Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...18912015c&link_type=abstract
American Astronomical Society, 189th AAS Meeting, late abstracts, #120.15; Bulletin of the American Astronomical, Vol. 29, p. 73
Astronomy and Astrophysics
Astronomy
Scientific paper
Since about 10 years ago it has been known that early-type stars can have time-variable, strong non-thermal emission of poorly understood origin. In 1994 and 1995 we have carried out multifrequency radio continuum VLA observations of a sample of 8 WR and O stars. We present here the main results of these observing runs: 1) The observed stars can be classified in 3 groups: a) Sources with a classic thermal wind, b) Sources which show clear non-thermal emission, c) Thermal sources with positive spectral index that differs from the classic 0.6 value. 2) We have derived mass loss rate values or upper limits for all objects. 3) From this sample we have found two objects that present interesting properties: the radio binary system Cyg OB2 No.5, whose radio companion (probably a third component) presents a strong non-thermal spectral index of -2.4, and WR 147 which shows a spectral index of 0.34 (suggesting an anisotropic wind). This last star also has a non-thermal companion. For both sources it is possible that the interaction between stellar winds is responsible for the observed non-thermal emission. In addition, recently it has become evident that these winds, in particular those of WR stars, can be anisotropic and inhomogeneous. WR 147 is a possible example of a star with these wind properties since both MERLIN and VLA maps show a markedly anisotropic wind with part of the emission coming from clumps. These condensations could have two possible origins: they are real inhomogeneities that are being carried by the wind or they are stationary shocks (or some wave phenomena) in the wind. We expect to present new observations taken during December 1996 and January 1997.
Contreras Espinoza M.
Rodriguez Luis F.
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