Hippel, Ted, Burrows, Adam, ...
We present mid-infrared photometry of 124 white dwarf stars with Spitzer Space Telescope. Objects were observed simultaneously at 4.5 and 8.0um with sensitivities better than 1 mJy. This data can be...
Towards a pure ZZ Ceti instability strip (2006)
Castanheira, B. G., Kepler, S. O., Costa, A. F. M., Giovannini, O., Robinson, E. L., Winget, D. E., ...
We have observed again two stars inside the ZZ Ceti instability strip that were previously classified as not-observed-to-vary (NOV) by Mukadam et al. (2004) and found them to be low-amplitude...
Spitzer White Dwarf Planet Limits (2006)
Mullally, F., Von Hippel, Ted, Winget, D. E.
We present preliminary limits on the presence of planets around white dwarf stars using the IRAC photometer on the Spitzer space telescope. Planets emit strongly in the mid-infrared which allows...
Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst (2006)
Hynes, R. I., Robinson, E. L., Pearson, K. J., Gelino, D. M., Cui, W., Xue, Y., ...
We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray...
Debris Disks Around White Dwarfs: The DAZ Connection (2006)
Kilic, Mukremin, Von Hippel, Ted, Leggett, S. K., Winget, D. E.
We present near-infrared spectroscopic observations of 20 previously known DAZ white dwarfs obtained at the NASA Infrared Telescope Facility. Two of these white dwarfs (G29-38 and GD362) are known to...
Von Hippel, Ted, Jefferys, William H., Scott, James, Stein, Nathan, Winget, D. E., DeGennaro, Steven, ...
We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, metallicity, and...
The Mystery Deepens: Spitzer Observations of Cool White Dwarfs (2006)
Kilic, Mukremin, Von Hippel, Ted, Mullally, Fergal, Reach, William T., Kuchner, Marc J., Winget, D. E., ...
We present 4.5$\mu$m and 8$\mu$m photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with T_eff< 6000 K...
Further evidence for variable synchrotron emission in XTE J1118+480 in outburst (2006)
Hynes, R. I., Robinson, E. L., Pearson, K. J., Gelino, D. M., Cui, W., Xue, Y. Q., ...
We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray...
Discovery of eleven new ZZ Ceti stars. (2006)
Castanheira, B.G., Kepler, S.O., Mullally, F., Winget, D.E., Koester, D., Voss, B., ...
Discovery of eleven new ZZ Ceti stars (2005)
Castanheira, B. G., Kepler, S. O., Mullally, F., Winget, D. E., Koester, D., Voss, B., ...
We report the discovery of eleven new ZZ Cetis using telescopes at OPD (Observat\'orio do Pico dos Dias/LNA) in Brazil, the 4.1 m SOAR (Southern Astrophysical Research) telescope at Cerro Pachon,...
The Dust cloud around the White Dwarf G 29-38 (2005)
Reach, William T., Kuchner, Marc J., Von Hippel, Ted, Burrows, Adam, Mullally, Fergal, Kilic, Mukremin, ...
We present new observations of the white dwarf G 29-38 with the camera (4.5 and 8 microns), photometer (24 microns), and spectrograph (5.5-14 microns) of the Spitzer Space Telescope. This star has an...
The White Dwarf Luminosity Function from SDSS Imaging Data (2005)
Harris, Hugh C., Munn, Jeffrey A., Kilic, Mukremin, Liebert, James, Williams, Kurtis A., Von Hippel, Ted, ...
A sample of white dwarfs is selected from SDSS DR3 imaging data using their reduced proper motions, based on improved proper motions from SDSS plus USNO-B combined data. Numerous SDSS and followup...
Exploring uncharted territory in particles physics using pulsating white dwarfs: Prospects (2005)
Kim, Agnes, Winget, D. E., Montgomery, M. H.
Pulsating white dwarfs, especially DBVs, can be used as laboratories to study elusive particles such as plasmon neutrinos and axions. In the degenerate interiors of DBVs, plasmon decay is the...
Driving in ZZ Ceti stars - Problem solved? (2005)
Kim, A., Winget, D. E., Montgomery, M. H., Kepler, S. O.
There is a fairly tight correlation between the pulsation periods and effective temperatures of ZZ Ceti stars (cooler stars have longer periods). This seems to fit the theoretical picture, where...
Excess Infrared Radiation from a Massive DAZ White Dwarf: GD362 - a Debris Disk? (2005)
Kilic, Mukremin, Von Hippel, Ted, Leggett, S. K., Winget, D. E.
We report the discovery of excess K-band radiation from a massive DAZ white dwarf star, GD362. Combining infrared photometric and spectroscopic observations, we show that the excess radiation cannot...
Kilic, Mukremin, Mendez, R. A., Von Hippel, Ted, Winget, D. E.
We explore the nature of the faint blue objects in the Hubble Deep Field South. We have derived proper motions for the point sources in the Hubble Deep Field South using a 3 year baseline. Combining...
Measuring the evolution of the most stable optical clock G 117-B15A (2005)
Kepler, S. O., Costa, J. E. S., Castanheira, B. G., Winget, D. E., Mullally, Fergal, Nather, R. E., ...
We report our measurement of the rate of change of period with time dP/dt for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of...
Discovery of fourteen new ZZ Cetis with SOAR (2005)
Kepler, S. O., Castanheira, B. G., Saraiva, M. F. O., Nitta, A., Kleinman, S. J., Mullally, F., ...
We report the discovery of fourteen new ZZ Cetis with the 4.1m Southern Astrophysical Research telescope, at Cerro Pachon, in Chile. The candidates were selected from the SDSS (Sloan Digital Sky...
Ensemble Characteristics of the ZZ Ceti stars (2005)
Mukadam, Anjum S., Montgomery, M. H., Winget, D. E., Kepler, S. O., Clemens, J. C.
We present the observed pulsation spectra of all known non-interacting ZZ Ceti stars (hydrogen atmosphere white dwarf variables; DAVs) and examine changes in their pulsation properties across the...
Cool White Dwarfs in the Sloan Digital Sky Survey (2005)
Kilic, Mukremin, Munn, Jeffrey A., Harris, Hugh C., Liebert, James, Von Hippel, Ted, Williams, Kurtis A., ...
A reduced proper motion diagram utilizing Sloan Digital Sky Survey (SDSS) photometry and astrometry and USNO-B plate astrometry is used to separate cool white dwarf candidates from metal-weak,...
Eleven New DAVs from the Sloan Survey (2005)
Mullally, F., Thompson, S. E., Castanheira, B. G., Winget, D. E., Kepler, S. O., Eisenstein, D. J., ...
We report the discovery of eleven new variable DA white dwarf (ZZ Ceti) stars. Candidates were selected by deriving temperatures from model fits to spectra obtained from the Sloan Digital Sky Survey....
Kanaan, A., Nitta, A., Winget, D.E., Kepler, S.O., Montgomery, M.H., Metcalfe, T.S., ...
The definitive version of this paper is available from www.aanda.org
Kanaan, A., Nitta, A., Winget, D. E., Kepler, S. O., Montgomery, M. H., Metcalfe, T. S.
BPM 37093 is the only hydrogen-atmosphere white dwarf currently known which has sufficient mass (~ 1.1 M_sun) to theoretically crystallize while still inside the ZZ Ceti instability strip (T_eff ~...
The White Dwarf Luminosity Function: The Shape of Things to Come (2004)
Von Hippel, T., Kilic, M., Munn, J., Harris, H., Williams, K., Liebert, J., ...
We describe a new survey for cool white dwarfs that supplements Sloan Digital Sky Survey photometry with USNO proper motions and follow-up spectroscopy. To date we have discovered and...
White Dwarfs in Open Clusters: Calibrating the Clock (2004)
Von Hippel, T., Winget, D. E., Jefferys, W. H., Scott, J. G.
We present an update of our on-going effort to improve the precision of white dwarf cosmochronology via careful analyses of white dwarf photometry in open clusters. To improve the precision of white...
Photometric Identification of Cool White Dwarfs (2004)
Kilic, M., Winget, D. E., Von Hippel, Ted, Claver, C. F.
We investigate the use of a narrow-band DDO51 filter for photometric identification of cool white dwarfs. We report photometric observations of 30 known cool white dwarfs with temperatures ranging...
Re-defining the Empirical ZZ Ceti Instability Strip (2004)
Mukadam, Anjum S., Winget, D. E., Von Hippel, Ted, Montgomery, M. H., Kepler, S. O., Costa, A. F. M.
We use the new ZZ Ceti stars (hydrogen atmosphere white dwarf variables; DAVs) discovered within the Sloan Digital Sky Survey (Mukadam et al. 2004) to re-define the empirical ZZ Ceti instability...
Proper Motion Objects in the Hubble Deep Field (2004)
Kilic, M., Von Hippel, Ted, Mendez, R. A., Winget, D. E.
Using the deepest and finest resolution images of the Universe acquired with the Hubble Space Telescope and a similar image taken 7 years later for the Great Observatories Origins Deep Survey, we...
Winget, D. E., Sullivan, D. J., Metcalfe, T. S., Kawaler, S. D., Montgomery, M. H.
We demonstrate that plasmon neutrinos are the dominant form of energy loss in model white dwarf stars down to T_eff ~ 25,000 K, depending on the stellar mass. The lower end of this range overlaps the...
The core/envelope symmetry in pulsating stars (2003)
Montgomery, M. H., Metcalfe, T. S., Winget, D. E.
We demonstrate that there is an inherent symmetry in the way high-overtone stellar pulsations sample the core and the envelope, which can potentially lead to an ambiguity in the asteroseismologically...
The Everchanging Pulsating White Dwarf GD358 (2003)
Kepler, S. O., Nather, R. E., Winget, D. E., Nitta, A., Kleinman, S. J., Metcalfe, T., ...
We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired...
Identification of Cool White Dwarfs in the NOAO Deep Wide-Field Survey (2002)
Kilic, M., Winget, D. E., Von Hippel, T., Claver, C. F.
We report our search for the cool white dwarfs belonging to the Galactic disk by extending the NOAO Deep Wide-Field Survey. Narrow-band DDO51 photometry of the Deep Wide-Field Survey's northern field...
Search For Oxygen in Cool DQ White Dwarf Atmospheres (2002)
Kilic, M., Winget, D. E., Von Hippel, T., Lester, D. F., Saumon, D.
We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon...
Measuring ^{12}C(&alpha,&gamma)^{16}O from White Dwarf Asteroseismology (2002)
Metcalfe, T. S., Salaris, M., Winget, D. E.
During helium burning in the core of a red giant, the relative rates of the 3&alpha and ^{12}C(&alpha,&gamma)^{16}O reactions largely determine the final ratio of carbon to oxygen in the resulting...
Constraints on 12C(alpha,gamma)16O from White Dwarf Seismology (2001)
Metcalfe, T. S., Salaris, M., Winget, D. E.
For many years, astronomers have promised that the study of pulsating white dwarfs would ultimately lead to useful information about the physics of matter under extreme conditions of temperature and...
Preliminary Constraints on 12C(alpha,gamma)16O from White Dwarf Seismology (2001)
Metcalfe, T. S., Winget, D. E., Charbonneau, P.
For many years, astronomers have promised that the study of pulsating white dwarfs would ultimately lead to useful information about the physics of matter under extreme conditions of temperature and...
A New Very Cool White Dwarf Discovered by the Sloan Digital Sky Survey (2001)
Harris, H. C., Hansen, B. M. S., Liebert, J., Berk, D. E. Vanden, Anderson, S. F., Knapp, G. R., ...
Early data taken during commissioning of the SDSS have resulted in the discovery of a very cool white dwarf. It appears to have stronger collision induced absorption from molecular hydrogen than any...
The effect of 3-He diffusion on the pulsational spectra of DBV models (2000)
Montgomery, M. H., Metcalfe, T. S., Winget, D. E.
We consider envelopes of DB white dwarfs which are not composed of pure 4-He, but rather a mixture of 3-He and 4-He. Given this assumption, the same diffusive processes which produce a relatively...
Genetic-Algorithm-based Asteroseismological Analysis of the DBV White Dwarf GD 358 (2000)
Metcalfe, T. S., Nather, R. E., Winget, D. E.
White dwarf asteroseismology offers the opportunity to probe the structure and composition of stellar objects governed by relatively simple physical principles. The observational requirements of...
Evolutionary Timescale of the DAV G117-B15A: The Most Stable Optical Clock Known (2000)
Kepler, S. O., Mukadam, Anjum, Winget, D. E., Nather, R. E., Metcalfe, T. S., Reed, M. D., ...
We observe G117-B15A, the most precise optical clock known, to measure the rate of change of the main pulsation period of this blue-edge DAV white dwarf. Even though the obtained value is only within...
The Effect of Crystallization on the Pulsations of White Dwarf Stars (1999)
Montgomery, M. H., Winget, D. E.
We consider the pulsational properties of white dwarf star models with temperatures appropriate for the ZZ Ceti instability strip and with masses large enough that they should be substantially...
Evolutionary calculations of phase separation in crystallizing white dwarf stars (1999)
Montgomery, M. H., Klumpe, E. W., Winget, D. E., Wood, M. A.
We present an exploration of the significance of Carbon/Oxygen phase separation in white dwarf stars in the context of self-consistent evolutionary calculations. Because phase separation can...
Understanding the Cool DA White Dwarf, G29-38 (1997)
Kleinman, S. J., Nather, R. E., Winget, D. E., Clemens, J. C., Bradley, P. A., Kanaan, A., ...
The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and...