An analysis of DA white dwarfs from the Hamburg Quasar Survey

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 Teff and log g, 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 B ≤ 16. m4 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 Teff > 50 000 K compared to other surveys. The mean mass of our DA sample is M=0.61M , with three massive DA stars exceeding 1M and three DA stars with masses significantly below the assummed lower mass limit for single white dwarf evolution of 0.45M . Among the cool DA stars, thirteen are potential ZZ Ceti candidates because their effective temperatures lie close to the instability strip.