Macroclumping as solution of the discrepancy between different mass loss diagnostics for O-type stars

Brankica Šurlan (Astronomický ústav Ondřejov)

Recent studies of O-type stars demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed - fitting the unsaturated UV resonance lines (e.g. P v) gives drastically lower values than obtained from the H_alpha emission. In this talk I will show that wind inhomogeneities (i.e. clumping) may resolve the reported discrepancy between H_alpha and P v mass loss diagnostics. For this purpose we select five O-type supergiants, from O4 to O7. The observed spectra in optical and UV regions are analysed with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres and with our 3-D Monte-Carlo code, which can account for wind clumps of any optical depths, a non-void inter-clump medium, and a velocity dispersion inside the clumps. Our results show that with the mass-loss rates that fit H_alpha (and other Balmer and He II lines), and the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced without problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates, nor to assume a sub-solar phosphorus abundance or an extremely high clumping factor, contrary to what was claimed by other authors.

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