PI: Noemi Giammichele, University of Montreal, email@example.com
Address: Physics Department, C.P. 6128, succ. Centre-Ville, Montreal, Quebec H3C 3J7, Canada
CoI: Pierre Bergeron, University of Montreal
Title: Understanding the Spectral Evolution of Helium-Line DB White Dwarfs
Abstract: DB white dwarfs have spectra dominated by neutral helium lines, with the occasional presence of weak hydrogen features (DBA stars). It is commonly accepted that the progenitors of DB white dwarfs are hotter hydrogen-line DA stars whose thin hydrogen atmosphere has been convectively mixed with the deeper and more massive helium convection zone. Detailed evolutionary models support this scenario, but residual amounts of hydrogen are also expected at the photosphere of DB stars. We have recently completed a detailed model atmosphere analysis of over 100 DB stars and showed that a significant fraction of these objects show no traces of hydrogen whatsoever, \it a result that suggests a second evolutionary channel for DB stars. Unfortunately, this picture is confused by the fact that over 40 objects in our sample lack the H(alpha) coverage required to properly constrain the hydrogen abundances in these stars. We obtained during the last semester run (2012A) high signal-to-noise spectra covering the H(alpha) region for 21 white dwarfs, and we propose to cover the remaining 20 missing white dwarfs, in order to get the clearest picture of the spectral evolution of DB stars ever achieved, as well as a better understanding of their possible evolutionary channels.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360