The optical light curve of 4U 1915 - 05

The optical counterpart of the X-ray-burst source 4U 1915 - 05 was observed photometrically on five nights in May and June 1987. The most likely period of the light curve is 48.746 + or - 0.035 min, although an alias at 50.458 + or - 0.037 min cannot be excluded. The largest scatter in the curve occurs between phases 0.7 and 0.1 and possibly represents azimuthal variations of an accretion disk, as seen in other LMXBs. There is evidence, however, that a portion of the scatter arises from a systematically changing depth of minimum light. This variation may be caused by precession of a tilted disk on a timescale of days. From the observed reddening of stars in the direction of 4U 1915 - 05, an intrinsic color of (B - V)o = -0.25 + or - 0.3 is derived for the system. At the distance implied by X-ray-burst luminosities, the disk in 4U 1915 - 05 has M(v) about + 3.3 + or - 0.9 at maximum light, which is significantly fainter than the disks in longer-period LMXBs.