scholarly journals EPIC 228782059: Asteroseismology of What Could Be the Coolest Pulsating Helium-atmosphere White Dwarf (DBV) Known

2021 ◽  
Vol 922 (1) ◽  
pp. 2
Author(s):  
R. M. Duan ◽  
W. Zong ◽  
J.-N. Fu ◽  
Y. H. Chen ◽  
J. J. Hermes ◽  
...  
Keyword(s):  
White Dwarf ◽  
Light Curves ◽  
Rotational Period ◽  
Optimal Model ◽  
Instability Strip ◽  
Dwarf Stars ◽  
Helium Atmosphere ◽  
White Dwarf Stars ◽  
Long Duration ◽  
Physical Treatments

Abstract We present analysis of a new pulsating helium-atmosphere (DB) white dwarf, EPIC 228782059, discovered from 55.1 days of K2 photometry. The long-duration, high-quality light curves reveal 11 independent dipole and quadruple modes, from which we derive a rotational period of 34.1 ± 0.4 hr for the star. An optimal model is obtained from a series of grids constructed using the White Dwarf Evolution Code, which returns M * = 0.685 ± 0.003M ⊙, T eff = 21,910 ± 23 K, and log g = 8.14 ± 0.01 dex. These values are comparable to those derived from spectroscopy by Koester & Kepler (20,860 ± 160 K, and 7.94 ± 0.03 dex). If these values are confirmed or better constrained by other independent works, it would make EPIC 228782059 one of the coolest pulsating DB white dwarf stars known, and would be helpful for testing different physical treatments of convection, and to further investigate the theoretical instability strip of DB white dwarf stars.

scholarly journals TESS first look at evolved compact pulsators

2019 ◽  
Vol 632 ◽  
pp. A42 ◽  
Author(s):  
Keaton J. Bell ◽  
Alejandro H. Córsico ◽  
Agnès Bischoff-Kim ◽  
Leandro G. Althaus ◽  
Paul A. Bradley ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Compact Objects ◽  
Stellar Structure ◽  
Evolutionary Stage ◽  
Pulsation Frequency ◽  
Instability Strip ◽  
Dwarf Stars ◽  
Helium Atmosphere ◽  
White Dwarf Stars

Context. Pulsation frequencies reveal the interior structures of white dwarf stars, shedding light on the properties of these compact objects that represent the final evolutionary stage of most stars. Two-minute cadence photometry from the Transiting Exoplanet Survey Satellite (TESS) records pulsation signatures from bright white dwarfs over the entire sky. Aims. As part of a series of first-light papers from TESS Asteroseismic Science Consortium Working Group 8, we aim to demonstrate the sensitivity of TESS data, by measuring pulsations of helium-atmosphere white dwarfs in the DBV instability strip, and what asteroseismic analysis of these measurements can reveal about their stellar structures. We present a case study of the pulsating DBV WD 0158−160 that was observed as TIC 257459955 with the two-minute cadence for 20.3 days in TESS Sector 3. Methods. We measured the frequencies of variability of TIC 257459955 with an iterative periodogram and prewhitening procedure. The measured frequencies were compared to calculations from two sets of white dwarf models to constrain the stellar parameters: the fully evolutionary models from LPCODE and the structural models from WDEC. Results. We detected and measured the frequencies of nine pulsation modes and eleven combination frequencies of WD 0158−160 to ∼0.01 μHz precision. Most, if not all, of the observed pulsations belong to an incomplete sequence of dipole (ℓ = 1) modes with a mean period spacing of 38.1 ± 1.0 s. The global best-fit seismic models from both LPCODE and WDEC have effective temperatures that are ≳3000 K hotter than archival spectroscopic values of 24 100–25 500 K; however, cooler secondary solutions are found that are consistent with both the spectroscopic effective temperature and distance constraints from Gaia astrometry. Conclusions. Our results demonstrate the value of the TESS data for DBV white dwarf asteroseismology. The extent of the short-cadence photometry enables reliably accurate and extremely precise pulsation frequency measurements. Similar subsets of both the LPCODE and WDEC models show good agreement with these measurements, supporting that the asteroseismic interpretation of DBV observations from TESS is not dominated by the set of models used. However, given the sensitivity of the observed set of pulsation modes to the stellar structure, external constraints from spectroscopy and/or astrometry are needed to identify the best seismic solutions.

scholarly journals Hot DQ white dwarfs: a pulsational test of the mixing scenario for their formation

2009 ◽  
Vol 5 (H15) ◽  
pp. 370-370
Author(s):  
A. Romero ◽  
A. H. Córsico ◽  
L. G. Althaus ◽  
E. García-Berro
Keyword(s):  
Stability Analysis ◽  
White Dwarf ◽  
White Dwarfs ◽  
Evolutionary Models ◽  
Instability Strip ◽  
Dwarf Stars ◽  
Photometric Variability ◽  
New Class ◽  
White Dwarf Stars ◽  
Born Again

Hot DQ white dwarfs constitute a new class of white dwarf stars, uncovered recently within the framework of SDSS project. There exist nine of them, out of a total of several thousands white dwarfs spectroscopically identified. Recently, three hot DQ white dwarfs have been reported to exhibit photometric variability with periods compatible with pulsation g-modes. In this contribution, we presented the results of a non-adiabatic pulsation analysis of the recently discovered carbon-rich hot DQ white dwarf stars. Our study relies on the full evolutionary models of hot DQ white dwarfs recently developed by Althaus et al. (2009), that consistently cover the whole evolution from the born-again stage to the white dwarf cooling track. Specifically, we performed a stability analysis on white dwarf models from stages before the blue edge of the DBV instability strip (Teff ≈ 30000 K) until the domain of the hot DQ white dwarfs (18000-24000 K), including the transition DB→hot DQ white dwarf. We explore evolutionary models with M*= 0.585M⊙ and M* = 0.87M⊙, and two values of thickness of the He-rich envelope (MHe = 2 × 10−7M* and MHe = 10−8M*).

scholarly journals Interacting Binary White Dwarf Stars

1992 ◽  
Vol 151 ◽  
pp. 461-464
Author(s):  
J.-E. Solheim
Keyword(s):  
White Dwarf ◽  
Structural Changes ◽  
Light Curves ◽  
Physical Parameters ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Test Models ◽  
Radial Pulsations ◽  
Whole Earth

This group of stars consists of 4 systems, also called helium cataclysmics. Three of them show photometric variations and have been studied by the Whole Earth Telescope (WET), which have revealed multiperiodic light curves showing the signature of g-mode non-radial pulsations on the accreting star. The combination of accretion and g-mode pulsations gives a unique opportunity to test models for the accreator's structural changes in response to accretion. IUE-spectra provide additional physical parameters.

scholarly journals Towards Ensemble Asteroseismology of the Pulsating DB White Dwarf Stars

2002 ◽  
Vol 185 ◽  
pp. 608-609
Author(s):  
G. Handler ◽  
M.A. Wood ◽  
A. Nitta ◽  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
The Other ◽  
Archival Data ◽  
Dwarf Stars ◽  
Helium Atmosphere ◽  
Individual Stars ◽  
White Dwarf Stars ◽  
Binary Evolution ◽  
Insight Into

The origin of the helium-atmosphere DB white dwarfs is still a matter of debate. In particular, the question is unresolved whether binary evolution produces a significant number of DBs. The pulsating DB white dwarfs (DBV stars) offer a complementary insight into this problem through asteroseismology; DBs descending from binaries will have different interior structures than DBs originating from single stars (Nitta & Winget, 1998).GD 358 is by far the best-observed pulsating DBV star, and the only one for which asteroseismology has been performed to date. This star’s structure has been shown to be inconsistent with an origin from binary evolution (Nitta & Winget, 1998), but most of the other DBVs are relatively poorly studied.We therefore analysed archival data on all DBVs and obtained new measurements of stars with very little data available (Table 1), firstly to identify suitable targets for asteroseismological investigations and secondly to examine the pulsation spectra of the DBVs as a group, following the works of Clemens (1994) and Kleinman (1995) on the pulsating DA white dwarfs. Our study also produced new seismological results on individual stars and promising targets for future Whole Earth Telescope (WET, Nather et al., 1990) runs.

scholarly journals Discovery of the sixth DBV Star: CBS 114

1989 ◽  
Vol 114 ◽  
pp. 290-292
Author(s):  
D. E. Winget ◽  
C. F. Claver
Keyword(s):  
White Dwarf ◽  
Compact Objects ◽  
Rich Source ◽  
Light Curves ◽  
Dwarf Stars ◽  
Temperature Variations ◽  
White Dwarf Stars

Though widely spread across the H-R diagram the compact pulsators have much in common. All are multi-periodic, and most have extremely complex light curves. All appear to be pulsating in nonradial g-modes, with temperature variations responsible for the bulk of the light modulations. The g-modes are global in nature and, typically, many are excited in each pulsator, so they are a rich source of seismological information about the interior regions of the white dwarf stars.The pulsating DB white dwarf stars (DBV’s) form one of the three distinct classes of pulsating compact objects currently known. We find these classes nearly uniformly distributed in log Te spanning virtually the whole range of the white dwarf cooling sequence, from the hot DOV stars at log Te ~ 5 to the DAV (ZZ Ceti) stars at log Te ~ 4; the DBV stars, with logTe ~ 4.5, fall in the middle.

scholarly journals Ground-based observation of ZZ Ceti stars and the discovery of four new variables

2019 ◽  
Vol 490 (2) ◽  
pp. 1803-1820 ◽  
Author(s):  
Alejandra D Romero ◽  
L Antunes Amaral ◽  
T Klippel ◽  
D Sanmartim ◽  
L Fraga ◽  
...  
Keyword(s):  
White Dwarf ◽  
Signal To Noise Ratio ◽  
Structural Parameters ◽  
Instability Strip ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Photometric Observations ◽  
Best Fitting ◽  
New Variables

ABSTRACT We perform ground-based photometric observations of 22 DA white dwarf stars, 10 already known ZZ Cetis and 12 candidates with atmospheric parameters inside the classical instability strip. We report on the discovery of four new variable DA white dwarf stars. Two objects are near the middle of the instability strip, SDSS J082804.63+094956.6 and SDSS J094929.09+101918.8, and two red edge pulsators, GD 195 and L495−82. In addition, we classified four objects as possible variables, since evidence of variability was detected in the light curve, but the signal-to-noise ratio was not sufficient to establish a definite detection. Follow-up observations were performed for 10 known ZZ Ceti stars to verify period stability and search for new periodicities. For each confirmed variable, we perform a detailed asteroseismological fit and compare the structural parameters obtained from the best-fitting models with those obtained from spectroscopy and photometry from Gaia. Finally we present a study of the asteroseismological properties of a sample of 91 ZZ Ceti stars.

scholarly journals Searching for ZZ Ceti white dwarfs in the Gaia survey

2019 ◽  
Vol 15 (S357) ◽  
pp. 123-126
Author(s):  
Olivier Vincent ◽  
Pierre Bergeron ◽  
David Lafrenière
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Physical Parameters ◽  
Hydrogen Line ◽  
Instability Strip ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Effective Temperatures

AbstractThe Gaia satellite recently released parallax measurements for nearly 400,000 white dwarf stars, allowing for precise measurements of their physical parameters. By combining these parallaxes with Pan-STARRS and CFIS-u photometry, we measured the effective temperatures and surface gravities for all white dwarfs within 100 pc and identified a sample of ZZ Ceti white dwarf candidates within the instability strip. We report the results of a photometric follow-up, currently under way, aimed at identifying new ZZ Ceti stars among this sample using the PESTO camera attached to the 1.6-m telescope at the Mont Mégantic Observatory. Our goal is to verify that ZZ Ceti stars occupy a region in the logg-Teff plane where no nonvariable stars are found, supporting the idea that ZZ Ceti pulsators represent a phase through which all hydrogen-line (DA) white dwarfs must evolve.

THE PULSATING WHITE DWARF G 185-32

2004 ◽  
Vol 13 (07) ◽  
pp. 1213-1216
Author(s):  
BÁRBARA GARCIA CASTANHEIRA ◽  
S. O. KEPLER
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Light Curves ◽  
Stellar Structure ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Non Linear ◽  
Linear Effects

We study the structure of pulsating white dwarf stars, which present multi-periodic light variations with periods around minutes, defining instability strips along their cooling sequence. We analyze the ultraviolet (HST) and optical (WET) light curves of the pulsating white dwarf G185-32. Among all pulsating white dwarfs, this star has the shortest periodicity so far observed. We detected 18 periodicities, including non-linear effects, which can be used to study the stellar structure, constraining the physics of the degenerate matter.

scholarly journals The Time Dependence of the Phases of the Harmonics Relative to the 1490 sec Fundamental in PG1346+082

1989 ◽  
Vol 114 ◽  
pp. 296-299
Author(s):  
J. L. Provencal ◽  
J. C. Clemens ◽  
G. Henry ◽  
B. P. Hine ◽  
R. E. Nather ◽  
...  
Keyword(s):  
White Dwarf ◽  
Compact Object ◽  
Detailed Knowledge ◽  
Line Profiles ◽  
Pressure Broadening ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Adequate Understanding ◽  
Magnitude Variation ◽  
Hydrogen Lines

White dwarf stars provide important boundary conditions for the understanding of stellar evolution. An adequate understanding of even these simple stars is impossible without detailed knowledge of their interiors. PG1346+082, an interacting binary white dwarf system, provides a unique opportunity to view the interior of one degenerate as it is brought to light in the accretion disk of the second star as the primary strips material from its less massive companion (see Wood et at. 1987).PG1346+082 is a photometric variable with a four magnitude variation over a four to five day quasi-period. A fast Fourier transform (FFT) of the light curve shows a complex, time-dependent structure of harmonics. PG1346+082 exhibits flickering – the signature of mass transfer. The optical spectra of the system contain weak emission features during minimum and broad absorption at all other times. This could be attributed to pressure broadening in the atmosphere of a compact object, or to a combination of pressure broadening and doppler broadening in a disk surrounding the compact accretor. No hydrogen lines are observed and the spectra are dominated by neutral helium. The spectra also display variable asymmetric line profiles.

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