ζ Oph and the weak-wind problem

Abstract

Mass-loss rate, ̇ M, is one of the key parameters affecting evolution and observational manifestations of massive stars and their impact on the ambient medium. Despite its importance, there is a factor of ~100 discrepancy between empirical and theoretical ̇ M of late-type O dwarfs, the so-called weak-wind problem. In this Letter, we propose a simple novel method to constrain ̇ M of runaway massive stars through observation of their bow shocks and Str̈omgren spheres, which might be of decisive importance for resolving the weak-wind problem. Using this method, we found that ̇ M of the well-known runaway O9.5V star ζ Oph is more than an order of magnitude higher than that derived from ultraviolet (UV) line fitting and is by a factor of 6-7 lower than those based on the theoretical recipe by Vink et al. and the Hα line. The discrepancy between ̇ M derived by our method and that based on UV lines would be even more severe if the stellar wind is clumpy. At the same time, our estimate of ̇ M agrees with that predicted by the moving reversing layer theory by Lucy. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.