Sabín-Sanjulián, C.; Simón-Díaz, S.; Herrero, A.; Puls, J.; Schneider, F. R. N.; Evans, C. J.; Garcia, M.; Najarro, F.; Brott, I.; Castro, N.; Crowther, P. A.; de Koter, A.; de Mink, S. E.; Gräfener, G.; Grin, N. J.; Holgado, G.; Langer, N.; Lennon, D. J.; Maíz Apellániz, J.; Ramírez-Agudelo, O. H.; Sana, H.; Taylor, W. D.; Vink, J. S.; Walborn, N. R.
Bibliographical reference
Astronomy and Astrophysics, Volume 601, id.A79, 22 pp.
Advertised on:
5
2017
Journal
Citations
46
Refereed citations
43
Description
Context. The VLT-FLAMES Tarantula Survey has observed hundreds of O-type
stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). Aims: We study the properties of a statistically significant sample
of O-type dwarfs in the same star-forming region and test the latest
atmospheric and evolutionary models of the early main-sequence phase of
massive stars. Methods: We performed quantitative spectroscopic
analysis of 105 apparently single O-type dwarfs. To determine stellar
and wind parameters, we used the iacob-gbat package, an automatic
procedure based on a large grid of atmospheric models that are
calculated with the fastwind code. This package was developed for the
analysis of optical spectra of O-type stars. In addition to classical
techniques, we applied the Bayesian bonnsai tool to estimate
evolutionary masses. Results: We provide a new calibration of
effective temperature vs. spectral type for O-type dwarfs in the LMC,
based on our homogeneous analysis of the largest sample of such objects
to date and including all spectral subtypes. Good agreement with
previous results is found, although the sampling at the earliest
subtypes could be improved. Rotation rates and helium abundances are
studied in an evolutionary context. We find that most of the rapid
rotators (v sin i > 300 km s-1) in our sample have masses
below 25 M⊙ and intermediate rotation-corrected
gravities (3.9 < log gc < 4.1). Such rapid rotators are
scarce at higher gravities (i.e. younger ages) and absent at lower
gravities (larger ages). This is not expected from theoretical
evolutionary models, and does not appear to be due to a selection bias
in our sample. We compare the estimated evolutionary and spectroscopic
masses, finding a trend that the former is higher for masses below 20
M⊙. This can be explained as a consequence of limiting
our sample to the O-type stars, and we see no compelling evidence for a
systematic mass discrepancy. For most of the stars in the sample we were
unable to estimate the wind-strength parameter (hence mass-loss rates)
reliably, particularly for objects with lower luminosity (log
L/L⊙ ≲ 5.1). Only with ultraviolet spectroscopy will
we be able to undertake a detailed investigation of the wind properties
of these dwarfs.
Based on observations at the European Southern Observatory Very Large
Telescope in program 182.D-0222.Tables A.1 to B.2 are also available at
the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A79
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