Discovery of seven ZZ Ceti stars using a new photometric selection method

¹ Institut für Theoretische Physik und Astrophysik, Universität Kiel, Leibnizstraße 15, 24098 Kiel, Germany e-mail: voss@astrophysik.uni-kiel.de
² Isaac Newton Group, Apartado de correos 321, 38700 Santa Cruz de la Palma, Spain
³ Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-900 Porto Alegre, RS, Brazil
⁴ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁵ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁶ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 19 September 2005
Accepted: 28 November 2005

Abstract

We report the detection of non-radial g-mode oscillations in seven relatively bright () DA white dwarf stars from time-series photometry collected at the Nordic Optical Telescope (NOT) at Roque de Los Muchachos Observatory, Spain. The candidate variable stars were selected from preparatory photometric observations of objects from the Hamburg Quasar Survey (HQS) and from spectroscopy of stars from the Villanova (WD) catalogue. The selection of ZZ Ceti candidate stars from photometric data proved nearly as successful as the more common spectroscopic selection method. The effective temperatures that we derive from both methods are consistent with a pure ZZ Ceti instability strip.