Issue |
A&A
Volume 392, Number 1, September II 2002
|
|
---|---|---|
Page(s) | 115 - 129 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20020840 | |
Published online | 22 August 2002 |
Does the mixing length parameter depend on metallicity?
Further tests of evolutionary sequences using homogeneous databases
1
Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: palmieri,piotto; lgirardi@pd.astro.it
2
European Southern Observatory, 3107 Alonso de Cordova, Casilla 19001, Santiago 19, Chile e-mail: isaviane@eso.org
3
Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy e-mail: lgirardi@ts.astro.it
4
Dipartimento di Fisica, Università di Pisa, Piazza Torricelli 2, 56100 Pisa, Italy e-mail: vittorio@astr18pi.difi.unipi.it
Corresponding author: G. Piotto, piotto@pd.astro.it
Received:
5
April
2002
Accepted:
3
May
2002
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 WHB vs. metallicity, originally proposed by Brocato
et al. ([CITE]; 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 WHB-[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-Teff
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 -temperature relations is needed.
Key words: stars: evolution / stars: Hertzsprung-Russell (HR) and C-M diagrams / stars: horizontal-branch / stars: Population II / Galaxy: globular clusters: general / Galaxy: halo
© ESO, 2002
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