The presence of helium in hot DA white dwarfs - The role of radiative levitation and the case for stratifies atmospheres

1988 ◽  
Vol 331 ◽  
pp. 876 ◽  
Author(s):  
S. Vennes ◽  
C. Pelletier ◽  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
White Dwarfs

scholarly journals Rapid destruction of planetary debris around white dwarfs through aeolian erosion

2021 ◽  
Vol 502 (4) ◽  
pp. 5176-5184
Author(s):  
Mor Rozner ◽  
Dimitri Veras ◽  
Hagai B Perets
Keyword(s):  
White Dwarfs ◽  
Extensive Study ◽  
Destructive Process ◽  
Rapid Destruction ◽  
Aeolian Erosion ◽  
Formation And Evolution ◽  
Destructive Processes ◽  
Solid Bodies ◽  
Erosive Effect

ABSTRACT The discovery of numerous debris discs around white dwarfs (WDs) gave rise to extensive study of such discs and their role in polluting WDs, but the formation and evolution of these discs is not yet well understood. Here, we study the role of aeolian (wind) erosion in the evolution of solids in WD debris discs. Aeolian erosion is a destructive process that plays a key role in shaping the properties and size distribution of planetesimals, boulders, and pebbles in gaseous protoplanetary discs. Our analysis of aeolian erosion in WD debris discs shows that it can also play an important role in these environments. We study the effects of aeolian erosion under different conditions of the disc and its erosive effect on planetesimals and boulders of different sizes. We find that solid bodies smaller than $\sim \! 5 \, \rm {km}$ will be eroded within the short disc lifetime. We compare the role of aeolian erosion in respect to other destructive processes such as collisional fragmentation and thermal ablation. We find that aeolian erosion is the dominant destructive process for objects with radius $\lesssim \! 10^3 \, \rm {cm}$ and at distances $\lesssim \! 0.6 \, \mathrm{R}_\odot$ from the WD. Thereby, aeolian erosion constitutes the main destructive pathway linking fragmentational collisions operating on large objects with sublimation of the smallest objects and Poynting–Robertson drag, which leads to the accretion of the smallest particles on to the photosphere of WDs, and the production of polluted WDs.

scholarly journals White dwarfs as astrophysical probes

2008 ◽  
Vol 4 (S258) ◽  
pp. 299-306
Author(s):  
Jasonjot S. Kalirai
Keyword(s):  
White Dwarfs ◽  
Elliptical Galaxies ◽  
Main Sequence Stars ◽  
Large White ◽  
Hydrogen Burning ◽  
Nearby Star ◽  
Stellar Ages ◽  
Initial Discovery ◽  
Uv Upturn

AbstractMuch of our knowledge regarding the ages of stars derives from our understanding of the Hertzsprung-Russell Diagram. The diagram is typically dominated by hydrogen burning main-sequence stars, which historically, have been used to establish our most fundamental knowledge of stellar ages and evolution. In this brief article, I highlight how deep ground and space based imaging can uncover the stellar remnants of these hydrogen burning stars, white dwarfs. We have followed up our initial discovery of several large white dwarf populations in nearby star clusters with multiobject spectrographs. The spectroscopy allows us to characterize the properties of the remnant stars (e.g., mass, temperature, and age), which are in turn used to shed new light on fundamental astrophysical problems. Specifically, we estimate the ages of the Milky Way disk and halo, provide the inputs needed to calculate the chemical evolution of galaxies, and re-iterate the important role of HB stars in producing the UV-upturn seen in elliptical galaxies.

Role of the interparticle interactions and axial rotation in the massive white dwarfs theory

2018 ◽  
Vol 8 (1) ◽  
pp. 9-15
Author(s):  
D. Dzikovskyi ◽  
M. Vavrukh ◽  
S. Smerechynskyi
Keyword(s):  
Equilibrium Equation ◽  
White Dwarfs ◽  
Axial Rotation ◽  
Nuclear Model ◽  
Universal Functions ◽  
Coulomb Interactions ◽  
Interparticle Interactions ◽  
Loss Of Mass ◽  
Radial Variable

Using the equation of state of electron-nuclear model at high densities and the mechanical equilibrium equation we have investigated the influence of interparticle interactions and axial rotation on the macroscopic characteristics of massive white dwarfs. The method of solving the equilibrium equation in the case of rotation, using the basis of universal functions of the radial variable has been proposed. The conditions in which the axial rotation can compensate for weight loss of mass due to the interparticle Coulomb interactions have been established.

scholarly journals Diffusion and Metal Abundances in Hot White Dwarfs Gerard Vauclair

1989 ◽  
Vol 114 ◽  
pp. 176-187 ◽  
Author(s):  
Gérard Vauclair
Keyword(s):  
Time Scales ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Metal Abundances ◽  
Cool White Dwarfs ◽  
First Time ◽  
Radiative Acceleration

While the efficiency of gravitational settling to produce chemically pure atmospheres in white dwarf stars was outlined for the first time 30 years ago (Schatzman 1958), the competing role of the radiation flux in the hot white dwarfs was considered only 10 years ago (Fontaine and Michaud 1979; Vauclair, Vauclair and Greenstein 1979). At that time, there was more motivation to understand how metals could reappear in the long lived cool non DA white dwarfs, where diffusion time scales are shorter by orders of magnitude than evolutionary time scales. Various processes were invoked to help restore some metal content in the white dwarf atmospheres: convection mixing and dredge up, accretion of interstellar matter. In cool white dwarfs, the radiative acceleration is negligeable in the diffusion process; this is not the case at the hot end of the sequence where radiation may balance gravity. The short lived hot white dwarfs just started to become exciting with the contemporary discoveries that i) some show metallic lines in their spectra, both hydrogen rich and hydrogen poor; ii) some of these are pulsating. In the following years, the number of hot white dwarfs revealing trace abundance of metals has increased, mainly owing to IUE observations.

scholarly journals The Composition and Structure of White Dwarf Atmospheres Revealed by Extreme Ultraviolet Spectroscopy

1996 ◽  
Vol 152 ◽  
pp. 203-210
Author(s):  
Martin A. Barstow ◽  
Ivan Hubeny ◽  
Thierry Lanz ◽  
Jay B. Holberg ◽  
Edward M. Sion
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Extreme Ultraviolet ◽  
Important Change ◽  
Heavy Elements ◽  
Composition And Structure ◽  
Crucial Test ◽  
Central Stars ◽  
Quantitative Consideration

The ROSAT and EUVE all-sky surveys have resulted in an important change in our understanding of the general composition of hydrogen-rich DA white dwarf atmospheres, with the photospheric opacity dominated by heavy elements rather than helium in the hottest stars (T > 40, 000 K). Most stars cooler than 40,000 K have more or less pure H atmospheres. However, one question, which has not been resolved, concerned the specific nature of the heavy elements and the role of helium in the hottest white dwarfs. One view of white dwarf evolution requires that H-rich DA stars form by gravitational settling of He from either DAO or He-rich central stars of planetary nebulae. In this case, the youngest (hottest) DA white dwarfs may still contain visible traces of He. Spectroscopic observations now available with EUVE provide a crucial test of these ideas. Analysis of data from the EUVE Guest Observer programme and EUVE public archive allows quantitative consideration of the sources of EUV opacity and places limits on the abundance of He which may be present.

The role of G in the cooling of white dwarfs

2008 ◽  
pp. 73-77
Author(s):  
Enrique García-Berro ◽  
Margarita Hernanz ◽  
Jordi Isern ◽  
Robert Mochkovitch
Keyword(s):  
White Dwarfs

scholarly journals Equilibrium Abundances of Heavy Elements Supported by Radiative Levitation in the Atmospheres of Hot DA White Dwarfs

1996 ◽  
Vol 152 ◽  
pp. 211-215
Author(s):  
P. Chayer ◽  
S. Vennes ◽  
A.K. Pradhan ◽  
P. Thejll ◽  
A. Beauchamp ◽  
...  
Keyword(s):  
Line Profile ◽  
White Dwarfs ◽  
Heavy Elements ◽  
Background Plasma ◽  
Pressure Broadening ◽  
Opaque Material ◽  
Trace Pollutants ◽  
Flux Redistribution

We present revised estimates of the equilibrium abundances of heavy elements supported by radiative levitation in the atmospheres of hot DA white dwarfs. We emphasize, in particular, the role of trace pollutants that may be present in the background plasma, an effect which has been heretofore neglected. We take advantage of the availability of a table of detailed monochromatic opacities calculated for a plasma made of H containing small amounts of C, N, O, and Fe to illustrate how the equilibrium abundances of levitating elements react to the flux redistribution caused by the addition of these small traces of opaque material. We also consider two other improvements: a more sophisticated treatment of the momentum redistribution process and ion experiences following a photoexcitation, and use of an upgraded value for the line profile width associated with pressure broadening.

scholarly journals SUPERNOVAE FROM DIRECT COLLISIONS OF WHITE DWARFS AND THE ROLE OF HELIUM SHELL IGNITION

2016 ◽  
Vol 822 (1) ◽  
pp. 19 ◽  
Author(s):  
Oded Papish ◽  
Hagai Binyamin Perets
Keyword(s):  
White Dwarfs

scholarly journals THE ROLE OF WHITE DWARFS IN CATACLYSMIC VARIABLE SPIN-DOWN

2012 ◽  
Vol 746 (1) ◽  
pp. L3 ◽  
Author(s):  
O. Cohen ◽  
J. J. Drake ◽  
V. L. Kashyap
Keyword(s):  
White Dwarfs ◽  
Cataclysmic Variable ◽  
Variable Spin

scholarly journals Accretion on to highly magnetized white dwarfs: the role of electron conduction

1980 ◽  
Vol 191 (4) ◽  
pp. 721-728 ◽  
Author(s):  
A. R. King ◽  
J. P. Lasota
Keyword(s):  
White Dwarfs ◽  
Electron Conduction
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