A SUPERSOFT X-RAY BINARY IN THE SMALL MAGELLANIC CLOUD

Photometric observations of the supersoft x-ray source 1E 0035.4-7230 obtained during two years reveal that the very blue optical counterpar t (V-max=20.2, B-V=-0,15, U-B=-1.06) undergoes nearly sinusoidal varia tions with a period of 0.1719256 days and an amplitude of Delta V simi lar to 0.3 mag. ROSAT observations show the x rays vary with approxima tely the same period. However, either the x-ray minimum precedes the o ptical minimum by about a quarter cycle or there is a small period dif ference between the two wavelength regions. We consider that this x-ra y source is a close binary, with the optical light coming primarily fr om an accretion disk surrounding the compact star. Optical spectra sho w weak, variable He II (4686 Angstrom) emission which probably origina tes in this disk. Possible interpretations of the light curve are disc ussed, including x-ray heating of the secondary star. The very broad m inimum in the x-ray light curve suggests the x rays may be scattered i n a large accretion disk corona (ADC) which is partially occulted, pro bably by an azimuthally irregular bulge on the disk rim. If this syste m lies at the distance of the Small Magellanic Cloud, it radiates near the Eddington luminosity. (C) 1996 American Astronomical Society.