The Wolf-Rayet Stellar Response To The Iron Opacity Bump: Envelope Inflation, Winds, and Microturbulence. (arXiv:1904.01703v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ro_S/0/1/0/all/0/1">Stephen Ro</a>
Early-type Wolf-Rayet(WR) stellar models harbor a super-Eddington layer in
their outer envelopes due to a prominent iron opacity bump. In the past few
decades, one-dimensional hydrostatic and time-steady hydrodynamic models have
suggested a variety of WR responses to a super-Eddington force including
envelope inflation and optically thick winds. In this paper, I study these
responses using semianalytical estimates and WR models from both MESA and Ro &
Matzner; four conclusions are present. First, early-type WR stars do not harbor
inflated envelopes because they have either strong winds or insufficient
luminosities. Second, the condition for an opacity bump to harbor a sonic point
is expressible as a minimum mass-loss rate, $dot{M}_{rm sp}(L_*)$. In
agreement with Grassitelli et al. and Ro, the majority of galactic early-type
WR stars can harbor sonic points at the iron opacity bump. However, about half
of those in the Large Magellanic Cloud cannot given typical wind parameters.
Third, WR winds driven by the iron opacity bump must have mass-loss rates that
exceed a global minimum of $10^{-5.8}-10^{-6}M_odot,{rm yr}^{-1}$. Lastly,
the observed early-type WR distribution follows a simple mass-loss relation
derived here if the radiation-to-gas pressure ratio is approximately $p_r/p_g
sim 145$ in the wind; a value consistent with studies by Grafener et al. and
Nakauchi & Saio.
Early-type Wolf-Rayet(WR) stellar models harbor a super-Eddington layer in
their outer envelopes due to a prominent iron opacity bump. In the past few
decades, one-dimensional hydrostatic and time-steady hydrodynamic models have
suggested a variety of WR responses to a super-Eddington force including
envelope inflation and optically thick winds. In this paper, I study these
responses using semianalytical estimates and WR models from both MESA and Ro &
Matzner; four conclusions are present. First, early-type WR stars do not harbor
inflated envelopes because they have either strong winds or insufficient
luminosities. Second, the condition for an opacity bump to harbor a sonic point
is expressible as a minimum mass-loss rate, $dot{M}_{rm sp}(L_*)$. In
agreement with Grassitelli et al. and Ro, the majority of galactic early-type
WR stars can harbor sonic points at the iron opacity bump. However, about half
of those in the Large Magellanic Cloud cannot given typical wind parameters.
Third, WR winds driven by the iron opacity bump must have mass-loss rates that
exceed a global minimum of $10^{-5.8}-10^{-6}M_odot,{rm yr}^{-1}$. Lastly,
the observed early-type WR distribution follows a simple mass-loss relation
derived here if the radiation-to-gas pressure ratio is approximately $p_r/p_g
sim 145$ in the wind; a value consistent with studies by Grafener et al. and
Nakauchi & Saio.
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