Detalles de publicación

PP 010083

On the magnitude difference between the main sequence turn off and the red giant branch bump in Galactic globular clusters

S. Cassisi(1), A. Marín-Franch(2,3), M. Salaris(4), A. Aparicio(5, 6) , M. Monelli(6, 5), A. Pietrinferni(1)
(1) INAF - Osservatorio Astronomico di Teramo, (2) Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA), (3) Departamento de Astrofisica, Universidad Complutense de Madrid, (4) Astrophysics Research Institute, Liverpool John Moores University, (5) Departamento de Astrofísica, Universidad de La Laguna, (6) IAC
We present new measurements of the magnitude of the main sequence turn off and the red giant branch bump in the luminosity function of a sample of Galactic globular clusters with updated estimates of [Fe/H] and [alpha/Fe], employing
photometric data collected with the Advanced Camera for Survey on board the HST.
We compare measured and predicted values of the magnitude difference between these two features, a rarely employed diagnostic of the internal structure of low-mass stars at the beginning of their red giant evolution.
Our analysis discloses a clear discrepancy between theory and observations, the theoretical red giant branch bump magnitudes being too bright by on average ~0.2mag. This corroborates results from the more widely studied magnitude difference between horizontal branch and red giant bump, avoiding the well known problems associated to the determination of the horizontal branch level from colour magnitude diagrams, and to uncertainties in the luminosity of horizontal branch stellar models. We briefly discuss several potential solutions of this discrepancy.

 
Aceptado para publicación en A&A | Enviado el 2010-12-02 | Proyecto 3E0394