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The VLT-FLAMES Tarantula Survey XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus | | O.H. Ramírez-Agudelo
; H. Sana
; A. de Koter
; F. Tramper
; N.J. Grin
; F.R.N. Schneider
; N. Langer
; J. Puls
; N. Markova
; J.M. Bestenlehner
; N. Castro
; P.A. Crowther
; C.J. Evans
; M. García
; G. Gräfener
; A. Herrero
; B. van Kempen
; D.J. Lennon
; J. Maíz Apellániz
; F. Najarro
; C. Sabín-Sanjulián
; S. Simón-Díaz
; W.D. Taylor
; J.S. Vink
; | | Date: |
17 Jan 2017 | | Abstract: | The Tarantula region in the Large Magellanic Cloud contains the richest
population of spatially resolved massive O-type stars known so far. This
unmatched sample offers an opportunity to test models describing their
main-sequence evolution and mass-loss properties. Using ground-based optical
spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey
(VFTS), we aim to determine stellar, photospheric and wind properties of 72
presumably single O-type giants, bright giants and supergiants and to confront
them with predictions of stellar evolution and of line-driven mass-loss
theories. We apply an automated method for quantitative spectroscopic analysis
of O stars combining the non-LTE stellar atmosphere model {{sc fastwind}} with
the genetic fitting algorithm {{sc pikaia}} to determine the following stellar
properties: effective temperature, surface gravity, mass-loss rate, helium
abundance, and projected rotational velocity. We present empirical effective
temperature versus spectral subtype calibrations at LMC-metallicity for giants
and supergiants. In the spectroscopic and classical Hertzsprung-Russell
diagrams, our sample O stars are found to occupy the region predicted to be the
core hydrogen-burning phase by Brott et al. (2011) and K"{o}hler et al.
(2015). Except for five stars, the helium abundance of our sample stars is in
agreement with the initial LMC composition. The aforementioned five stars
present moderate projected rotational velocities (i.e.,
$v_{mathrm{e}},sin,i,<,200,mathrm{km,s^{-1}}$) and hence do not agree
with current predictions of rotational mixing in main-sequence stars. Adopting
theoretical results for the wind velocity law, we find modified wind momenta
for LMC stars that are $sim$0.3 dex higher than earlier results. [Due to the
limitation of characters, the abstract appearing here is slightly shorter than
that in the PDF file.] | | Source: | arXiv, 1701.4758 | | Services: | Forum | Review | PDF | Favorites | |
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