Althaus, L. G., Panei, J. A., Bertolami, M. M. Miller, García-Berro, E., Córsico, A. H., Romero, A. D., ...
We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB white dwarfs. White dwarf sequences are computed for a wide range...
Córsico, A. H., Althaus, L. G., Bertolami, M. M. Miller, Pérez, J. M. González, Kepler, S. O.
We present a pulsational stability analysis of hot post-AGB H-deficient pre-white dwarf stars with active He-burning shells. The stellar models employed are state-of-the-art equilibrium structures...
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...
Althaus, L. G., Panei, J. A., Miller Bertolami, M. M., García-Berro, E., Córsico, A. H., Romero, A. D., ...
SDSS White Dwarf mass distribution at low effective temperatures (2008)
Koester, D., Kepler, S. O., Kleinman, S. J., Nitta, A.
The DA white dwarfs in the Sloan Digital Sky Survey, as analyzed in the papers for Data Releases 1 and 4, show an increase in surface gravity towards lower effective temperatures below 11500 K. We...
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...
The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035 (2008)
Costa, J. E. S., Kepler, S. O.
PG 1159-035, a pre-white dwarf with T=140000 K, is the prototype of the PG1159 spectroscopic class and the DOV pulsating class. Changes in the star cause variations in its oscillation periods. The...
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...
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...
Evidence of thin helium envelopes in PG1159 stars (2008)
Althaus, L. G., Córsico, A. H., Bertolami, M. M. Miller, Kepler, S. O.
We present evidence that PG1159 stars could harbour He--rich envelopes substantially thinner than those predicted by current evolutionary models with current estimates of mass loss, which may 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...
Castanheira, B. G., Kepler, S. O.
We calculate and explore an extensive adiabatic model grid for pulsating white dwarfs with H dominated atmospheres, the ZZ Ceti stars. We also compared the computed modes with the observed ones for...
Asteroseismological measurements on PG 1159-035, the prototype of the GW Vir variable stars (2007)
Córsico, A. H., Althaus, L. G., Kepler, S. O., Costa, J. E. S., Bertolami, M. M. Miller
An asteroseismological study of PG 1159-035, the prototype of the GW Vir variable stars, has been performed on the basis of detailed and full PG1159 evolutionary models presented by Miller Bertolami...
The Hubbl, E Space, T El Escope, S. O. Kepler, E. L. Robinson, D. Koester, ...
We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV stars G226-29 and G185-32 and for the pulsating DBV star PG 1351]489 with the Hubble Space T elescope Faint Object...
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...
On the systematics of asteroseismological mass determinations of PG1159 stars (2007)
Althaus, L. G., Córsico, A. H., Kepler, S. O., Bertolami, M. M. Miller
We analyze systematics in the asteroseismological mass determination methods in pulsating PG 1159 stars. We compare the seismic masses resulting from the comparison of the observed mean period...
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...
White Dwarf Mass Distribution in the SDSS (2006)
Kepler, S. O., Kleinman, S. J., Nitta, A., Koester, D., Castanheira, B. G., Giovannini, O., ...
We determined masses for the 7167 DA and 507 DB white dwarf stars classified as single and non-magnetic in data release four of the Sloan Digital Sky Survey (SDSS). We obtained revised Teff and log g...
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...
Gemini spectra of 12000K white dwarf stars (2006)
Kepler, S. O., Castanheira, B. G., Costa, A. F. M., Koester, D.
We report signal-to-noise ratio SNR ~ 100 optical spectra for four DA white dwarf stars acquired with the GMOS spectrograph of the 8m Gemini north telescope. These stars have 18
Analysis of IUE spectra of helium-rich white dwarf stars (2006)
Castanheira, B. G., Kepler, S. O., Handler, G., Koester, D.
We studied the class of DB white dwarf stars, using re-calibrated UV spectra for thirty four DBs obtained with the IUE satellite. By comparing the observed energy distributions with model...
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 seven ZZ Ceti stars using a new photometric selection method. (2006)
Voss, B., Koester, D., Ostensen, R., Kepler, S.O., Napiwotzki, R., Homeier, D., ...
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,...
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...
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...
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 ~...
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...
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...
Mode identification of Pulsating White Dwarfs using the HST (2000)
Kepler, S. O., Robinson, E. L., Koester, D., Clemens, J. C., Nather, R. E., Jiang, X. J.
We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV stars G226-29 and G185-32, and for the pulsating DBV star PG1351+489 with the Hubble Space Telescope Faint Object...
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...
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...