Mass loss and the Eddington parameter: a new mass-loss recipe for hot and massive stars
Abstract
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 (> 100 M_{⊙}) are highly uncertain. Such stars display Wolf-Rayet spectral morphologies (WNh), whilst on the main sequence. Metal-poor very massive stars 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 (Γe). 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} ∝ Γ _e3, while in the optically thick wind regime \dot{M} ∝ 1/ (1 - Γ _e)^{3.5}. The transition from optically thin to optically thick winds occurs at Γe, trans ≈ 0.47. The transition mass-loss rate is log \dot{M}~(M_{⊙ } yr^{-1}) ≈ -4.76 ± 0.18, which is in line with the prediction by Vink & Gräfener assuming a volume filling factor of f_V = 0.23_{-0.15}^{+0.40}.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2020
- DOI:
- 10.1093/mnras/staa474
- arXiv:
- arXiv:2002.05168
- Bibcode:
- 2020MNRAS.493.3938B
- Keywords:
-
- stars: atmospheres;
- stars: early-type;
- stars: mass-loss;
- stars: winds;
- outflows;
- stars: Wolf-Rayet;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted for publication in MNRAS, 9 pages, 5 figures