scholarly journals White-dwarf asteroseismology: An update

2019 ◽  
Vol 15 (S357) ◽  
pp. 93-106
Author(s):  
Alejandro H. Córsico
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Theoretical Models ◽  
Space Mission ◽  
Stellar Rotation ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Current State ◽  
Deep Interior ◽  
The Universe

AbstractThe vast majority of stars that populate the Universe will end their evolution as white-dwarf stars. Applications of white dwarfs include cosmochronology, evolution of planetary systems, and also as laboratories to study non-standard physics and crystallization. In addition to the knowledge of their surface properties from spectroscopy combined with model atmospheres, the global pulsations that they exhibit during several phases of their evolution allow spying on the deep interior of these stars. Indeed, by means of asteroseismology, an approach based on the comparison between the observed pulsation periods of variable white dwarfs and the periods predicted by representative theoretical models, we can infer details of the internal chemical stratification, the total mass, and even the stellar rotation profile and strength of magnetic fields. In this article, we review the current state of the area, emphasizing the latest findings provided by space-mission data.

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.

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 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.

Results on (UN)Published Wet Runs on Pulsating DB White Dwarfs

2003 ◽  
Vol 12 (1) ◽  
Author(s):  
G. Handler
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Archival Data ◽  
Dwarf Stars ◽  
Preliminary Results ◽  
White Dwarf Stars ◽  
The Future

AbstractI have collected all the WET archival data on the pulsating DB white dwarf stars (DBVs) and re-reduced them. In addition, the WET has recently observed three DBVs. Preliminary results on PG 1115+158, PG 1351+489, KUV 05134+2605, PG 1654+160 and PG 1456+103 are presented, and the future use of the data is outlined.

scholarly journals The Distribution of Masses and Radii of White-Dwarf Stars

1978 ◽  
Vol 80 ◽  
pp. 117-120
Author(s):  
Harry L. Shipman
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Model Atmosphere ◽  
Selection Effects ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Status ◽  
The Mean

The status of determinations of white dwarf radii by model atmosphere methods is reviewed in this paper. Details will appear elsewhere (Shipman 1978). In brief, the results are that (i) the mean radius of a sample of 95 hydrogen-rich stars with parallaxes is 0.0131 R⊙; (ii) the mean radius of a sample of 13 helium-rich stars is 0.011 R⊙, indistinguishably different from the radius of the hydrogen-rich stars; and (iii) that the most serious limitation on our knowledge of the mean radius of white dwarfs is the influence of selection effects. An estimate of the selection effects indicates that the true mean white dwarf radius is near 0.011 R⊙.

scholarly journals Gaia Data Release 2 catalogue of extremely low-mass white dwarf candidates

2019 ◽  
Vol 488 (2) ◽  
pp. 2892-2903 ◽  
Author(s):  
Ingrid Pelisoli ◽  
Joris Vos
Keyword(s):  
White Dwarf ◽  
Theoretical Models ◽  
Dwarf Stars ◽  
Single Star ◽  
Common Envelope ◽  
White Dwarf Stars ◽  
Final Sample ◽  
Data Release ◽  
Low Mass ◽  
Binary Evolution

ABSTRACT Extremely low-mass white dwarf stars (ELMs) are M < 0.3 M⊙ helium-core white dwarfs born either as a result of a common-envelope phase or after a stable Roche lobe overflow episode in a multiple system. The Universe is not old enough for ELMs to have formed through single-star evolution channels. As remnants of binary evolution, ELMs can shed light onto the poorly understood phase of common-envelope evolution and provide constraints to the physics of mass accretion. Most known ELMs will merge in less than a Hubble time, providing an important contribution to the signal to be detected by upcoming space-based gravitational wave detectors. There are currently less than 150 known ELMs; most were selected by colour, focusing on hot objects, in a magnitude-limited survey of the Northern hemisphere only. Recent theoretical models have predicted a much larger space density for ELMs than estimated observationally based on this limited sample. In order to perform meaningful comparisons with theoretical models and test their predictions, a larger well-defined sample is required. In this work, we present a catalogue of ELM candidates selected from the second data release of Gaia (DR2). We have used predictions from theoretical models and analysed the properties of the known sample to map the space spanned by ELMs in the Gaia Hertzsprung–Russell diagram. Defining a set of colour cuts and quality flags, we have obtained a final sample of 5762 ELM candidates down to Teff ≈ 5000 K.

scholarly journals 11. Effective Temperatures of White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 67-76 ◽  
Author(s):  
J. B. Oke ◽  
H. L. Shipman
Keyword(s):  
Chemical Composition ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
Evolved Stars ◽  
White Dwarf Stars ◽  
Effective Temperatures ◽  
Highly Evolved

White dwarf stars are among the most challenging and interesting objects which can be studied. Because they represent the interiors of highly-evolved stars, the chemical composition can be enormously variable from object to object. Furthermore, because of the very large gravities, the composition of the atmosphere may be very different from that in the interior. The theory of the degenerate interior provides a relation among mass, radius and chemical composition. Since temperatures, effective gravities, and redshifts can, for certain stars, provide further relations between mass and radius, one can hope to make checks on the theory which are not possible with ordinary stars.

scholarly journals The High Resolution Spectrum of the Pulsating, Pre-White Dwarf Star PG 1159-035 (GW VIR)

1989 ◽  
Vol 114 ◽  
pp. 384-387
Author(s):  
James Liebert ◽  
F. Wesemael ◽  
D. Husfeld ◽  
R. Wehrse ◽  
S. G. Starrfield ◽  
...  
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
High Resolution Spectrum ◽  
Dwarf Star ◽  
Dwarf Stars ◽  
New Class ◽  
White Dwarf Stars ◽  
Nonradial Pulsation

First reported at the IAU Colloquium No. 53 on White Dwarfs (McGraw et al. 1979), PG 1159-035 (GW Vir) is the prototype of a new class of very hot, pulsating, pre-white dwarf stars. It shows complicated, nonradial pulsation modes which have been studied exhaustively, both observationally and theoretically. The effective temperature has been crudely estimated as 100,000 K with log g ~ 7 (Wesemael, Green and Liebert 1985, hereafter WGL).

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