On the intensity and shape of radio recombination lines from ionized stellar winds

The ionized wind of early-type stars emit continuum (free-free) radiation that has been detected in the radio frequencies for an appreciable number of stars. The measurement of this continuum emission allows a reliable determination of the ratio of mass-loss rate to wind terminal velocity; M/Vsub(infinity). These winds should also emit very weak and wide radio recombination lines. The detection of these lines would allow a determination of Vsub(infinity) and M separately. We calculate the expected intensity and shape of these lines. For typical winds the lines are too weak and wide to be detected with presently available instruments. However, stellar winds with peculiarly low terminal velocities may have detectable radio recombination line emission. In particular, lines have been detected recently in MWC349. We discuss the line characteristics of this source. (author)