Bibcode
Herrero, A.; Garcia, M.; Puls, J.; Uytterhoeven, K.; Najarro, F.; Lennon, D. J.; Rivero-González, J. G.
Bibliographical reference
Astronomy and Astrophysics, Volume 543, id.A85
Advertised on:
7
2012
Journal
Citations
29
Refereed citations
18
Description
Context. Results from the theory of radiatively driven winds are
nowadays incorporated in stellar evolutionary and population synthesis
models, and are used in our interpretation of the observations of the
deep Universe. Yet, the theory has been confirmed only until Small
Magellanic Cloud metallicities. Observations and analyses of O-stars at
lower metallicities are difficult, but much needed to prove the theory.
Aims: We have observed GHV-62024, an O6.5 IIIf star in the
low-metallicity galaxy IC 1613 (Z ≈ 0.15 Z&sun;) to study
its evolution and wind. According to a previous preliminary analysis
that was subject to significant restrictions this star could challenge
the radiatively driven wind theory at low metallicities. Here we present
a complete analysis of this star. Methods: Our observations were
obtained with VIMOS at VLT, at R ≈ 2000 and covered approximately
between 4000 and 7000 Å. The observations were analysed using the
latest version of the model atmosphere code FASTWIND, which includes the
possibility of calculating the N iii spectrum. Results: We obtain
the stellar parameters and conclude that the star follows the average
wind momentum-luminosity relationship (WLR) expected for its
metallicity, but with a high value for the exponent of the wind velocity
law, β. Comparing this with values of other stars in the
literature, we suggest that this high value may be reached because
GHV-62024 could be a fast rotator seen at a low inclination angle. We
also suggest that this could favour the appearance of the spectral
"f"-characterictics. While the derived β value does not change by
adopting a lower wind terminal velocity, we show that a wrong
V∞ has a clear impact on the position of the star in
the WLR diagram. The N and He abundances are very high, consistent with
strong CNO mixing that could have been caused by the fast rotation,
although we cannot discard a different origin with present data. Stellar
evolutionary model predictions are consistent with the star being still
a fast rotator. We find again the well-known mass-discrepancy for this
star. Conclusions: We conclude that the star follows the WLR
expected for its metallicity. The results are consistent with GHV-62024
being a fast rotator seen close to pole-on, strongly contaminated at the
surface with CNO products and with a wind structure altered by the fast
rotation but without modifying the global WLR. We suggest that this
could be a general property of fast rotators.
Based on observations obtained at the ESO VLT for Programmes 078.D-0767
and 080.D-0423.
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