Effective Temperatures of White Dwarfs

White Dwarfs ◽  
1971 ◽  
pp. 67-76 ◽  
Author(s):  
J. B. Oke ◽  
H. L. Shipman
Keyword(s):  
White Dwarfs ◽  
Effective Temperatures

scholarly journals FAR-Ultralviolet Spectrophotometry of two do White Dwarfs from Voyager

1989 ◽  
Vol 114 ◽  
pp. 144-148
Author(s):  
E. Poulin ◽  
F. Wesemael ◽  
J.B. Holberg ◽  
G. Fontaine
Keyword(s):  
Binary System ◽  
White Dwarfs ◽  
Temperature Scale ◽  
Classification Scheme ◽  
The Other ◽  
Other Hand ◽  
Effective Temperatures

While the observed number of hot, helium-rich degenerates is noticeably larger than that of their hydrogen-rich counterparts, the calibration of their effective temperatures has been comparatively much less trustworthy. The spectroscopic classification scheme introduced three years ago by Wesemael, Green, and Liebert (1985, hereafter WGL), and the crude temperature domains associated with each class remain, to this date, the only comprehensive effort at defining a temperature scale for DO stars. The current uncertainty in this is perhaps best epitomized by two objects, HD149499B and PG1034+001. The former belongs to a binary system which also contains a KO V primary, 2” away. The temperature determined for the degenerate secondary ranges from 85,000±15,000 K (Wray, Parsons, and Henize 1979) to 55,000±5000 K (Sion, Guinan, and Wesemael 1982, hereafter SGW). PG1034+001, on the other hand, is the prototype of the so-called hot DO spectroscopic class; WGL assign an uncertain temperature of 80,000±20,000 K to this object.

scholarly journals The Effective Temperature Distribution Function of Cataclysmic Variable White Dwarfs

1987 ◽  
Vol 93 ◽  
pp. 47-51
Author(s):  
E.M. Sion
Keyword(s):  
Distribution Function ◽  
Temperature Distribution ◽  
Orbital Period ◽  
White Dwarf ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Cataclysmic Variable ◽  
Term Evolution ◽  
Effective Temperatures

AbstractWith the recent detection of direct white dwarf photospheric radiation from certain cataclysmic variables in quiescent (low accretion) states, important implications and clues about the nature and long-term evolution of cataclysmic variables can emerge from an analysis of their physical properties. Detection of the underlying white dwarfs has led to a preliminary empirical CV white dwarf temperature distribution function and, in a few cases, the first detailed look at a freshly accreted while dwarf photosphere. The effective temperatures of CV white dwarfs plotted versus orbital period for each type of CV appears to reveal a tendency for the cooler white dwarf primaries to reside in the shorter period systems. Possible implications are briefly discussed.

scholarly journals Model Atmospheres for Very Cool Hydrogen-Rich White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 236-239
Author(s):  
France C. Allard ◽  
Rainer Wehrse
Keyword(s):  
White Dwarfs ◽  
Gas Pressure ◽  
Special Consideration ◽  
Solar Photosphere ◽  
Energy Distributions ◽  
Effective Temperatures ◽  
Cool White Dwarfs

In recent years cool white dwarfs have been studied for various aspects ( see e.g.Winget et al.,1987 Winget and van Horn, 1987, Koester, 1987, Llebert, 1980) and much effort has been Invested in attempts to interpret the energy distributions of these stars ( Greenstein, 1984, Zeldler-K.T. et al, 1986, Llebert et al., 1987, and others). However, it seems that in spite of these efforts the spectra in particular of the very cool objects with effective temperatures below about 6000 K are not yet fully under-stood, since they are extremely diverse and each objects needs special consideration. In addition, the analyses are extremely difficult because the principal constiuents of the atmospheres ( H, He ) and elements, which may donate the majority of electrons, are essentially invisible. Since usually only one ionlsatlon stage of an element is present, this implies that the gas pressure Pg is high ( compared e.g. to the solar photosphere ), the accurate value of Pg, however, cannot be determined reliably.

Spectroscopic Studies and Atmospheric Parameters of ZZ Ceti Stars

1989 ◽  
Vol 114 ◽  
pp. 244-248
Author(s):  
D. Daou ◽  
F. Wesemael ◽  
P. Bergeron ◽  
G. Fontaine ◽  
J. B. Holberg
Keyword(s):  
Strong Evidence ◽  
White Dwarfs ◽  
Narrow Range ◽  
Spectroscopic Studies ◽  
Atmospheric Parameters ◽  
Instability Strip ◽  
Pulsating Stars ◽  
Evolutionary Phase ◽  
Effective Temperatures

The pulsating ZZ Ceti stars cover a narrow range of effective temperatures along the cooling sequence of DA white dwarfs (see, eg., Winget and Fontaine 1982). Fast-photometric searches for pulsating stars in that class have provided strong evidence that the ZZ Ceti phase is an evolutionary phase through which all cooling DA stars will eventually go through (Fontaine et al. 1982). Recent investigations, based on optical or ultraviolet photometry and spectrophotometry, have set the boundaries of the instability strip at temperatures near 10,000-11,000 K and 12,000-13,000 K, respectively (McGraw 1979; Greenstein 1982; Weidemann and Koester 1984; Fontaine et al. 1985; Wesemael, Lamontagne, and Fontaine 1986; Lamontagne, Wesemael, and Fontaine 1987, 1988).

scholarly journals Search For Cool White Dwarf Pulsators

2000 ◽  
Vol 176 ◽  
pp. 525-526
Author(s):  
Atsuko Nitta ◽  
A. Mukadam ◽  
D. E. Winget ◽  
A. Kanaan ◽  
S. J. Kleinman ◽  
...  
Keyword(s):  
Lower Limit ◽  
White Dwarf ◽  
White Dwarfs ◽  
Galactic Disk ◽  
Chemical Compositions ◽  
Physical Processes ◽  
Effective Temperatures

AbstractWe are searching for pulsations in cool (< 6000 K) white dwarfs (WDs), hoping to apply asteroseismological techniques to improve our understanding of their structure and the physical processes inside them. This information is important as we use cool WDs to estimate the lower limit of the age of the Galactic disk. Within a spectroscopic and photometric survey of 110 cool WDs by Bergeron, Ruiz, & Legget, we find 28 candidates with appropriate effective temperatures, masses, and chemical compositions for possible pulsations in nonradial g modes with periods similar to those we observe in DAVs. So far, we have observed 4 candidates, but have found no evidence of large variation.

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 New model atmosphere analyses of cool white dwarfs: a revised luminosity function and constraints on the age of the Galaxy

1997 ◽  
Vol 189 ◽  
pp. 429-432
Author(s):  
S.K. Leggett ◽  
P. Bergeron ◽  
Maria Teresa Ruiz
Keyword(s):  
White Dwarfs ◽  
Luminosity Function ◽  
State Of The Art ◽  
Model Atmosphere ◽  
Quality Data ◽  
High Quality Data ◽  
The Galaxy ◽  
Effective Temperatures ◽  
Cool White Dwarfs ◽  
Turn Over

We have obtained new photometric and spectroscopic data for a large sample of cool white dwarfs. These data have been analysed with state-of-the-art model atmospheres and effective temperatures and atmospheric compositions have been determined (Bergeron, Ruiz & Leggett 1997). Radii and masses have also been obtained for those stars with accurate parallax measurements. These high quality data and models allow us to produce an improved cool white dwarf luminosity function based on the Liebert, Dahn & Monet (1988) proper motion sample. The turn-over seen at the faint end of this luminosity function, combined with theoretical cooling sequences, enable us to constrain the age of the local region of the Galaxy.

scholarly journals Hot Subluminous Stars

1980 ◽  
Vol 5 ◽  
pp. 255-262
Author(s):  
Jesse L. Greenstein
Keyword(s):  
Mass Loss ◽  
Accretion Disk ◽  
Excellent Agreement ◽  
White Dwarf ◽  
White Dwarfs ◽  
Close Binary ◽  
Maximum Temperature ◽  
Effective Temperatures ◽  
Line Strengths

Extensive mass loss is observed for hot subluminous stars, through P Cygni lines in the ultraviolet. This persists in some sub-dwarf 0 stars, but is generally not observed in white dwarfs. The ultraviolet provides determination of effective temperatures. Among nine sdO’s, the maximum temperature reported is definitely below 60, 000 K; an object at 100, 000 K would be distinguishable. The sdO’s show a wide variety of line strengths, notably in N V, C IV and Si TV, as well as He II. One halo sdB is reported as rich in peculiar elements; it shows anomalous N V for its temperature. The comparison of effective temperatures of white dwarfs observed from space and from the ground gives excellent agreement. The hottest white dwarfs are near 60, 000 K, although one (helium-rich) reaches 80, 000 K. Another helium-rich close binary probably has an accretion disk; it is the only white dwarf to show the expanding shell of N V, C IV, Si IV characteristic of some subdwarfs. Two magnetic white dwarfs have been observed; one has strong unidentifiable features and the smallest known radius.

scholarly journals Effective temperatures of cataclysmic-variable white dwarfs as a probe of their evolution

2016 ◽  
Vol 466 (3) ◽  
pp. 2855-2878 ◽  
Author(s):  
A. F. Pala ◽  
B. T. Gänsicke ◽  
D. Townsley ◽  
D. Boyd ◽  
M. J. Cook ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Cataclysmic Variable ◽  
Effective Temperatures

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.

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