C.D.S. - SIMBAD4 rel 1.7 - 2020.07.13CEST01:09:36

2011A&A...531A.132V - Astronomy and Astrophysics, volume 531A, 132-132 (2011/7-1)

Wind modelling of very massive stars up to 300 solar masses.


Abstract (from CDS):

The stellar upper-mass limit is highly uncertain. Some studies have claimed there is a universal upper limit of ∼150M. A factor that is often overlooked is that there might be a significant difference between the present-day and the initial masses of the most massive stars - as a result of mass loss. The upper-mass limit may easily supersede ∼200M. For these reasons, we present new mass-loss predictions from Monte Carlo radiative transfer models for very massive stars (VMS) in the mass range 40-300 M, and with very high luminosities 6.0≤log(L*/L)≤7.03, corresponding to large Eddington factors Γ. Using our new dynamical approach, we find an upturn or ``kink'' in the mass-loss versus Γ dependence, at the point where the model winds become optically thick. This coincides with the location where our wind efficiency numbers surpass the single-scattering limit of η=1, reaching values up to η≃2.5. In all, our modelling suggests a transition from common O-type winds to Wolf-Rayet characteristics at the point where the winds become optically thick. This transitional behaviour is also revealed with respect to the wind acceleration parameter, β, which starts at values below 1 for the optically thin O-stars, and naturally reaches values as high as 1.5-2 for the optically thick Wolf-Rayet models. An additional finding concerns the transition in spectral morphology of the Of and WN characteristic He ii line at 4686Å. When we express our mass-loss predictions as a function of the electron scattering Eddington factor Γe∼L*/M* alone, we obtain an {dot}(M) vs. Γe dependence that is consistent with a previously reported power law {dot}(M) ∝ Γe5 (Vink 2006, ASPC, 353, 113) that was based on our previous semi-empirical modelling approach. When we express {dot}(M) in terms of both Γe and stellar mass, we find optically thin winds and {dot}(M) ∝ M*0.68 Γe2.2 for the Γe range 0.4≲Γe≲0.7, and mass-loss rates that agree with the standard Vink et al. (2000A&A...362..295V) recipe for normal O stars. For higher Γe values, the winds are optically thick and, as pointed out, the dependence is much steeper, {dot}(M)∝M*0.78Γe4.77. Finally, we confirm that the effect of Γ on the predicted mass-loss rates is much stronger than for the increased helium abundance, calling for a fundamental revision in the way stellar mass loss is incorporated in evolutionary models for the most massive stars.

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Journal keyword(s): stars: massive - supergiants - stars: winds, outflows - stars: Wolf-Rayet - stars: mass-loss

Simbad objects: 2

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Number of rows : 2

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
1 * eta Car Em* 10 45 03.5455050 -59 41 03.951060 6.37 7.034 6.21 4.90 4.41 OBepec 2201 0
2 NAME Arches Cluster Cl* 17 45 50.5 -28 49 28           ~ 630 0

    Equat.    Gal    SGal    Ecl

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