PHASE-RESOLVED OPTICAL PHOTOMETRY AND SPECTROSCOPY OF THE SUPERSOFT X-RAY BINARY 1E-0035.4-7230

We present phase-resolved optical photometry and spectroscopy of the s upersoft X-ray binary 1E 0035.4-7230 (= SMC 13). The average U, B, V, and R light curves show an almost perfect sinusoidal Delta m similar t o 0.3 mag modulation on the 4.1 hr orbital period, but in individual b inary orbits there can be significant deviations from the average ligh t curves. There is a significant B - V variability with a standard dev iation of 0.04 mag, and which may be related to the orbital phase. The binary appears to be bluest similar to 0.2 - 0.3 in orbital phase bef ore optical minimum. Modeling of the light curves indicates an orbital inclination of similar to 20 - 50 degrees and a mass ratio M-1/M-2 < 3 (with M-1 the mass of the accreting star). The observed optical modu lation is probably dominated by the changing aspect of the irradiated companion star, which has effective temperatures on the irradiated sid e greater than or similar to 30000 K. Our spectra show variable He II lambda 4686 emission, and broad Balmer absorption lines. The latter ap pear more prominent when the companion star is closest to us. Modeling the optical spectrum of the irradiated companion star by a compositio n of normal stellar spectra reproduces the observed colour and amplitu de of the modulation, but predicts too strong Balmer absorption lines which must be significantly weaker because of strong irradiation.