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

Abstract

AbstractWe conducted spectroscopic and photometric observations of the optical companion 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 a mass M* = (18 ± 2)M⨀ and bolometric magnitude Mbol = –7·4 ± 0·2. The main spectral features are strong Hα emission, Hβ and Hγ emission cores with absorption wings, and narrow He I and O II absorption lines. Equivalent widths and full widths at half maximum of the main lines are listed. The average systemic velocity over our observing run is vr = (184 ± 4) km s−1; 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−1 for the Be star; if we assume a true rotational velocity at the equator v = (400 ± 50) km s−1, we deduce that the inclination angle of the system is i = (21 ± 3) deg.