Bibcode
Camacho, I.; Garcia, M.; Herrero, A.; Simón-Díaz, S.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 585, id.A82, 15 pp.
Fecha de publicación:
1
2016
Revista
Número de citas
27
Número de citas referidas
20
Descripción
Context. Massive stars play an important role in the chemical and
dynamical evolution of the Universe. The first metal-poor stars may have
started the reionization of the Universe. To understand these early
epochs it is necessary to know the behavior and the physical properties
of massive stars in very metal-poor environments. We focus on the
massive stellar content of the metal-poor irregular galaxy Sextans A.
Aims: Our aim is to find and classify OB stars in Sextans A, so
as to later determine accurate stellar parameters of these blue massive
stars in this low-metallicity region (Z ~ 0.1 Z⊙).
Methods: Using UBV photometry, the reddening-free index Q and GALEX
imaging, we built a list of blue massive star candidates in Sextans A.
We obtained low-resolution (R ~ 1000) GTC-OSIRIS spectra for a fraction
of them and carried out spectral classification. For the confirmed
O-stars, we derived preliminary stellar parameters. Results: The
target selection criteria and observations were successful and have
produced the first spectroscopic atlas of OB-type stars in Sextans A.
From the whole sample of 18 observed stars, 12 were classified as early
OB-types, including 5 O-stars. The radial velocities of all target stars
are in agreement with their Sextans A membership, although three of them
show significant deviations. We determined the stellar parameters of the
O-type stars using the stellar atmosphere code FASTWIND and revisited
the sub-SMC temperature scale. Two of the O-stars are consistent with
relatively strong winds and enhanced helium abundances, although results
are not conclusive. We discuss the position of the OB stars in the HRD.
Initial stellar masses run from slightly below 20 up to 40 solar masses.
Conclusions: The target selection method worked well for Sextans
A. The stellar temperatures are consistent with findings in other
galaxies. Some of the targets deserve follow-up spectroscopy because of
indications of a runaway nature, an enhanced helium abundance, or a
relatively strong wind. We observe a correlation between HI and OB
associations similar to the irregular galaxy IC 1613, confirming the
previous result that the most recent star formation of Sextans A is
currently ongoing near the rim of the H i cavity.
Based on observations made with the Gran Telescopio Canarias (GTC),
installed in the Spanish Observatorio del Roque de los Muchachos of the
Instituto de Astrofísica de Canarias, on the island of La Palma.
Programme ID GTC59-12A.The data are available through the GTC archive:
http://https://gtc.sdc.cab.inta-csic.es/gtc/jsp/searchres.jsp