A Comparative Study of the Atmospheric Composition of the DA White Dwarfs Feige 24 and G191‐B2B

2001 ◽  
Vol 553 (1) ◽  
pp. 399-404 ◽  
Author(s):  
Stephane Vennes ◽  
Thierry Lanz
Keyword(s):  
Comparative Study ◽  
White Dwarfs ◽  
Atmospheric Composition

Diffusion in white dwarfs - New results and comparative study

1986 ◽  
Vol 61 ◽  
pp. 197 ◽  
Author(s):  
C. Paquette ◽  
C. Pelletier ◽  
G. Fontaine ◽  
G. Michaud
Keyword(s):  
Comparative Study ◽  
White Dwarfs

scholarly journals A Comparative Study of the Mass Distribution of Extreme‐Ultraviolet–selected White Dwarfs

1999 ◽  
Vol 517 (1) ◽  
pp. 399-415 ◽  
Author(s):  
R. Napiwotzki ◽  
Paul J. Green ◽  
Rex A. Saffer
Keyword(s):  
Comparative Study ◽  
Mass Distribution ◽  
White Dwarfs ◽  
Extreme Ultraviolet

scholarly journals An Isolated White Dwarf with a 70 s Spin Period

2021 ◽  
Vol 923 (1) ◽  
pp. L6
Author(s):  
Mukremin Kilic ◽  
Alekzander Kosakowski ◽  
Adam G. Moss ◽  
P. Bergeron ◽  
Annamarie A. Conly
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
White Dwarfs ◽  
Tangential Velocity ◽  
Large Mass ◽  
Atmospheric Composition ◽  
Instability Strip ◽  
Detailed Model ◽  
Helium Atmosphere ◽  
Spin Period

Abstract We report the discovery of an isolated white dwarf with a spin period of 70 s. We obtained high-speed photometry of three ultramassive white dwarfs within 100 pc and discovered significant variability in one. SDSS J221141.80+113604.4 is a 1.27 M ⊙ (assuming a CO core) magnetic white dwarf that shows 2.9% brightness variations in the BG40 filter with a 70.32 ± 0.04 s period, becoming the fastest spinning isolated white dwarf currently known. A detailed model atmosphere analysis shows that it has a mixed hydrogen and helium atmosphere with a dipole field strength of B d = 15 MG. Given its large mass, fast rotation, strong magnetic field, unusual atmospheric composition, and relatively large tangential velocity for its cooling age, J2211+1136 displays all of the signatures of a double white dwarf merger remnant. Long-term monitoring of the spin evolution of J2211+1136 and other fast-spinning isolated white dwarfs opens a new discovery space for substellar and planetary mass companions around white dwarfs. In addition, the discovery of such fast rotators outside of the ZZ Ceti instability strip suggests that some should also exist within the strip. Hence, some of the monoperiodic variables found within the instability strip may be fast-spinning white dwarfs impersonating ZZ Ceti pulsators.

scholarly journals Toward a Determination of the Helium Abundance in Cool Da White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 430-434
Author(s):  
P. Bergeron ◽  
F. Wesemael ◽  
G. Fontaine
Keyword(s):  
White Dwarfs ◽  
Atmospheric Composition ◽  
Helium Abundance ◽  
Convective Mixing ◽  
Cool Stars ◽  
Effective Temperatures ◽  
Exact Amount

Connective mixing between the thin superficial hydrogen layer and the more massive and deeper helium layer is generally believed to be responsible for the increased number of non-DA white dwarfs relative to the number of DA below 10000K (see Sion 1984 and references therein). However, because of the spectroscopic invisibility of the helium lines at effective temperatures below 13000K, the true atmospheric composition of these cool stars remains somewhat uncertain. On theoretical grounds, studies of the evolution of white dwarfs on the cooling sequence have shown that if the hydrogen layer is thicker than ~10”6Me, convective mixing does not occur (Tassoul, Fontaine, and Winget 1988). Furthermore, the exact amount of helium pollution is very sensitive to the thickness of the hydrogen layer. It seems therefore imperative to evaluate to what extent DA stars below 13000K truly are hydrogen-rich. In line with our previous efforts geared toward an understanding of the atmospheric properties of the cool DA white dwarfs, we present new insights into the spectroscopic modelling of these cool stars, and also demonstrate, for a particular object, how the helium abundance might be determined.

The spectral evolution of hot white dwarfs

2019 ◽  
Vol 15 (S357) ◽  
pp. 162-165
Author(s):  
Antoine Bédard ◽  
Pierre Bergeron ◽  
Gilles Fontaine
Keyword(s):  
White Dwarfs ◽  
Spectroscopic Analysis ◽  
State Of The Art ◽  
Sloan Digital Sky Survey ◽  
Atmospheric Composition ◽  
Spectral Evolution ◽  
Sky Survey

AbstractAs they evolve, white dwarfs undergo major changes in their atmospheric composition, a phenomenon known as spectral evolution. In particular, most hot He-rich (DO) stars transform into H-rich (DA) stars as they cool off, most likely as a result of the float-up of residual H. We investigate this DO-to-DA transition by taking advantage of the extensive spectroscopic dataset provided by the Sloan Digital Sky Survey (SDSS). Using our new state-of-the-art non-LTE model atmospheres, we perform a spectroscopic analysis of 1882 hot (Teff >30,000 K) white dwarfs identified in the SDSS. We find that at least 15% of all white dwarfs are born with a He-dominated atmosphere. Among these, ∼2/3 turn into H-rich stars before they reach Teff ∼40,000 K, while the remaining ∼1/3 maintain their He-rich surface throughout their entire evolution. We speculate on the origin of these two groups of objects.

scholarly journals Time-Dependent Studies of the Settling of Heavy Elements in the Envelopes of Cool White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 359-362
Author(s):  
J. Dupuis ◽  
C. Pelletier ◽  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
Time Scales ◽  
White Dwarfs ◽  
Time Dependent ◽  
Heavy Elements ◽  
Atmospheric Composition ◽  
Element Abundance ◽  
Gravitational Settling ◽  
Observational Fact ◽  
Qualitative Conclusion ◽  
Cool White Dwarfs

Gravitational settling is widely accepted as being a fundamental physical process acting upon superficial layers of white dwarfs and resulting in an important alteration of their atmospheric composition. Several investigators have been interested by the problem of gravitational settling in white dwarfs (Fontaine and Michaud 1979; Vauclair, Vauclair, and Greenstein 1979; Alcock and Illarianov 1980; Muchmore 1984; Paquette et al. 1986). As pointed out in Paquette et al. 1986, they all reached the same qualitative conclusion: the gravitational settling time scales of metals in cool white dwarfs are small compared to their evolutionary time scales. These stars should therefore have their photospheres depleted of metals if there is no extrinsic source such as accretion for example. This is consistent with the observational fact that most of the cool white dwarfs spectra just show hydrogen and helium lines while the absence of metallic lines indicates a strong depletion of metals. Although the qualitative agreement between theory and observations is satisfactory, only time-dependent calculations can lead to a thorough understanding of the heavy element abundance patterns in cool white dwarfs. In particular, the predicted abundance of an element within the framework of the accretion-diffusion model does depend explicitly on the results of such calculations. We have already presented some preliminary results of numerical simulation of accretion episodes of heavy elements into white dwarfs (Dupuis et al. 1987). As part of an ongoing detailed investigation of these processes, we focus here exclusively on the mechanism of gravitational settling in white dwarfs in order to clear some confusion which has appeared in the literature.

scholarly journals GD 424 – a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal

2020 ◽  
Author(s):  
Paula Izquierdo ◽  
Odette Toloza ◽  
Boris T Gänsicke ◽  
Pablo Rodríguez-Gil ◽  
Jay Farihi ◽  
...  
Keyword(s):  
Steady State ◽  
Effective Temperature ◽  
White Dwarf ◽  
Metal Pollution ◽  
White Dwarfs ◽  
Surface Gravity ◽  
Atmospheric Composition ◽  
Atmospheric Parameters ◽  
Hybrid Analysis ◽  
Helium Atmosphere

Abstract The photospheric metal pollution of white dwarfs is now well-established as the signature of the accretion of planetary debris. However, the origin of the trace hydrogen detected in many white dwarfs with helium atmospheres is still debated. Here, we report the analysis of GD 424: a metal-polluted, helium-atmosphere white dwarf with a large amount of trace hydrogen. We determined the atmospheric parameters using a hybrid analysis that combines the sensitivity of spectroscopy to the atmospheric composition, log (H/He), with that of photometry and astrometry to the effective temperature, Teff, and surface gravity, log g. The resulting white dwarf mass, radius, and cooling age are ${M_{\rm{WD}}}=0.77\pm 0.01\, {\rm{M}_{\odot}}$, ${R_{\rm{WD}}}=0.0109\pm 0.0001\, {\rm{R}_{\odot}}$, and τcool = 215 ± 10 Myr, respectively. We identified and measured the abundances of 11 photospheric metals and argue that the accretion event is most likely either in the increasing or steady state, and that the disrupted planetesimal resembles either CI chondrites or the bulk Earth in terms of its composition. We suggest that the observed 1.33 × 1022 g of trace hydrogen in GD 424 were at least partly acquired through accretion of water-rich planetary debris in an earlier accretion episode.

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