Optical spectroscopy of X-Mega targets - I. CPD-59 degrees 2635: a new double-lined O-type binary in the Carina Nebula

Optical spectroscopy of CPD -59 degrees 2635, one of the O-type stars in th e open cluster Trumpler 16 in the Carina Nebula, reveals this star to be a double-lined binary system. We have obtained the first radial velocity orbi t for this system, consisting of a circular solution with a period of 2.299 9 d and semi-amplitudes of 208 and 273 km s(-1). This results in minimum ma sses of 15 and 11 M-. for the binary components of CPD -59 degrees 2635, wh ich we classified as O8V and O9.5V, although spectral type variations of th e order of I subclass, which we identify as the Struve-Sahade effect, seem to be present in both components. From ROSAT HRI observations of CPD -59 de grees 2635 we determine a luminosity ratio log(L-x/L-bol) approximate to -7 , which is similar to that observed for other O-type stars in the Carina Ne bula region. No evidence of light variations is present in the available op tical or X-ray data sets.