A NEW THEORETICAL CALIBRATION OF THE RELATION BETWEEN MASS-LOSS RATE AND H-ALPHA EMISSION FOR O-STAR WINDS

Luminosities of O star winds in H I Hα have been calculated from a series of wind ionization models based on the dynamical structure predicted by time-independent radiation-driven wind theory (Friend and Abbott; Pauldrach, Puls, and Kudritzki). The models span the entire range in effective temperature and luminosity falling within the O spectral class. A number of different velocity laws are considered. Best-fit relations involving L(Hα), Ṁ, υ∞, and the stellar radius, R, are obtained for each velocity law. Mass-loss rates obtained from observed values of L(Hα) using the new fits are compared with mass-loss rates for the same stars derived from radio flux measurements. The former are found to be, on average, about 2 times larger than the latter when the theoretically preferred β = 0.7 velocity law is assumed. Better agreement is achieved when a much more slowly accelerating β = 1.5 velocity law is used instead. Confirmation of this is obtained in a separate comparison with mass-loss rates derived semiempirically from H I Hα by Leitherer. It is suggested that this result may be evidence of enhanced Hα emission from the inner, accelerating portion of these winds, where the onset of wind instability gives rise to density inhomogeneities.