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Session 77 - Binary Stars.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[77.17] ASCA Observations of the Unusual Wolf-Rayet Star HD50896 (= EZ CMa)

S. Skinner (JILA/U. Colorado), F. Nagase, H. Ozawa (ISAS), M. Itoh (Kobe U.)

We present initial results from a 30 ksec ASCA X-ray observation of the unusual WN5 Wolf-Rayet star HD50896 (= EZ CMa). This star has a well-documented (but poorly understood) optical period of 3.766 d and is a candidate WR + neutron star binary system. The ASCA observation reveals a prominent X-ray source with an observed (absorbed) flux of 1.1 \times 10^-12 ergs cm^-2 s^-1 (0.5 - 10 keV), corresponding to a luminosity L_x = 4.3 \times 10^32 ergs s^-1 at a distance of 1.8 kpc. The X-ray light curve shows no significant variability during the \approx21 hours spanning the observation, down to a sensitivity-limited time resolution of \approx512 s. Spectra from the solid-state imaging spectrometers (SIS) show prominent emission lines from Si and S, implying a thermal emission mechanism. Acceptable fits with an optically thin plasma model require a cool component at kT \approx 0.6 keV (\approx7 MK) viewed through a modest absorption column N_H = 4 \times 10^20 cm^-2 and an additional hotter component viewed through heavier absorption. We discuss these new ASCA data in the context of various emission models including wind shocks and accretion onto a neutron star companion.

Program listing for Wednesday