Spectral analysis of sdB stars from the Hamburg Quasar Survey

We present the results of a spectral analysis of a large sample of sub dwarf B stars selected from follow-up observations of candidates from the Hamburg Quasar Survey. Fundamental parameters (effective temperature, gravity, and helium abundance) were determined by matching synthetic line profiles calculated from model atmospheres to all hydrogen and helium absorption lines present in the observed optical spectra. The derived helium abundances are compared with the atmospheric parameters to search for possible trends. We discovered a correlation between the helium abundance and the effective temperature: the larger the temperature, the larger the photospheric helium content of sdB stars. Additionally, a separation into two sequences of sdB stars in the effective temperature - helium abundance plane is detected. We compared our analysis results with data from the literature. The stars from our sample are found to be somewhat more luminous. This can only partly be explained by NLTE effects. Three apparently normal B stars were discovered, which could be massive stars far away from the galactic plane (7-19 kpc). Radial velocities were measured for 23 stars from which we discovered a new radial velocity variable sdB star.