Mass loss and the Eddington parameter: a new mass-loss recipe for hot and massive stars. (arXiv:2002.05168v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bestenlehner_J/0/1/0/all/0/1">Joachim M. Bestenlehner</a>
Mass loss through stellar winds plays a dominant role in the evolution of
massive stars. In particular the mass-loss rates of very massive stars (VMSs,
$> 100,M_{odot}$) are highly uncertain. Such stars display Wolf-Rayet
spectral morphologies (WNh) whilst on the main-sequence. Metal-poor VMSs are
progenitors of gamma-ray bursts and pair instability supernovae. In this study
we extended the widely used stellar wind theory by Castor, Abbott & Klein from
the optically thin (O star) to the optically thick main-sequence (WNh) wind
regime. In particular we modify the mass-loss rate formula in a way that we are
able to explain the empirical mass-loss dependence on the Eddington parameter
($Gamma_{rm e}$). The new mass-loss recipe is suitable for incorporation into
current stellar evolution models for massive and very massive stars. It makes
verifiable predictions, namely how the mass-loss rate scales with metallicity
and at which Eddington parameter the transition from optically thin O star to
optically thick WNh star winds occurs. In the case of the star cluster R136 in
the Large Magellanic Cloud we find in the optically thin wind regime $dot{M}
propto Gamma_{rm e}^{3}$ while in the optically thick wind regime $dot{M}
propto 1/ (1 – Gamma_{rm e})^{3.5}$. The transition from optically thin to
optically thick winds occurs at $Gamma_{rm e, trans} approx 0.47$. The
transition mass-loss rate is $log dot{M}~(M_{odot} mathrm{yr}^{-1}) approx
-4.76 pm 0.18$, which is in line with the prediction by Vink & Gr”afener
assuming a volume filling factor of $f_{rm V} = 0.23_{-0.15}^{+0.40}$.
Mass loss through stellar winds plays a dominant role in the evolution of
massive stars. In particular the mass-loss rates of very massive stars (VMSs,
$> 100,M_{odot}$) are highly uncertain. Such stars display Wolf-Rayet
spectral morphologies (WNh) whilst on the main-sequence. Metal-poor VMSs are
progenitors of gamma-ray bursts and pair instability supernovae. In this study
we extended the widely used stellar wind theory by Castor, Abbott & Klein from
the optically thin (O star) to the optically thick main-sequence (WNh) wind
regime. In particular we modify the mass-loss rate formula in a way that we are
able to explain the empirical mass-loss dependence on the Eddington parameter
($Gamma_{rm e}$). The new mass-loss recipe is suitable for incorporation into
current stellar evolution models for massive and very massive stars. It makes
verifiable predictions, namely how the mass-loss rate scales with metallicity
and at which Eddington parameter the transition from optically thin O star to
optically thick WNh star winds occurs. In the case of the star cluster R136 in
the Large Magellanic Cloud we find in the optically thin wind regime $dot{M}
propto Gamma_{rm e}^{3}$ while in the optically thick wind regime $dot{M}
propto 1/ (1 – Gamma_{rm e})^{3.5}$. The transition from optically thin to
optically thick winds occurs at $Gamma_{rm e, trans} approx 0.47$. The
transition mass-loss rate is $log dot{M}~(M_{odot} mathrm{yr}^{-1}) approx
-4.76 pm 0.18$, which is in line with the prediction by Vink & Gr”afener
assuming a volume filling factor of $f_{rm V} = 0.23_{-0.15}^{+0.40}$.
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