Time‐ResolvedFUSESpectroscopy of the LMC WC + O Binaries Br 22 and Br 32

Abstract

Using the Far Ultraviolet Spectroscopic Explorer satellite, we obtained series of spectra for two of the three known WC + O binaries in the LMC, Br 22, and Br 32 (HD 36521). Compared to Br 22, we detect a higher ratio of C IV to He II lines in Br 32, which could indicate a more advanced evolutionary stage for the latter. The orbit of the O star in Br 32 has been determined from its P V absorption lines. We find that continuum fluxes in both systems are substantially diluted by a third-light source. The maximum extension of the black absorption troughs in P Cygni profiles provides the terminal velocities of the WC winds: 3775 ± 125 km s−1 for Br 22 and 4400 ± 150 km s−1 for Br 32. From the phase-dependent displacements of the blue absorption edges of prominent emission lines we estimate the half-opening angles of the wind-wind collision zones and their Coriolis deflections. In both binaries we fitted, via iterative procedure, the phase-dependent changes in the O VI λ1032-1037 and C III λ1175 profiles as a function of the wind, stellar, and orbital parameters. This allowed us to isolate the excess emission produced in the wind-wind collision zone and reproduce profile changes caused by atmospheric eclipses. A strong extra emission component is observed in Br 22 (P = 14.9 days), while it is negligible in Br 32 (P = 1.9 days).