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Astron. Astrophys. 338, 563-575 (1998)


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An analysis of DA white dwarfs from the Hamburg Quasar Survey *

D. Homeier 1, D. Koester 1, H.-J. Hagen 2, S. Jordan 1, U. Heber 3, D. Engels 2, D. Reimers 2 and S. Dreizler 4

1 Institut für Theoretische Physik und Astrophysik der Christian-Albrechts-Universität, Leibnizstraße 15, D-24098 Kiel, Germany (homeier,koester,jordan@astrophysik.uni-kiel.de)
2 Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany (hhagen,dengels,dreimers@hs.uni-hamburg.de)
3 Dr.-Remeis-Sternwarte Bamberg, Universität Erlangen-Nürnberg, Sternwartstraße 7, D-96049 Bamberg, Germany (heber@sternwarte.uni-erlangen.de)
4 Institut für Astronomie und Astrophysik, Waldhäuser Straße 64, D-72076 Tübingen, Germany (dreizler@astro.uni-tuebingen.de)

Received 30 March 1998 / Accepted 22 June 1998

Abstract

Follow-up spectroscopy of several hundred hot stars detected by the Hamburg Quasar Survey (HQS) has been carried out between 1989 and 1996. We present the analysis of 80 DA white dwarfs using model atmospheres and theoretical cooling tracks to derive the atmospheric parameters [FORMULA] and [FORMULA], masses and absolute magnitudes. The HQS turned out to be sensitive to the detection of hydrogen-rich white dwarfs in a wide temperature range, from 10 000 K upwards. Star counts within four HQS fields for magnitudes [FORMULA] exceed those from the Palomar Green survey by about 50%. The more recent observation campaigns emphasized the detection of very hot degenerates, yielding a large fraction of DA stars with [FORMULA] [FORMULA] 50 000 K compared to other surveys. The mean mass of our DA sample is M=0.61[FORMULA], with three massive DA stars exceeding 1[FORMULA] and three DA stars with masses significantly below the assummed lower mass limit for single white dwarf evolution of 0.45[FORMULA]. Among the cool DA stars, thirteen are potential ZZ Ceti candidates because their effective temperatures lie close to the instability strip.

Key words: white dwarfs – stars: statistics – surveys

* Based on observations collected at the German-Spanish Astronomical Center (DSAZ), Calar Alto, operated by the Max-Plank-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy; with the International Ultraviolet Explorer satellite (IUE) collected at Villafranca, Spain, and with the ROSAT X-ray telescope.

Send offprint requests to: D. Homeier

© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998

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