Optical counterpart of the X-ray transient RX J0117.6-7330: Spectroscopy and photometry

We conducted spectroscopic and photometric observations of the optical comp anion of the X-ray transient RX J0117.6-7330 in the Small Magellanic Cloud, during a quiescent state. The primary star is identified as a B0.5 IIIe wi th a mass M* = (18 +/- 2)M. and bolometric magnitude M-bol = -7.4 +/- 0.2. The main spectral features are strong H alpha emission, H beta and H gamma emission cores with absorption wings, and narrow He I and O II absorption l ines. Equivalent widths and full widths at half maximum of the main lines a re listed. The average systemic velocity over our observing run is upsilon( r) = (184 +/- 4) km s(-1); measurements over a longer period of time are ne eded to determine the binary period and the K velocity of the primary. We d etermine a projected rotational velocity upsilon sin i = (145 +/- 10) km s( -1) for the Be star; if we assume a true rotational velocity at the equator upsilon = (400 +/- 50) km s(-1), we deduce that the inclination angle of t he system is i = (21 +/- 3) deg.