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EUVE and ORFEUS Observations of the Cool DO White Dwarf HD 149499 B

Published online by Cambridge University Press:  12 April 2016

R. Napiwotzki ,
S. Jordan ,
S. Bowyer ,
M. Hurwitz ,
D. Koester ,
T. Rauch  and
V. Weidemann
R. Napiwotzki
Affiliation:
Dr. Remeis-Sternwarte, Sternwartstr. 7, 96049 Bamberg, Germany
S. Jordan
Affiliation:
Institut für Astronomie und Astrophysik der Universität, 24098 Kiel, Germany
S. Bowyer
Affiliation:
Center for EUV Astrophysics, 2150 Kittredge Street, University of California, Berkeley, CA 94720-5030, USA
M. Hurwitz
Affiliation:
Center for EUV Astrophysics, 2150 Kittredge Street, University of California, Berkeley, CA 94720-5030, USA
D. Koester
Affiliation:
Institut für Astronomie und Astrophysik der Universität, 24098 Kiel, Germany
T. Rauch
Affiliation:
Institut für Astronomie und Astrophysik der Universität, 24098 Kiel, Germany
V. Weidemann
Affiliation:
Institut für Astronomie und Astrophysik der Universität, 24098 Kiel, Germany

Abstract

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We present the results of a recent spectroscopic investigation of the cool DO white dwarf HD 149499 B in the EUV and FUV ranges. Observations were performed with the spectrograph of the EUVE satellite and the Berkeley EUV/FUV spectrometer of the ORFEUS space experiment. The analysis of the ORFEUS spectrum, performed with a grid of LTE model atmospheres, yielded the basic parameters Teff = 49500 ± 500 K and log g = 7.97 ± 0.08. This result is confirmed by the EUVE spectra. The photospheric hydrogen Lyman lines in the FUV spectrum indicate the presence of hydrogen: log nH/nHe = −0.65 ± 0.12. The implications of this finding for the spectral evolution of white dwarfs are discussed. A check of the LTE assumption was performed by a comparison with NLTE atmospheres calculated for appropriate parameters. The interstellar hydrogen column towards the HD 149499 system amounts to NH = (7 ± 2) · 1018 cm−2.

Type
IV. White Dwarf Structure/Evolution
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 241 - 246
Copyright
Copyright © Kluwer 1996

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