Bibcode
Castro, N.; Urbaneja, M. A.; Herrero, A.; Garcia, M.; Simón-Díaz, S.; Bresolin, F.; Pietrzyński, G.; Kudritzki, R.-P.; Gieren, W.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 542, id.A79
Advertised on:
6
2012
Revista
Número de citas
63
Número de citas referidas
53
Descripción
Context. The quantitative study of the physical properties and chemical
abundances of large samples of massive blue stars at different
metallicities is a powerful tool to understand the nature and evolution
of these objects. Their analysis beyond the Milky Way is challenging,
nonetheless it is doable and the best way to investigate their behavior
in different environments. Fulfilling this task in an objective way
requires the implementation of automatic analysis techniques that can
perform the analyses systematically, minimizing at the same time any
possible bias. Aims: As part of the ARAUCARIA project we carry
out the first quantitative spectroscopic analysis of a sample of 12
B-type supergiants in the galaxy NGC 55 at 1.94 Mpc away. By applying
the methodology developed in this work, we derive their stellar
parameters, chemical abundances and provide a characterization of the
present-day metallicity of their host galaxy. Methods: Based on
the characteristics of the stellar atmosphere/line formation code
fastwind, we designed and created a grid of models for the analysis of
massive blue supergiant stars. Along with this new grid, we implemented
a spectral analysis algorithm. Both tools were specially developed to
perform fully consistent quantitative spectroscopic analyses of low
spectral resolution of B-type supergiants in a fast and objective way.
Results: We present the main characteristics of our fastwind
model grid and perform a number of tests to investigate the reliability
of our methodology. The automatic tool is applied afterward to a sample
of 12 B-type supergiant stars in NGC 55, deriving the stellar
parameters, Si , C , N , O and Mg abundances. The results indicate that
our stars are part of a young population evolving towards a red
supergiant phase. For half of the sample we find a remarkable agreement
between spectroscopic and evolutionary masses, whilst for the rest
larger discrepancies are present, but still within the uncertainties.
The derived chemical composition hints to an average metallicity similar
to the one of the Large Magellanic Cloud, with no indication of a
spatial trend across the galaxy. Conclusions: The consistency
between the observed spectra and our stellar models supports the
reliability of our methodology. This objective and fast approach allows
us to deal with large samples in an accurate and more statistical way.
These are two key issues to achieve an unbiased characterization of the
stars and their host galaxies.
Based on observations obtained at the ESO VLT Large Programme
171.D-0004.
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Propiedades Físicas y Evolución de Estrellas Masivas
Las estrellas masivas son objetos claves para la Astrofísica. Estas estrellas nacen con más de 8 masas solares, lo que las condena a morir como Supernovas. Durante su rápida evolución liberan, a través de fuertes vientos estelares, gran cantidad de material procesado en su núcleo y, en determinadas fases evolutivas, emiten gran cantidad de
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Simón Díaz