Issue |
A&A
Volume 462, Number 1, January IV 2007
|
|
---|---|---|
Page(s) | 107 - 122 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20054197 | |
Published online | 24 October 2006 |
Monte Carlo simulations of metal-poor star clusters *,**
1
Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, 56126 Pisa, Italy e-mail: raimondo@oa-teramo.inaf.it
2
INFN, Sezione di Pisa, Largo B. Pontecorvo 3, 56126 Pisa, Italy
3
INAF, Osservatorio Astronomico di Teramo, via M. Maggini, 64100 Teramo, Italy
Received:
13
September
2005
Accepted:
7
August
2006
Context.Metal-poor globular clusters (GCs) can provide a probe of the earliest epoch of star formation in the Universe, being the oldest observable stellar systems. In addition, young and intermediate-age low-metallicity GCs are present in external galaxies. Nevertheless, inferring their evolutionary status by using integrated properties may suffer from large intrinsic uncertainty caused by the discrete nature of stars in stellar systems, especially in the case of faint objects.
Aims.In this paper, we evaluate the intrinsic uncertainty (due
to statistical effects) affecting the integrated colours and
mass-to-light ratios as a function of the cluster's integrated
visual magnitude (), which represents a directly
measured quantity. We investigate the case of metal-poor,
single-burst stellar populations with age from a few million years
to a likely upper value for the Galactic globular cluster ages
(~15 Gyr).
Methods.Our approach is based on Monte Carlo techniques for randomly generating stars distributed according to the cluster's mass function.
Results.Integrated colours and mass-to-light ratios in different
photometric bands are checked for good agreement with the
observational values of low-metallicity Galactic clusters; the
effect of different assumptions on the horizontal branch (HB)
morphology is shown to be irrelevant, at least for the photometric
bands explored here. We present integrated colours and
mass-to-light ratios as a function of age for different
assumptions on the cluster total V magnitude. We find that the
intrinsic uncertainty cannot be neglected. In particular,
in models with the broad-band colours show an
intrinsic uncertainty high enough to prevent the precise
age of the cluster from being evaluated. The effects of different
assumptions on the initial mass function and on the minimum mass
for which carbon burning is ignited for both integrated colours
and mass-to-light ratios are also analysed. Finally, the present
predictions are compared with recent results available in the
literature, showing non-negligible differences in some cases.
Key words: stars: evolution / Galaxy: globular clusters: general / galaxies: star clusters
© ESO, 2007
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