IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Modelling chromospheric line profiles as diagnostics of velocity fields in ω Centauri red giant stars
Autor/es:
M. VIEYTES; P. MAUAS; C. CACCIARI; L. ORIGLIA; E. PANCINO
Lugar:
Salta
Reunión:
Congreso; Reunión de la Asociación Argentina de Astronomía; 2010
Institución organizadora:
IATE- Universidad Nacional de Salta
Resumen:
Context. Mass loss of ~0.1−0.3 M⊙ from
Population II red giant stars (RGB) is a requirement of stellar
evolution theory in order to account for several observational evidences
in globular clusters.
Aims. The aim of this study is to detect the presence
of outward velocity fields, which are indicative of mass outflow, in six
luminous red giant stars of the stellar cluster ω Cen.
Methods. We compare synthetic line profiles computed using relevant model chromospheres to observed profiles of the Hα and Ca II K lines. The spectra were taken with UVES (R = 45
000) and the stars were selected so that three of them belong to the
metal-rich population and three to the metal-poor population, and sample
as far down as 1 to 2.5 mag fainter than the respective RGB tips.
Results. We do indeed reveal the presence of
low-velocity outward motions in four of our six targets, without any
apparent correlation with astrophysical parameters.
Conclusions. This provides direct evidence that
outward velocity fields and mass motions exist in RGB stars as much as
2.5 mag fainter than the tip. On the assumption that the mass outflow
may eventually lead to mass loss from the star, we estimate mass-loss
rates of some 10-9−10-10 M⊙ yr-1
that are compatible with the stellar evolution requirements. These
rates seem to be correlated with luminosity rather than metallicity.