Bibcode
Bestenlehner, J. M.; Gräfener, G.; Vink, J. S.; Najarro, F.; de Koter, A.; Sana, H.; Evans, C. J.; Crowther, P. A.; Hénault-Brunet, V.; Herrero, A.; Langer, N.; Schneider, F. R. N.; Simón-Díaz, S.; Taylor, W. D.; Walborn, N. R.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 570, id.A38, 92 pp.
Fecha de publicación:
10
2014
Revista
Número de citas
132
Número de citas referidas
112
Descripción
The evolution and fate of very massive stars (VMS) is tightly connected
to their mass-loss properties. Their initial and final masses differ
significantly as a result of mass loss. VMS have strong stellar winds
and extremely high ionising fluxes, which are thought to be critical
sources of both mechanical and radiative feedback in giant H ii regions.
However, how VMS mass-loss properties change during stellar evolution is
poorly understood. In the framework of the VLT-Flames Tarantula Survey
(VFTS), we explore the mass-loss transition region from optically thin O
star winds to denser WNh Wolf-Rayet star winds, thereby testing
theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and
WNh stars, an unprecedented sample of stars with the highest masses and
luminosities known. We perform a spectral analysis of optical VFTS as
well as near-infrared VLT/SINFONI data using the non-LTE radiative
transfer code CMFGEN to obtain both stellar and wind parameters. For the
first time, we observationally resolve the transition between optically
thin O star winds and optically thick hydrogen-rich WNh Wolf-Rayet
winds. Our results suggest the existence of a "kink" between both
mass-loss regimes, in agreement with recent Monte Carlo simulations. For
the optically thick regime, we confirm the steep dependence on the
classical Eddington factor Γe from previous theoretical
and observational studies. The transition occurs on the main sequence
near a luminosity of 106.1L⊙, or a mass of 80
... 90 M⊙. Above this limit, we find that - even when
accounting for moderate wind clumping (with fv = 0.1) - wind
mass-loss rates are enhanced with respect to standard prescriptions
currently adopted in stellar evolution calculations. We also show that
this results in substantial helium surface enrichment. Finally, based on
our spectroscopic analyses, we are able to provide the most accurate
ionising fluxes for VMS known to date, confirming the pivotal role of
VMS in ionising and shaping their environments.
Appendices are available in electronic form at http://www.aanda.org
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