The Optical Counterpart of the X-ray Transient RX J0117.6-7330: Spectroscopy and Photometry

Abstract

We conducted spectroscopic and photometric observations of the optical counterpart 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, with mass M = (18 +/- 2) M(sun) 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 HeI and OII absorption lines. Equivalent width and FWHM of the main lines are listed. The average systemic velocity over our observing run is v(r) = (184 +/- 4) km/s; measurements over a longer period of time are needed to determine the binary period and the K velocity of the primary. We determine a projected rotational velocity v sin i = (145 +/- 10) km/s for the Be star, and we deduce that the inclination angle of the system is i = (21 +/- 3)deg.