LONG-TERM VARIABILITY OF THE BE X-RAY BINARY A-0535+26 - I - OPTICAL AND UV SPECTROSCOPY/

The results of a 7-yr optical and UV spectroscopic study of the high-m ass X-ray binary A 0535 + 26 are presented. It was found that througho ut the period of the observations the line profile of H alpha showed c onsiderable variability, A correlation between the equivalent width of H alpha and both V-band magnitude and (B-V) colour excess was observe d, albeit with considerable scatter present in the data set. A giant X -ray flare in early 1994 was accompanied by a fading in optical and in frared photometric bands, and a reduction in the equivalent width of H alpha. When the star was observed in 1994 September, it was found to have developed a double-peaked H alpha profile, and further observatio ns saw the V/R peak ratio vary cyclically, with a period of similar to 1 yr. If this is identified as a global one-armed oscillation, it bec omes the shortest period ever observed in a Be star. The accompanying photometric and spectroscopic observations provide a test of any theor y seeking to describe the onset and behaviour of such a density wave.