THE SMALL-MAGELLANIC-CLOUD, SUPERSOFT X-RAY BINARY 1E-0035.4-7230 (SMC-13)

Details of simultaneous photometric and spectroscopic observations of the optical counterpart of the ''supersoft'' X-ray source in the Small Magellanic Cloud, 1E 0035.4-7230 (SMC 13), are presented. Although th e spectrum is dominated by emission lines of He II, the Balmer series of hydrogen is also present in emission with a strong decrement, and B almer lines are seen as broad absorptions. Several high-ionization emi ssion features are also present, including O VI (at 3811, 3834, and 52 90 Angstrom). Radial velocities and photometry confirm that the binary period is similar to 0(d).1719, and an improved value of the period i s derived from 4 years of photometry and analysis of ROSAT HRI X-ray d ata. The orbital light variation is primarily due to an eclipse of the extensive accretion disk. X-ray and optical minima occur together. Th e UBV light curves are similar to each other, and no clear phase-relat ed color variations are found. He II emission-line velocities show a s emiamplitude of K similar to 100 km s(-1), and maximum velocity occurs when the light curve indicates that the compact star would be moving away from the observer, suggesting that this emitting region may trace the orbital motion of the compact star. The range of possible masses implied for the X-ray source lies between 0.5 and 1.5 M-. if the mass donor is a main-sequence star filling its Roche lobe. The light curve suggests values at the high end of this range. The broad H absorption lines appear to have a much larger velocity amplitude and a lower syst emic velocity, making it difficult to understand their origin. We disc uss possible models for the system.