The Outer Envelope of the Wolf-Rayet Star $\gamma ^{2}$ Velorem

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Session 67 -- Compact Objects/Stellar Winds
Oral presentation, Thursday, 2, 1994, 10:00-11:30

[67.05] The Outer Envelope of the Wolf-Rayet Star $\gamma ^{2}$ Velorem

David E. Hogg (National Radio Astronomy Observatory)

Radio emission from the WC 8 Wolf-Rayet star $\gamma ^{2}$ Vel has been observed with the Very Large Array at five frequencies between 1.4 GHz and 22.4 GHz. The extended envelope is resolved at all wavelengths. The visibility function (cf. White and Becker 1982, ApJ, 262,657) is approximately that expected for an isothermal wind of constant velocity and mass loss rate. For this simple model the inferred temperature is 6000~K, and the mass loss rate, assuming the helium is mainly twice-ionized, is $8 \times 10 ^{-5} M_{\sun}$ $yr^{-1}$. The latter quantity is sensitively dependent on the ionization state of helium, which provides most of the electrons in the wind.

However, the visibility functions do deviate from the expected curves at both the short and the long baselines. Moreover, the spectral index of the total flux density for this range of wavelengths is 0.65, somewhat steeper than the value 0.60 expected from the simple model, and the halfwidths of the visibility functions, which are closely related to the effective size of the envelope and temperature of the wind, increase with frequency much more slowly than expected. The differences in visibility function and in the variation of size and flux density with frequency are used to explore the temperature and density of the extended envelope at distances between $4 \times 10^{14}$ cm and $2.5 \times 10^{15}$ cm from the central star.

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