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...
Constraining the Surface Inhomogeneity and Settling Times of Metals on Accreting White Dwarfs (2008)
Montgomery, M. H., Thompson, S. E., Von Hippel, T.
Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may...
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...
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...
Service Astrophysique Dapnia, M. Breger, M. H. Montgomery, S. Turcotte
. The effect of diffusion on the pulsations of main-sequence A and F stars is reviewed with a particular attention to Am, fl Doradus and Bootis stars. The discussion is made in the light of new...
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...
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...
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...
A New Technique for Probing Convection in Pulsating White Dwarf Stars (2005)
In this paper we demonstrate how pulsating white dwarfs can be used as an astrophysical laboratory for empirically constraining convection in these stars. We do this using a technique for fitting...
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...
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
In this paper we show how the formalism of Wu & Goldreich developed for weakly nonlinear white dwarf pulsations can be extended to the fully nonlinear case. Due to the computational simplification...
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 Crystal Method: Asteroseismology of BPM 37093 (2004)
Metcalfe, T. S., Montgomery, M. H., Kanaan, A.
More than 40 years have passed since Ed Salpeter and others predicted that the carbon/oxygen cores of the coolest white dwarf stars in our Galaxy will theoretically crystallize. This effect has a...
Corsico, A. H., Althaus, L. G., Montgomery, M. H., Garcia-Berro, E., Isern, J.
We present in this work new pulsational calculations for improved carbon-oxygen DA white dwarf models suitable for the study of massive ZZ Ceti stars. The background models employed in this study,...
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...
Metcalfe, T. S., Montgomery, M. H., Kanaan, A.
It was predicted more than 40 years ago that the cores of the coolest white dwarf stars should eventually crystallize. This effect is one of the largest sources of uncertainty in white dwarf cooling...
White dwarf envelopes: further results of a non-local model of convection (2004)
We present results of a fully non-local model of convection for white dwarf envelopes. We show that this model is able to reproduce the results of numerical simulations for convective efficiencies...
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...
Probing the core and envelope structure of DBV white dwarfs (2003)
Metcalfe, T. S., Montgomery, M. H., Kawaler, S. D.
We investigate the global pulsation properties of DBV white dwarf models that include both the double-layered envelope structure expected from time-dependent diffusion calculations, as well as a...
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...
Althaus, L. G., Serenelli, A. M., Corsico, A. H., Montgomery, M. H.
We present new and improved evolutionary calculations for carbon-oxygen white dwarf (WD) stars appropriate for the study of massive ZZ Ceti stars. We follow the complete evolution of massive WD...
The unusual pulsation spectrum of the cool ZZ Ceti star HS 0507+0434B (2002)
Handler, G., Romero-Colmenero, E., Montgomery, M. H.
We present the analysis of one week of single-site high-speed CCD photometric observations of the cool ZZ Ceti star HS 0507+0434B. Ten independent frequencies are detected in the star's light...
A-star envelopes: a test of local and non-local models of convection (2001)
We present results of a fully non-local, compressible model of convection for A-star envelopes. This model quite naturally reproduces a variety of results from observations and numerical simulations...
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...
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...