An encoder system for the 18-inch telescope and uvbyHB photometry of bright UV stars

An observation program of uvbyHB photometry was performed on 90 stars taken from Garnochan and Wilson»s (1976) catalogue of objects that appear to be very ultraviolet as detected by the S2/68 experiment in the ESRO TD-1A satellite. The classification of most of the stars by visible photometry, published spectrographic class, and ultraviolet photometry from the TD-1A data is consistent to within two subclasses. The initial appearance of excessive UV for these objects would appear to be due to incorrect HD classification. Two objects (HD36629 and HD81307) appear to have genuinely excessive ultraviolet flux, and it is suggested that this could be due to the presence of faint, hot companions with size and luminosity comparable to planetary nebulae. A few stars show peculiarities for which there is no obvious explanation. An examination is made of the suggestion of Garnochan and Wilson (1983) that a large number of the objects in Wilson^s (1978) catalogue with very ultraviolet colours are subdwarfs, with luminosities two magnitudes below the" main sequence. It is shown that the results of this program do not support the suggestion,