Spectroscopic studies of Wolf-Rayet stars with absorption lines. I - The probable single WN5 star HD 193077

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Abstract
The WN5 Wolf-Rayet star HD 193077 has been called a binary because of the presence of absorption lines in its spectrum. I have studied this star at high dispersion and can set an upper limit on the orbital semiamplitude of 30 km s-1 for the emission lines and 80 km s-1 for the absorption lines, for periods less than 6 months. There is no evidence of velocity variations greater than this amount during the past 15 years. The absorption lines are rotationally broadened to 500 km s-1 (greater than that of any known early-type star), but have strengths normal for an 0 star. If these lines originate in an OB companion, then this high rotation velocity, combined with the limits on the velocity variations, sets very stringent limits on the allowed orbital inclinations and periods. Furthermore, there is evidence of hydrogen in the emission-producing envelope, with N(H)IN(He) ̃0.8, as large as that known for any early WN star. Taken together, these observations suggest that the absorption lines are intrinsic to the W-R star itself, and that HD 193077 is a newly arrived, single Wolf-Rayet star, although the possibility that it is a binary system with a highly eccentric orbit or extremely long period cannot be completely excluded.

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