The Chemical Composition of White Dwarfs as a Test of Convective Efficiency during Core Helium Burning

2003 ◽  
Vol 583 (2) ◽  
pp. 878-884 ◽  
Author(s):  
Oscar Straniero ◽  
Inmaculada Dominguez ◽  
Gianluca Imbriani ◽  
Luciano Piersanti
Keyword(s):  
Chemical Composition ◽  
White Dwarfs ◽  
Helium Burning

scholarly journals 19. Convection Zones and Coronae of White Dwarfs

1971 ◽  
Vol 42 ◽  
pp. 130-135 ◽  
Author(s):  
K. H. Böhm ◽  
J. Cassinelli
Keyword(s):  
Chemical Composition ◽  
Temperature Gradient ◽  
White Dwarf ◽  
White Dwarfs ◽  
Convection Zone ◽  
Adiabatic Temperature ◽  
Turbulent Convection ◽  
Cool White Dwarfs ◽  
Adiabatic Temperature Gradient

Outer convection zones of white dwarfs in the range 5800 K ≤ Teff ≤ 30000 K have been studied assuming that they have the same chemical composition as determined by Weidemann (1960) for van Maanen 2. Convection is important in all these stars. In white dwarfs Teff < 8000 K the adiabatic temperature gradient is strongly influenced by the pressure ionization of H, HeI and HeII which occurs within the convection zone. Partial degeneracy is also important.Convective velocities are very small for cool white dwarfs but they reach considerable values for hotter objects. For a white dwarf of Teff = 30000 K a velocity of 6.05 km/sec and an acoustic flux (generated by the turbulent convection) of 1.5 × 1011 erg cm−2 sec−1 is reached. The formation of white dwarf coronae is briefly discussed.

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.

scholarly journals The chemical structure of the hot pulsating DB white dwarf KIC 08626021 from asteroseismology

2019 ◽  
Vol 15 (S357) ◽  
pp. 119-122
Author(s):  
S. Charpinet ◽  
P. Brassard ◽  
N. Giammichele ◽  
Gilles Fontaine
Keyword(s):  
Chemical Composition ◽  
White Dwarf ◽  
White Dwarfs ◽  
Chemical Structure ◽  
Neutrino Emission ◽  
Energy Losses ◽  
Seismic Model ◽  
Limited Impact ◽  
Static Models

AbstractGiammichele et al. (2018) proposed a full determination, largely independent of evolution calculations, of the chemical composition and stratification inside the hot pulsating DB white dwarf KIC 08626021. However, Timmes et al. (2018) pointed out that neglecting the effects of neutrino cooling, such as in the static models used in Giammichele et al. study, could impact significantly the derived seismic solution and compromise conclusions drawn upon it. Here we present a reanalysis of KIC 08626021, using improved static models which now incorporate more realistic luminosity profiles that reflect the still significant energy losses induced by neutrino emission mechanisms in hot DB white dwarfs. We show that this effect has only a limited impact on the derived seismic model properties and, more importantly, that all the conclusions brought by Giammichele et al. (2018) remain entirely valid.

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 Model Planetaries with rapidly evolving central stars: A case for FG Sge

1997 ◽  
Vol 180 ◽  
pp. 391-391
Author(s):  
K. Kifonidis ◽  
D. Schönberner
Keyword(s):  
White Dwarfs ◽  
Central Star ◽  
Frequency Of Occurrence ◽  
Helium Burning ◽  
Temporary Growth ◽  
Red Giant ◽  
Born Again ◽  
Thermal Pulses ◽  
Central Stars

Ever since the pioneering work of Schönberner (1979, A&A, 79, 108) and Iben (1984, ApJ, 277, 333) who showed that the evolution of post-AGB remnants might be affected by late thermal pulses of the helium-burning shell, resulting in a temporary growth of these objects to red giant dimensions, many attempts were made to explain a number of puzzling objects, among them the well-known variable central star FG Sge as well as the R CrB and PG 1159 stars, by this so-called “born-again AGB” scenario (Iben et al. 1983, ApJ, 264, 605; Iben & MacDonald 1995, in: White Dwarfs, Springer, p. 48). However, it is still not clear if the frequency of occurrence of such events is high enough as to be consistent with the number of born-again candidates. This is due to the very short evolutionary timescales during the pulse and the character of the post-pulse evolution which resembles the first post-AGB phase and makes it difficult for an observer to distinguish such objects from “normal” central stars.

scholarly journals Effects of rotation on the helium burning shell source in accreting white dwarfs

2004 ◽  
Vol 425 (1) ◽  
pp. 217-228 ◽  
Author(s):  
S.-C. Yoon ◽  
N. Langer ◽  
S. Scheithauer
Keyword(s):  
White Dwarfs ◽  
Helium Burning ◽  
Effects Of Rotation

scholarly journals Chemical Composition and Distribution of White Dwarfs

1968 ◽  
Vol 34 ◽  
pp. 423-424 ◽  
Author(s):  
Volker Weidemann
Keyword(s):  
Chemical Composition ◽  
Planetary Nebula ◽  
White Dwarfs

This contribution makes a few points which are relevant to the question of the fraction of white dwarfs formed via the planetary-nebula phenomenon.

scholarly journals Orbital Parameters and Chemical Composition of Four White Dwarfs in Post–Common‐Envelope Binaries

2008 ◽  
Vol 675 (2) ◽  
pp. 1518-1530 ◽  
Author(s):  
Adela Kawka ◽  
Stéphane Vennes ◽  
Jean Dupuis ◽  
Pierre Chayer ◽  
Thierry Lanz
Keyword(s):  
Chemical Composition ◽  
White Dwarfs ◽  
Orbital Parameters ◽  
Common Envelope
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