ON THE EXISTENCE OF DA,F WHITE-DWARFS

The ideas and work presented in this paper date almost entirely from 1977 when the original paper was submitted. The referee suggested that we check out several other strong northern candidates before publication, but upon resubmission several years later the editor noted that as it was now accepted that DA,F white dwarfs did not exist there was little point in publishing the paper. In view of the fact that our preprint was the main stimulus for this status change and reference to this work remains '1977 unpublished', we would like the paper to be published and thus complete the historical record. Observations of some of the stars considered by Weidemann as the most likely DA,F candidates are discussed together with theoretical computations of white dwarfs and subdwarfs. The reddest stars BPM 23251 and G 82-23 are shown to be K subdwarfs and L 532-81 (EG62) is a DA white dwarf. It is suggested that the DA,F stars, if they exist at all, are extremely rare and that the metal abundance of the DA sequence may be less than 10-4 of the solar abundance.