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Paper: Mass Loss in Massive Stars
Volume: 332, The Fate of the Most Massive Stars
Page: 215
Authors: Hillier, D.J.
Abstract: We discuss the recent revision to the effective temperature scale of O stars. The new temperature scale is cooler by 1000K to > 4000 K. The revision has arisen from the use of more accurate atmospheric models which allow for non-LTE line blanketing and stellar winds. We review quiescent mass loss in massive stars, highlighting some of the uncertainties in our current understanding. There is generally good agreement between observed mass-loss rates and those predicted using radiation driven wind theory. In particular, the general scaling of mass-loss rate with luminosity ( dM/dt ∝ L1.8) is clearly seen in the observations of O stars. However, as we have improved the accuracy of the spectroscopic analyses, it is apparent that we do not have a full understanding of mass loss in massive stars. There is strong evidence that stellar winds are highly clumped, and there are potentially discrepancies (factor of 2 to 5) between predicted and observed mass-loss rates. Further, there is some evidence that mass-loss rates in low luminosity O stars may be an order of magnitude lower than predicted. While some discrepancies could be due to the neglect of stellar rotation, improvements to the spectroscopic models and in our understanding of stellar winds in massive stars are needed. An analysis of two O7 stars, AV69 [OC7.5III((f))] and AV83 (O7 Iaf+), is used to highlight the role of rotation on surface abundances, and the evidence for wind clumping.
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