Martins, F.; Simón-Díaz, S.; Barbá, R. H.; Gamen, R. C.; Ekström, S.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 599, id.A30, 14 pp.
Fecha de publicación:
2
2017
Revista
Número de citas
20
Número de citas referidas
19
Descripción
Context. Massive star evolution remains only partly constrained. In
particular, the exact role of rotation has been questioned by puzzling
properties of OB stars in the Magellanic Clouds. Aims: Our goal
is to study the relation between surface chemical composition and
rotational velocity, and to test predictions of evolutionary models
including rotation. Methods: We have performed a spectroscopic
analysis of a sample of fifteen Galactic O7-8 giant stars. This sample
is homogeneous in terms of mass, metallicity and evolutionary state. It
is made of stars with a wide range of projected rotational velocities.
Results: We show that the sample stars are located on the second
half of the main sequence, in a relatively narrow mass range (25-40
M⊙). Almost all stars with projected rotational
velocities above 100 km s-1 have N/C ratios about ten times
the initial value. Below 100 km s-1 a wide range of N/C
values is observed. The relation between N/C and surface gravity is well
reproduced by various sets of models. Some evolutionary models including
rotation are also able to consistently explain slowly rotating, highly
enriched stars. This is due to differential rotation which efficiently
transports nucleosynthesis products and allows the surface to rotate
slower than the core. In addition, angular momentum removal by winds
amplifies surface braking on the main sequence. Comparison of the
surface composition of O7-8 giant stars with a sample of B stars with
initial masses about four times smaller reveal that chemical enrichment
scales with initial mass, as expected from theory. Conclusions:
Although evolutionary models that include rotation face difficulties in
explaining the chemical properties of O- and B-type stars at low
metallicity, some of them can consistently account for the properties of
main-sequence Galactic O stars in the mass range 25-40
M⊙.
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Proyecto IACOB: Una Nueva Era en el Estudio de Estrellas OB Galácticas
Massive stars has been many times claimed as Cosmic Engines and Gifts of Nature for the study of the Universe, from the Solar neighbourhood to the large-z Universe. The complete understanding of the physical properties and evolution of massive stars (and their interplay with the ISM) is crucial for many fields of Astrophysics and, ultimately, to
Sergio
Simón Díaz