Limits on the space density of O subdwarfs and hot white dwarfs from a search for extreme ultraviolet sources

1976 ◽  
Vol 205 ◽  
pp. 426 ◽  
Author(s):  
P. Henry ◽  
S. Bowyer ◽  
M. Lampton ◽  
F. Paresce ◽  
R. Cruddace
Keyword(s):  
White Dwarfs ◽  
Extreme Ultraviolet ◽  
Space Density

scholarly journals A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars

1996 ◽  
Vol 152 ◽  
pp. 217-222
Author(s):  
Jean Dupuis ◽  
Stéphane Vennes
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Heavy Element ◽  
Extreme Ultraviolet ◽  
Diffusion Theory ◽  
Hydrogen Atmosphere ◽  
Element Abundance ◽  
Pure Hydrogen ◽  
Element Abundances ◽  
The One

We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.

scholarly journals Expected Scientific Performance of the Three Spectrometers on the Extreme Ultraviolet Explorer

1990 ◽  
Vol 115 ◽  
pp. 335-338
Author(s):  
J. V. Vallerga ◽  
P. Jelinsky ◽  
P. W. Vedder ◽  
R. F. Malina
Keyword(s):  
Wavelength Range ◽  
Spectral Resolution ◽  
Line Source ◽  
White Dwarfs ◽  
Extreme Ultraviolet ◽  
Cataclysmic Variables ◽  
Effective Area ◽  
Light Sources ◽  
Scientific Performance ◽  
Astronomical Satellite

AbstractThe expected in-orbit performance of the three spectrometers included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite is presented. Recent calibrations of the gratings, mirrors and detectors using monochromatic and continuum EUV light sources allow the calculation of the spectral resolution and throughput of the instrument. An effective area range of 0.2 to 2.8 cm2 is achieved over the wavelength range 70-600Å with a peak spectral resolution λ/Δλ (FWHM) of ~ 360 assuming a spacecraft pointing knowledge of 10 arc seconds (FWHM). For a 40,000 sec observation, the average 3σ sensitivity to a monochromatic line source is 3 × 103 photons cm-2 sec-1. Simulated observations of known classes of EUV sources such as hot white dwarfs and cataclysmic variables are also presented.

scholarly journals Three Double Degenerate Candidates

1989 ◽  
Vol 114 ◽  
pp. 163-166
Author(s):  
Diana Foss
Keyword(s):  
Radial Velocity ◽  
Lower Limit ◽  
White Dwarfs ◽  
Radial Velocities ◽  
Close Binary ◽  
Space Density ◽  
Velocity Variations

This poster reports the results of a search for variable radial velocities in 29 DA white dwarfs. The survey was sensitive to periods between 1h and 66d, although non-ideal sampling limited the longest practically detectable period to 2d. Three stars were discovered to have radial velocity shifts at above the 3σ level. The discovery of these stars, along with that of Saffer, et al. (1988) can put only a lower limit on the space density of close binary white dwarfs, as this survey was less than 100% efficient in detecting radial velocity variations, and its efficiency depended strongly on period.

scholarly journals Selection Functions in Astronomical Data Modeling, with the Space Density of White Dwarfs as a Worked Example

2021 ◽  
Vol 162 (4) ◽  
pp. 142
Author(s):  
Hans-Walter Rix ◽  
David W. Hogg ◽  
Douglas Boubert ◽  
Anthony G. A. Brown ◽  
Andrew Casey ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Data Modeling ◽  
Space Density ◽  
Astronomical Data ◽  
Worked Example

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

EUV Radiation from Hot Star Photospheres: Theory Versus Observations

1996 ◽  
Vol 152 ◽  
pp. 381-388
Author(s):  
Ivan Hubeny ◽  
Thierry Lanz
Keyword(s):  
Ultraviolet Radiation ◽  
White Dwarfs ◽  
Extreme Ultraviolet ◽  
Theoretical Interest ◽  
Paper Briefly ◽  
Hot Stars ◽  
B Stars ◽  
Theory Versus ◽  
Stellar Photosphere ◽  
Extreme Ultraviolet Radiation

The only stars other than white dwarfs whose photospheric extreme ultraviolet radiation has been detected are ϵ and β CMa. It is therefore of considerable theoretical interest to compare the EUVE observations of these two giant B stars to predicted spectra. However, both LTE and non-LTE very sophisticated line blanketed model atmospheres fail to match the observed flux. This failure leaves the stellar photosphere theory, even for seemingly “simple” objects as normal B giants were believed to be, in a rather dubious position. This paper briefly summarizes possible reasons for the failure of existing models to describe the EUVE observations of hot stars. In particular, we discuss the effects of uncertainties in the line blanketing, and the effects of the photosphere-wind interaction.

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