Recent phase changes in X Persei: optical, infrared and X-ray behaviour

We present a set of optical and IR photometric measurements which show the lightcurve of the Be/X-ray binary system X Persei over the last 25 yr. During this period, the Be star has undergone two extended faint, nonvariable phases, the last of which (1990-present) has been shown to be related to the loss of the circumstellar shell associated with such systems. We show the relation between the presence of such a disk and the variability of the system. Spectroscopic data spanning the recent phase change narrows down the final changeover from emission to absorption to a period of about 6 months, and suggests that the Balmer emission faded gradually over a period in excess of 700 d. We discuss the similarity between this event and a previous extended low state seen in 1974-1977, where the star was again very faint, almost nonvariable and had no near-IR excess. We propose that this was another disk-loss or near disk-loss event. Previously unpublished X-ray data from the Ariel 5 satellite are presented which show a steady decrease in the 2-10 keV flux of the system, which persists well beyond the end of this earlier extended low phase. It would thus appear that there is no relation between the optical and X-ray lightcurve after the 1974-1977 low.