Simultaneous Photometry of X Persei and 3U 0352 + 30

Abstract

The suggested association of X Persei with the weak X-ray source 3U 0352 + 30 raises the possibility of detection of X-ray/optical covariability. We have successfully conducted a simultaneous optical/X-ray observation utilizing groundbased photometry and a satellite-borne proportional counter. Photoelectric photometry of X Persei was obtained on five out of seven consecutive nights in 1975 January, from the Lick and Leuschner Observatories. The observations yield $$B\,=\,6\cdot848\pm0\cdot002,\,B-V\,=\,0\cdot139\pm0\cdot001$$, with no strong evidence for variability during the observing run. These are the faintest and bluest photoelectric magnitudes and colours ever reported for X Per; this change apparently occurred relatively uniformly during 1973–74 and is reminiscent of behaviour last observed in about 1900. On January 21, 7 hr of data were obtained from both observatories simultaneously with OAO Copernicus X-ray observations of 3U 0352 + 30. The X-ray flux varied during this period by a factor of 2, but there is no obviously correspondent optical activity, to a level of 0·02 mag. The optical data are also used to limit to 0·01-mag variations coincident with the X-ray periodicity reported by White et al.