ROSAT X-RAY OBSERVATIONS OF THE WR-STARS HD-50896 (WN5) AND GAMMA-VELORUM (WC8+O9I)

We present a preliminary analysis of multiple X-ray (0.1-2.5 keV) obse rvations of HD 50896 and gamma Velorum obtained with the ROSAT satelli te. For HD 50896, our 8 observations show variability at the 30% level on timescales of similar to 1 day, together with larger (x 1.7) epoch -changes, but no evidence for rapid variability. No phase-dependent mo dulation is apparent on the 3d.766 optical period. The mean PSPC spect rum gives kT = 0.28 keV, log N(H) = 20.6, and L(x) = 3.8 x 10(32) erg s(-1), and implies that the observed X-rays have undergone little abso rption in the WN5 wind. For gamma Velorum, we have 13 observations sec ured over several cycles in the 78d.5 binary period. At most binary ph ases, the X-ray emission is relatively constant, with kT similar or eq ual to 0.19 keV, log N(H) = 20.2, and L(x) = 2.5 x 10(31) s(-1) Near o rbital phase 0.5, the X-erg ray emission is enhanced by a factor of 4, due almost entirely to an additional harder component with kT greater than or equal to 2 keV. We believe this is due to X-ray emission prod uced in the collision of the two stellar winds.