Paper: astro-ph/0512171
Date: Wed, 7 Dec 2005 04:21:20 GMT (201kb)

Title: 037-B327 in M31: Luminous Globular Cluster or Core of a Former Dwarf
Spheroidal Companion to M31?

Authors: Jun Ma (1), Sidney van den Bergh (2), Hong Wu, Yanbin Yang, Xu Zhou,
Jiansheng Chen, Zhenyu Wu, Zhaoji Jiang, Jianghua Wu ((1)National
Astronomical Observatories, Chinese Academy of Sciences; (2) Dominion
Astrophysical Observatory, Herzberg Institute of Astrophysics, National
Research Council, Canada)

Comments: Accepted for Publication in ApJ Letter, 4 pages, 4 figures
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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.

\\ ( http://arXiv.org/abs/astro-ph/0512171 , 201kb)

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Paper: astro-ph/0512172
Date: Wed, 7 Dec 2005 04:47:46 GMT (623kb)

Title: Age Estimations of M31 Globular Clusters from Their Spectral Energy
Distributions

Authors: Jun Ma (1), Xu Zhou, David Burstein (2), Yanbin Yang, Zhou Fan,
Jiansheng Chen, Zhaoji Jiang, et al. ((1)National Astronomical Observatories,
Chinese Academy of Sciences, (2)Department of Physics and Astronomy, Arizona
State University, Tempe, AZ)

Comments: Accepted for Publication in A&Ap, 13 pages, 6 figures
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This paper presents accurate spectral energy distributions (SEDs) of 16 M31
globular clusters (GCs) confirmed by spectroscopy and/or high
spatial-resolution imaging, as well as 30 M31 globular cluster candidates
detected by Mochejska et al. Most of these candidates have m_V > 18, deeper
than previous searches, and these candidates have not yet been confirmed to be
globular clusters. The SEDs of these clusters and candidates are obtained as
part of the BATC Multicolor Survey of the Sky, in which the
spectrophotometrically-calibrated CCD images of M31 in 13 intermediate-band
filters from 4000 to 10000 A were observed. These filters are specifically
designed to exclude most of the bright and variable night-sky emission lines
including the OH forest. In comparison to the SEDs of true GCs, we find that
some of the candidate objects are not GCs in M31. SED fits show that
theoretical simple stellar population (SSP) models can fit the true GCs very
well. We estimate the ages of these GCs by comparing with SSP models. We find
that, the M31 clusters range in age from a few ten Myr to a few Gyr old, as
well as old GCs, confirming the conclusion that has been found by Barmby et a,
Williams & Hodge, Beasley et al., Burstein et al. and Puzia et al. in their
investigations of the SEDs of M31 globular clusters.

\\ ( http://arXiv.org/abs/astro-ph/0512172 , 623kb)