2002A&A...392..115P -
Astronomy and Astrophysics, volume 392, 115-129 (2002/9-2)
Does the mixing length parameter depend on metallicity? Further tests of evolutionary sequences using homogeneous databases.
PALMIERI R., PIOTTO G., SAVIANE I., GIRARDI L. and CASTELLANI V.
Abstract (from CDS):
This paper is a further step in the investigation of the morphology of the color-magnitude diagram of Galactic globular clusters, and the fine-tuning of theoretical models, made possible by the recent observational efforts to build homogeneous photometric databases. In particular, we examine here the calibration of the morphological parameter W
HB vs. metallicity, originally proposed by Brocato et al. (
1998A&A...335..929B; B98), which essentially measures the color position of the red-giant branch. We show that the parameter can be used to have a first-order estimate of the cluster metallicity, since the dispersion around the mean trend with [Fe/H] is compatible with the measurement errors. The tight W
HB-[Fe/H] relation is then used to show that variations in helium content or age do not affect the parameter, whereas it is strongly influenced by the mixing-length parameter α (as expected). This fact allows us, for the first time, to state that there is no trend of α with the metal content of a cluster. A thorough examination of the interrelated questions of the α-elements enhancement and the color-T
eff transformations, highlights that there is an urgent need for an independent assessment of which of the two presently accepted metallicity scales is the true indicator of a cluster's iron content. Whatever scenario is adopted, it also appears that a deep revision of the V-I-temperature relations is needed.
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Journal keyword(s):
stars: evolution - stars: Hertzsprung-Russell (HR) and C-M diagrams - stars: horizontal-branch - stars: Population II - Galaxy: globular clusters: general - Galaxy: halo
Simbad objects:
49
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