Chemical stratification in white dwarf atmospheres and envelopes

2008 ◽  
pp. 206-219 ◽  
Author(s):  
D. Koester
Keyword(s):  
White Dwarf ◽  
Chemical Stratification

scholarly journals The potential of asteroseismology for probing the core chemical stratification in white dwarf stars

2017 ◽  
Vol 598 ◽  
pp. A109 ◽  
Author(s):  
N. Giammichele ◽  
S. Charpinet ◽  
P. Brassard ◽  
G. Fontaine
Keyword(s):  
White Dwarf ◽  
Dwarf Stars ◽  
The Core ◽  
White Dwarf Stars ◽  
Chemical Stratification

scholarly journals White Dwarf Seismology at the Université de Montréal

1993 ◽  
Vol 139 ◽  
pp. 120-120
Author(s):  
G. Fontaine ◽  
P. Brassard ◽  
P. Bergeron ◽  
F. Wesemael
Keyword(s):  
Specific Heat ◽  
Cooling Rate ◽  
Internal Structure ◽  
White Dwarf ◽  
White Dwarfs ◽  
Period Change ◽  
Core Material ◽  
The Core ◽  
Core Composition ◽  
Chemical Stratification

Over the last several years, we have developed a comprehensive program aimed at better understanding the properties of pulsating DA white dwarfs (or ZZ Ceti stars). These stars are nonradial pulsators of the g-type, and their study can lead to inferences about their internal structure. For instance, the period spectrum of a white dwarf is most sensitive to its vertical chemical stratification, and one of the major goals of white dwarf seismology is to determine the thickness of the hydrogen layer that sits on top of a star. This can be done, in principle, by comparing in detail theoretical period spectra with the periods of the observed excited modes. Likewise, because the cooling rate of a white dwarf is very sensitive to the specific heat of its core material (and hence to its composition), it is possible to infer the core composition through measurements and interpretations of rates of period change in a pulsator.

scholarly journals The internal structure of ZZ Cet stars using quantitative asteroseismology: The case of R548

2013 ◽  
Vol 9 (S301) ◽  
pp. 285-288
Author(s):  
N. Giammichele ◽  
G. Fontaine ◽  
P. Brassard ◽  
S. Charpinet
Keyword(s):  
Internal Structure ◽  
White Dwarf ◽  
White Dwarfs ◽  
Optimization Technique ◽  
Seismic Model ◽  
The Core ◽  
Spectroscopic Analyses ◽  
Core Composition ◽  
Oscillation Modes ◽  
Chemical Stratification

AbstractWe explore quantitatively the low but sufficient sensitivity of oscillation modes to probe both the core composition and the details of the chemical stratification of pulsating white dwarfs. Until recently, applications of asteroseismic methods to pulsating white dwarfs have been far and few, and have generally suffered from an insufficient exploration of parameter space. To remedy this situation, we apply to white dwarfs the same double-optimization technique that has been used quite successfully in the context of pulsating hot B subdwarfs. Based on the frequency spectrum of the pulsating white dwarf R548, we are able to unravel in a robust way the unique onion-like stratification and the chemical composition of the star. Independent confirmations from both spectroscopic analyses and detailed evolutionary calculations including diffusion provide crucial consistency checks and add to the credibility of the inferred seismic model. More importantly, these results boost our confidence in the reliability of the forward method for sounding white dwarf internal structure with asteroseismology.

scholarly journals Chemical Stratification in White Dwarf Atmospheres and Envelopes

1989 ◽  
Vol 114 ◽  
pp. 206-219
Author(s):  
D. Koester
Keyword(s):  
Equilibrium State ◽  
Elemental Composition ◽  
Electric Fields ◽  
White Dwarf ◽  
White Dwarfs ◽  
Observational Constraints ◽  
Chemical Stratification

The theory of gravitational separation of elements under the combined influence of gravity and electric fields (Schatzman 1958) has been very successful in explaining the general mono-elemental composition observed in most hot white dwarf atmospheres. Today the exceptions to the rule - DO and DAO with mixed compositions (Wesemael et al.1985), DA with traces of helium (Kahn et al. 1984, Petre et al. 1986, Jordan et al.1987, Paerels 1987), DAB (Liebert et al. 1984), and DBA (Shipman et al. 1987) - pose a problem, because they seem to demand a mechanism that counteracts gravitational separation. Such a mechanism that satisfies the observational constraints is very hard to find, and this has led in recent years to the growing conviction that we indeed observe the equilibrium state of diffusion, but in white dwarfs with extremely thin hydrogen layers that remain transparent (at least in the EUV) in many objects (Jordan and Koester 1986, Liebert et al.1987, Vennes et al. 1987, Fontaine et al.1988, Vennes et al.1988).

Star reaches out to white dwarf

Nature ◽  
2005 ◽  
Author(s):  
Roxanne Khamsi
Keyword(s):  
White Dwarf

Stellar Masses, Kinematics, and White Dwarf Composition for Three Close DA+dMe Binaries

1999 ◽  
Vol 523 (1) ◽  
pp. 386-398 ◽  
Author(s):  
Stephane Vennes ◽  
John R. Thorstensen ◽  
Elisha F. Polomski
Keyword(s):  
White Dwarf ◽  
Stellar Masses

Discovery of a Magnetic White Dwarf in the Symbiotic Binary Z Andromedae

1999 ◽  
Vol 517 (2) ◽  
pp. 919-924 ◽  
Author(s):  
J. L. Sokoloski ◽  
Lars Bildsten
Keyword(s):  
White Dwarf

scholarly journals WD 1856 b: a close giant planet around a white dwarf that could have survived a common envelope phase

2020 ◽  
Vol 501 (1) ◽  
pp. 676-682
Author(s):  
F Lagos ◽  
M R Schreiber ◽  
M Zorotovic ◽  
B T Gänsicke ◽  
M P Ronco ◽  
...  
Keyword(s):  
White Dwarf ◽  
Evolutionary History ◽  
Giant Planet ◽  
Asymptotic Giant Branch ◽  
Orbital Energy ◽  
Current Position ◽  
Recombination Energy ◽  
Additional Energy ◽  
Common Envelope ◽  
History Of

ABSTRACT The discovery of a giant planet candidate orbiting the white dwarf WD 1856+534 with an orbital period of 1.4 d poses the questions of how the planet reached its current position. We here reconstruct the evolutionary history of the system assuming common envelope evolution as the main mechanism that brought the planet to its current position. We find that common envelope evolution can explain the present configuration if it was initiated when the host star was on the asymptotic giant branch, the separation of the planet at the onset of mass transfer was in the range 1.69–2.35 au, and if in addition to the orbital energy of the surviving planet either recombination energy stored in the envelope or another source of additional energy contributed to expelling the envelope. We also discuss the evolution of the planet prior to and following common envelope evolution. Finally, we find that if the system formed through common envelope evolution, its total age is in agreement with its membership to the Galactic thin disc. We therefore conclude that common envelope evolution is at least as likely as alternative formation scenarios previously suggested such as planet–planet scattering or Kozai–Lidov oscillations.

Sign in / Sign up

Export Citation Format

Share Document