Stellar wind yields of very massive stars

The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMSs, M > 100 M-circle dot) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-b urning. VMS ha ve optically thick winds with ele v ated mass-loss rates in comparison to optically thin standard O-star winds. We compute wind yields and ejected masses on the main sequence, and we compare enhanced mass-loss rates to standard ones. We calculate solar metallicity wind yields from MESA stellar evolution models in the range 50-500 M-circle dot , including a large nuclear network of 92 isotopes, investigating not only the CNO-cycle, but also the Ne-Na and Mg-Al cycles. VMS with enhanced winds eject 5-10 times more H-processed elements (N, Ne, Na, Al) on the main sequence in comparison to standard winds, with possible consequences for observed anticorrelations, such as C-N and Na-O, in globular clusters. We find that for VMS 95 per cent of the total wind yields is produced on the main sequence, while only similar to 5 per cent is supplied by the post-main sequence. This implies that VMS with enhanced winds are the primary source of Al-26, contrasting previous works where classical Wolf-Rayet winds had been suggested to be responsible for galactic Al-26 enrichment. Finally, 200 M-circle dot stars eject 100 times more of each heavy element in their winds than 50 M-circle dot stars, and even when weighted by an IMF their wind contribution is still an order of magnitude higher than that of 50 M-circle dot stars.