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Session 44 - Double Stars.
Display session, Thursday, January 08
We present results of a \approx30 ksec ASCA X-ray observation of the unusual Wolf-Rayet star AS431 (= WR147). Infrared observations have revealed a 2.2 micron source located \approx0.''6 north of the optical WN8 star, which is possibly a companion. Nonthermal radio emission has been detected at a position nearly coincident with the IR source, but its origin is not yet understood. Our objective was to place tighter constraints on the origin of the X-ray emission that was originally detected by Einstein, with emphasis on discriminating between wind shock models and models that postulate accretion onto a compact companion. The ASCA spectra cover the energy range 0.5 - 10 keV, but are heavily absorbed below \sim1 keV with a derived column density of N_H \approx 10^22.3 cm^-2. Roughly half of the observed flux emerges at energies above 4 keV. Emission lines are present, and spectral models show a strong contribution from plasma over a broad range of temperatures from \leq0.4 keV up to at least \approx2 keV. No X-ray variability was detected down to a time resolution of 512 s. The absorption-corrected X-ray lumimosity is L_x (0.5 - 10 keV) = 6 \times 10^32 ergs s^-1 at a distance of 630 pc. We will discuss these new X-ray results in the context of wind shock and compact companion models.
Program listing for Thursday