Studies of hot B subdwarfs. I - Stromgren photometry of the Greenstein-Sargent-sample

Strömgren colors for a sample of 25 hot B subdwarfs are presented. These stars form a well-defined sequence in a two-color diagram, the existence of which is shown to be consistent with the evolutionary scenario for sdB stars proposed by Wesemael et al. (1982). A comparison of the photometric data with appropriate model atmosphere calculations suggests that hot B subdwarfs have effective temperatures ranging from 25000K to upward of 40000K, and surface gravities generally above log g = 5.0.