Determination of fundamental properties of an M31 globular cluster from main-sequence photometry

Kavli Affiliate: Jiansheng Chen

| First 5 Authors: Jun Ma, Zhenyu Wu, Song Wang, Zhou Fan, Xu Zhou

| Summary:

M31 globular cluster B379 is the first extragalactic cluster, the age of
which was determined by main-sequence photometry. In this method, the age of a
cluster is obtained by fitting its CMD with stellar evolutionary models.
However, different stellar evolutionary models use different parameters of
stellar evolution, such as range of stellar masses, different opacities and
equations of state, and different recipes, and so on. So, it is interesting to
check whether different stellar evolutionary models can give consistent results
for the same cluster. Brown et al. (2004a) constrained the age of B379 by
comparing its CMD with isochrones of the 2006 VandenBerg models. Using SSP
models of BC03 and its multi-photometry, Ma et al. (2007) independently
determined the age of B379, which is in good agreement with the determination
of Brown et al. (2004a). The BC03 models are calculated based on the Padova
evolutionary tracks. It is necessary to check whether the age of B379 which,
being determined based on the Padova evolutionary tracks, is in agreement with
the determination of Brown et al. (2004a). So, in this paper, we re-determine
its age using isochrones of the Padova stellar evolutionary models. In
addition, the metal abundance, the distance modulus, and the reddening value
for B379 are also determined in this paper. The results obtained in this paper
are consistent with the previous determinations, which including the age
obtained by Brown et al. (2004a). So, this paper confirms the consistence of
the age scale of B379 between the Padova isochrones and the 2006 VandenBerg
isochrones, i.e. the results’ comparison between Brown et al. (2004a) and Ma et
al. (2007) is meaningful. The results obtained in this paper are: the
metallicity [M/H]=-0.325, the age $tau=11.0pm1.5$ Gyr, the reddening value
E(B-V)=0.08, and the distance modulus $(m-M)_{0}=24.44pm0.10$.

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