97 research outputs found
Determination of fundamental properties of an M31 globular cluster from main-sequence photometry
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 Gyr, the reddening value
E(B-V)=0.08, and the distance modulus .Comment: Accepted for Publication in PASP, 7 pages, 1 figure and 1 tabl
Spectral Energy Distributions of M81 Globular Clusters in BATC Multicolor Survey
In this paper, we give the spectral energy distributions of 42 M81 globular
clusters in 13 intermediate-band filters from 4000 to 10000 A, using the CCD
images of M81 observed as part of the BATC multicolor survey of the Sky. The
BATC multicolor filter system is specifically designed to exclude most of the
bright and variable night-sky emission lines including the OH forest. Hence, it
can present accurate SEDs of the observed objects. These spectral energy
distributions are low-resolution spectra, and can reflect the stellar
populations of the globular clusters. This paper confirms the conclusions of
Schroder et al. that, M81 contains clusters as young as a few Gyrs, which also
were observed in both M31 and M33Comment: Accepted for Publication in PASP, 10 pages, 3 figure
Color and Metallicity Distributions of M81 Globular Clusters
In this paper we present catalogs of photometric and spectroscopic data for
M81 globular clusters (GCs). The catalogs include B- and V- photometric and
reddening data of 95 GCs, and spectroscopic metallicities of 40 GCs in M81.
Using these data, we make some statistical correlations. The results show that
the distributions of intrinsic B and V colors and metallicities are bimodal,
with metallicity peaks at [Fe/H]=-1.45 and -0.53, respectively as has been
demonstrated for our Milky Way and M31. The relation between spectroscopic
metallicity and intrinsic B and V color also exists as it does for the Milky
Way and M31.Comment: Accepted for Publication in PASP, 9 pages, 6 figure
037-B327 in M31: Luminous Globular Cluster or Core of a Former Dwarf Spheroidal Companion to M31?
037-B327 is of interest because it is both the most luminous and the most
highly reddened cluster known in M31. Deep observations with the Advanced
Camera for Surveys on the Hubble Space Telescope provide photometric data in
the F606W band, and also show that this cluster is crossed by a dust lane. We
determined the structural parameters of 037-B327 by fitting the observed
surface brightness distribution to a King model with r_c=0.72" (=2.69 pc), and
r_t=5.87" (=21.93 pc), and a concentration index c=log(r_t/r_c)=0.91. The
surface brightness profile appears to be essentially flat within 0.25" of the
center and shows no signs of core collapse. Although the dust lane affects the
photometry, the King model fits the surface brightness profile well except for
the regions badly affected by the dust lane. We also calculate the half-light
radius r_h=1.11" (=4.15 pc). Combined with previous photometry, we find that
this object falls in the same region of the M_V versus log R_h diagram as do
Omega Centauri, M54 and NGC 2419 in the Milky Way and the massive cluster G1 in
M31. All four of these objects have been claimed to be the stripped cores of
former dwarf galaxies. This suggests that 037-B327 may also be the stripped
core of a former dwarf companion to M31.Comment: Accepted for Publication in ApJ Letter, 4 pages, 4 figure
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