UBV photometry of hot DA white dwarfs

Johnson UBV photometry has been obtained photoelectrically for a set of DA white dwarfs with effective temperatures greater than 20,000 K and for the AM Her type binary HO538 + 608. Most of the white dwarfs lie within existing Einstein IPC or EXOSAT LE soft X-ray fields, therefore they are of interest as potential serendipitous soft X-ray sources. In addition, high dispersion spectroscopy has been used to differentiate seven of these objects to be subdwarfs. 14 refs.