scholarly journals An Example Demonstrating the Potential for Asteroseismology of DB White Dwarf Stars

1993 ◽  
Vol 139 ◽  
pp. 116-116
Author(s):  
P.A. Bradley ◽  
M.A. Wood
Keyword(s):  
Internal Structure ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Galactic Disk ◽  
Helium Surface ◽  
Dwarf Stars ◽  
University Of Texas ◽  
White Dwarf Stars ◽  
History Of

AbstractWe present the results of a parametric survey of evolutionary models of compositionally stratified white dwarfs with helium surface layers (DB white dwarfs). Because white dwarfs are the most common final end state of stellar evolution, determining their internal structure will offer us many clues about stellar evolution, the physics of matter under extreme conditions, plus the history of star formation and age of the local Galactic disk. As a first step towards determining the internal structure of DB white dwarf stars, we provide a comprehensive set of theoretical g-mode pulsation periods for comparison to observations.Because DB white dwarfs have a layered structure consisting of a helium layer overlying the carbon/oxygen core, some modes will have the same wavelength as the thickness of the helium layer, allowing a resonance to form. This resonance is called mode trapping (see Brassard et al. 1992 and references therein) and has directly observable consequences, because modes at or near the resonance have eigenfunctions and pulsation periods that are similar to each other. This results in much smaller period spacings between consecutive overtone modes of the same spherical harmonic index than the uniform period spacings seen between non-trapped modes. We demonstrate with an example how one can use the distribution of pulsation periods to determine the total stellar mass, the mass of the helium surface layer, and the extent of the helium/carbon and carbon/oxygen transition zones. With these tools, we have the prospect of being able to determine the structure of the observed DBV white dwarfs, once the requisite observations become available.We are grateful to C.J. Hansen, S.D. Kawaler, R.E. Nather, and D.E. Winget for their encouragement and many discussions. This research was supported by the National Science Foundation under grants 85-52457 and 90-14655 through the University of Texas and McDonald Observatory.

scholarly journals The Internal Structure of White Dwarf Stars Using the Whole Earth Telescope

1993 ◽  
Vol 139 ◽  
pp. 117-119
Author(s):  
P.A. Bradley
Keyword(s):  
Internal Structure ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
History Of ◽  
The Way ◽  
Whole Earth

AbstractWhite dwarfs are the final end state for the majority of stars, and hold clues to help solve many current pressing astrophysical problems. We can perform asteroseismology on the pulsating white dwarfs to better understand their internal structure and input physics, paving the way to a better understanding of astrophysics, stellar evolution, and the history of our Galaxy. I describe briefly the potential of asteroseismology by using it to infer the internal structure of PG1159-035.

scholarly journals Identification of Cool White Dwarfs in the Sloan Digital Sky Survey

2000 ◽  
Vol 176 ◽  
pp. 514-514 ◽  
Author(s):  
T. S. Metcalfe ◽  
A. Mukadam ◽  
D. E. Winget ◽  
X. Fan ◽  
M. A. Strauss ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Galactic Disk ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
History Of ◽  
Cool White Dwarfs

AbstractWe are searching for the coolest white dwarf stars in the galactic disk and halo. The Sloan survey, in due course, will identify an enormous number of new white dwarf stars which will better define the white dwarf luminosity function—an important tool for understanding the age and history of the stellar population of the galaxy. The broadband filter data obtained in the digital photometry phase of the survey will not permit identification of the most interesting of these, the coolest white dwarf stars. This is because the cool main sequence and subdwarf stars become indistinguishable from the white dwarfs in the various colorcolor diagrams. We have interference filters designed to separate out these classes of objects. We have obtained photometry of test fields to complement the Sloan data and identify the population of cool white dwarf stars. These data will ultimately resolve the controversies, based for the most part on small-number statistics, of the location of the turndown in the white dwarf luminosity function for the disk. If the halo is significantly older than the disk, we will find a second peak in the white dwarf luminosity function, at lower luminosities than the disk turndown. Our data will provide the first meaningful constraints on the location of the turndown in the halo white dwarf luminosity function.

scholarly journals Pulsations of White Dwarf Stars with Thick Hydrogen or Helium Surface Layers

1988 ◽  
Vol 123 ◽  
pp. 333-337
Author(s):  
Arthur N. Cox ◽  
Sumner G. Starrfield ◽  
Russell B. Kidman ◽  
W. Dean Pesnell
Keyword(s):  
Stellar Evolution ◽  
White Dwarf ◽  
Convection Zone ◽  
Helium Surface ◽  
Surface Layers ◽  
Dwarf Stars ◽  
Surface Mass ◽  
White Dwarf Stars ◽  
Surface Convection ◽  
Nonradial Pulsation

In order to see if there could be agreement between results of stellar evolution theory and those of nonradial pulsation theory, calculations of white dwarf models have been made for hydrogen surface masses of 10−4M⊙. Earlier results by Winget et al. (1982) indicated that surface masses greater than 10−8M⊙ would not allow nonradial pulsations, even though all the driving and damping is in surface layers only 10−12 of the mass thick. We show that the surface mass of hydrogen in the pulsating white dwarfs (ZZ Ceti variables) can be any value as long as it is thick enough to contain the surface convection zone.

scholarly journals Forever young white dwarfs: when stellar ageing stops

2020 ◽  
Author(s):  
Maria Camisassa ◽  
Leandro Althaus ◽  
Santiago Torres ◽  
Alejandro Córsico ◽  
Sihao Cheng ◽  
...  
Keyword(s):  
Energy Source ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Space Mission ◽  
Dwarf Stars ◽  
End Point ◽  
White Dwarf Stars ◽  
Single Standard ◽  
Stellar Mergers

Abstract White dwarf stars are the most common end point of stellar evolution. In particular, ultra-massive white dwarfs are expected to harbour oxygen-neon (ONe) cores as a result of single standard stellar evolution. However, a fraction of them could have carbon-oxygen (CO) cores and be born as a result of merger events. Recent observations provided by Gaia space mission, indicate that a fraction of the ultra-massive white dwarfs experience a strong delay in their cooling, which cannot be attributed only to the occurrence of crystallization, thus requiring an unknown energy source able to prolong their life for long periods of time. Here, we show that the energy released by 22Ne sedimentation in ultra-massive white dwarfs with CO cores is at the root of the long cooling delay of these stars. Our results provide solid sustain to the existence of CO-core ultra-massive white dwarfs and the occurrence of stellar mergers.

WHITE DWARFS AS LABORATORIES

2004 ◽  
Vol 13 (07) ◽  
pp. 1493-1508 ◽  
Author(s):  
S. O. KEPLER
Keyword(s):  
Internal Structure ◽  
White Dwarf ◽  
White Dwarfs ◽  
High Surface ◽  
High Density ◽  
Dwarf Stars ◽  
White Dwarf Stars

As 98% of all stars evolve into white dwarf starsm their study tell us about the evolution of the majority of stars. White dwarf stars show luminosity variations when their temperature reach instabilitity strips caused by high surface opacity. These variations are due to global pulsations that can be used to study the internal structure and evolution of the stars. Their observations can be used as laboratories to test physical theories at high density and temperature.

scholarly journals White Dwarf Stars

2017 ◽  
Vol 45 ◽  
pp. 1760023
Author(s):  
S. O. Kepler ◽  
Alejandra Daniela Romero ◽  
Ingrid Pelisoli ◽  
Gustavo Ourique
Keyword(s):  
White Dwarf ◽  
Final Stage ◽  
White Dwarfs ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
Multiple Systems ◽  
White Dwarf Stars ◽  
Sky Survey ◽  
Data Release ◽  
Low Mass

White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5[Formula: see text]000 to 39[Formula: see text]000. This number includes only white dwarf stars with [Formula: see text], i.e., excluding the Extremely Low Mass white dwarfs, which are necessarily the byproduct of stellar interaction.

scholarly journals Pulsations of White Dwarf Stars with Thick Hydrogen or Helium Surface Layers

1988 ◽  
pp. 333-337
Author(s):  
Arthur N. Cox ◽  
Sumner G. Starrfield ◽  
Russell B. Kidman ◽  
W. Dean Pesnell
Keyword(s):  
White Dwarf ◽  
Helium Surface ◽  
Surface Layers ◽  
Dwarf Stars ◽  
White Dwarf Stars

scholarly journals Pulsations of white dwarf stars with thick hydrogen or helium surface layers

1987 ◽  
Vol 317 ◽  
pp. 303 ◽  
Author(s):  
Arthur N. Cox ◽  
Russell B. Kidman ◽  
Sumner G. Starrfield ◽  
W. Dean Pesnell
Keyword(s):  
White Dwarf ◽  
Helium Surface ◽  
Surface Layers ◽  
Dwarf Stars ◽  
White Dwarf Stars

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 Asteroseismological Probing of the Thermal Evolution of White Dwarf Stars

1992 ◽  
Vol 9 ◽  
pp. 643-645
Author(s):  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Thermal Evolution ◽  
Sequence Evolution ◽  
Helium Burning ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
Low Mass

AbstractIt is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of helium burning, mostly carbon and oxygen. The exact proportions of C and 0 are unknown because of uncertainties in the nuclear rates of helium burning.

Sign in / Sign up

Export Citation Format

Share Document