A model for the radio-continuum emission from the P Cygni wind

¹ Centro de Radioastronomía y Astrofísica, UNAM, Morelia Mich., México e-mail: rf.gonzalez@astrosmo.unam.mx
² Instituto de Astronomía, UNAM , México D.F., México

Received: 6 March 2007
Accepted: 6 November 2007

Abstract

Here we present a simple, semianalytic model for estimating the free-free radiation (at radio wavelengths) from the P Cygni stellar wind. Recent observations from this source at different epochs show time-dependent flux densities and spectral indices, which clearly deviate from the standard models of ionized extended envelopes around massive stars. In this work, we study the contribution by shocks to the total emission from a completely ionized stellar wind, which results from variations in the wind parameters at injection. In particular, we consider sudden changes in the wind velocity and mass loss rate that instantaneously produce two-shock wave structures (called working surfaces) that travel down the flow. The compressed layer between the two shocks emits continuum radiation that can be detected in the radio band. We show that our model gives a possible explanation for the observed variability in the flux densities and spectral indices from the P Cygni wind.