Spectral analyses of DO white dwarfs and PG 1159 stars from the Sloan Digital Sky Survey

¹ Institut für Astrophysik, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany e-mail: shuegelm@astro.physik.uni-goettingen.de
² Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
³ New Mexico State University, Apache Point Observatory, 2001 Apache Point Road, PO Box 59, Sunspot, NM 88349, USA
⁴ Mt. Suhora Observatory, Cracow Pedagogical University, ul. Podchorazych 2, 30-084 Cracow, Poland

Received: 21 April 2005
Accepted: 4 July 2005

Abstract

We present a model atmosphere analysis of ten new DO white dwarfs and five new PG 1159 stars discovered in the Sloan Digital Sky Survey DR1, DR2 and DR3. This is a significant increase in the number of known DOs and PG 1159 stars. DO white dwarfs are situated on the white dwarf cooling sequence from the upper hot end (T_eff K) down to the DB gap (T_eff K). PG 1159 stars on the other hand feature effective temperatures which exceed T_eff K with an upper limit of T_eff K and are the proposed precursors of DO white dwarfs. Improved statistics are necessary to investigate the evolutionary link between these two types of stars. From optical SDSS spectra effective temperatures, surface gravities and element abundances are determined by means of non-LTE model atmospheres.