Systematics of hot subdwarfs obtained from a large low resolution survey

![CDATA[We have recently completed a low resolution spectroscopic survey of several hundred subdwarf B, subdwarf O, blue horizontal branch, and postasymptotic giant branch stars. Homogeneous effective temperatures, surface gravities and helium abundances were derived by fitting Balmer and helium lines using a large grid of NLTE zero-metallicity atmospheres. The survey is complete for known hot subdwarf candidates in the northern hemisphere brighter than about 14.2. We used the same spectra to derive multiple radial velocities for a large fraction of the hot subdwarfs, in order to investigate patterns of radial velocity variability in the surface gravity – effective temperature plane, and also in the V −J vs. J−H diagram. We present several examples illustrating how the binary characteristics of hot subdwarfs, as functions of temperature, gravity and color, can be used to set important constraints on their formation and evolution.]]