13 research outputs found
Detailed study of B037 based on {\sl HST} images
B037 is of interest because it is both the most luminous and the most highly
reddened cluster known in M31. Images of deep observations and of highly
spatial resolutions with the Advanced Camera for Surveys on the {\sl HST}
firstly show that this cluster is crossed by a dust lane. Photometric data in
the F606W and F814W filters obtained in this paper provide that, colors of
() in the dust lane are redder mags than ones in
the other regions of B037. The {\sl HST} images show that, this dust lane seems
to be contained in B037, not from the M31 disk or the Milky Way. As we know,
the formation of dust requires gas with a rather high metallicity. However,
B037 has a low metallicity to be . So, it seems
improbable that the observed dust lane is physically associated with B037. It
is clear that the origin of this dust lane is worthy of future study. In
addition, based on these images, we present the precise variation of
ellipticity and position angle, and of surface brightness profile, and
determine the structural parameters of B037 by fitting a single-mass isotropic
King model. In the F606W filter, we derive the best-fitting scale radius,
r_0=0.56\pm0.02\arcsec~(=2.16\pm0.08~\rm{pc}), a tidal radius,
r_t=8.6\pm0.4\arcsec~(=33.1\pm1.5~\rm{pc}), and a concentration index . In the F814W filter, we derive
r_0=0.56\pm0.01\arcsec~(=2.16\pm0.04~\rm{pc}),
r_t=8.9\pm0.3\arcsec~(=34.3\pm1.2~\rm{pc}), and . The extinction-corrected central surface brightness is
in the F606W filter, and in the F814W filter, respectively.Comment: Accepted for Publication in RAA, 13 pages, 5 figures and 7 table
Is KR Cygni a Triple Star System?
New multi-color UBVR light curves of the eclipsing binary KR Cyg were
obtained in 2005. Photometric solutions were derived using the Wilson- Devinney
method. The result shows that KR Cyg is a near-contact binary system with a
large effective temperature difference between the components, approximately
5230 K. All the times of minimum light were collected and combined with our
observations obtained in 2010 and 2011. Analysing all the times of mid-eclipse,
we found for the first time a possible periodic oscillation with an amplitude
of 0.001 days and a period of ~76 years. The periodic oscillation could be
explained by the light-time effect due to a presumed third component.Comment: 19 pages, 6 figure
Star Clusters in M31: I. A Catalog and a Study of the Young Clusters
We present an updated catalog of 1300 objects in the field of M31, including
670 likely star clusters of various types. Archival images were inspected to
confirm cluster classifications where possible, but most of the classifications
were based on spectra taken of ~1000 objects with the Hectospec fiber
positioner and spectrograph on the 6.5m MMT. The spectra and images of young
clusters are analyzed in detail in this paper. Ages, reddenings and masses of
140 young clusters are derived by comparing the observed spectra and photometry
with model spectra. We find these to have masses as great as 10^5 with a median
of 10^4 M_sun, and a median age of 0.25 Gyr. Thus these clusters are similar in
mass to the LMC young massive clusters, and are in between Milky Way open
clusters and the globulars of M31 and the Milky Way. Most of the M31 young
clusters have the low concentration typical of Milky Way open clusters, and we
expect that most of these will be disrupted in the next Gyr, but a few have
high concentrations and will likely survive longer. The spatial distribution of
the young clusters is well correlated with the star-forming regions as mapped
out by mid-IR emission. A kinematic analysis likewise confirms the spatial
association of the young clusters with the young disk in M31.Comment: 18 pages of text and figures, 23 of tables, to appear in AJ.
http://www.cfa.harvard.edu/oir/eg/m31clusters/M31_Hectospec.html is a new M31
web site containing tables and postage stamp images of the entire catalo
The outermost cluster of M31
We report on the identification of a new cluster in the far halo of the M31
galaxy. The cluster, named Bologna 514 (B514) has an integrated magnitude
M_V=-8.5 +- 0.6, and a radial velocity, as estimated from two independent
low-resolution spectra, V_r=-456 +- 23 km/s, which fully confirms its
membership to the M31 system. The observed integrated spectrum is very similar
to those of classical globular clusters. Being located at ~ 4^o (~55 kpc in
projected distance) from the center of the parent galaxy, B514 is by far the
most remote M31 cluster ever discovered. Its projected position, near the
galaxy major axis, and M31-centric velocity, similar to that observed in the
outermost regions of the HI rotation curve, may indicate that it belongs to the
subsystem of M31 clusters that has been recently proposed (Morrison et al.
2004) to be part of the dynamically-cold thin disc of the galaxy.Comment: 6 pages, 4 figures, accepted for publication in A &
Spectral Energy Distributions and Age Estimates of 39 Globular Clusters in M31
This paper supplements Jiang et al. (2003), who studied 172 M31 globular
clusters (GCs) and globular cluster candidates from Battistini et al. (1987) on
the basis of integrated photometric measurements in the
Beijing-Arizona-Taiwan-Connecticut (BATC) photometric system. Here, we present
multicolor photometric CCD data (in the BATC system) for the remaining 39 M31
GCs and candidates. In addition, the ages of 35 GCs are constrained by
comparing our accurate photometry with updated theoretical stellar synthesis
models. We use photometric measurements from GALEX in the far- and
near-ultraviolet and 2MASS infrared data, in combination with optical
photometry. Except for two clusters, the ages of the other sample GCs are all
older than 1 Gyr. Their age distribution shows that most sample clusters are
younger than 6 Gyr, with a peak at ~3 Gyr, although the `usual' complement of
well-known old GCs (i.e., GCs of similar age as the majority of the Galactic
GCs) is present as well.Comment: Accepted for Publication in AJ, 18 pages, 5 figures, 5 table
Systematic differences in simple stellar population model results: Application to the M31 globular-like cluster system
Simple stellar population (SSP) synthesis models are useful tools for
studying the nature of unresolved star clusters in external galaxies. However,
the plethora of currently available SSP models gives rise to significant and
poorly documented systematic differences. Here we consider the outputs of the
commonly used Bruzual & Charlot and GALEV models, as well as a recently updated
SSP model suite which attempts to include the contributions of binary merger
products in the form of blue straggler stars (BS-SSP). We rederive the ages,
metallicities, extinction values and masses of 445 previously observed
globular-like clusters in M31 based on chi-square minimisation of their
spectral energy distributions with respect to these three different SSP models
and adopting a Chabrier-like stellar initial mass function. A comparison
between our new results and previous estimates of the same parameters shows
that the Bruzual & Charlot models yield the youngest ages and lowest masses,
while adoption of the BS-SSP models results in the oldest ages and highest mass
estimates. Similarly, the GALEV SSP models produce the lowest metallicities,
with the highest values resulting from the BS-SSP model suite. These trends are
caused by intrinsic differences associated with the models, and are not
significantly affected by the well-known age-metallicity degeneracy. Finally,
we note that the mass function of the massive M31 star clusters is similar to
that of the Milky Way's globular clusters, which implies that the two star
cluster systems likely formed under similar environmental conditions.Comment: 15 pages, 12 figures, 2 tables, accepted for publication in MNRA
Globular cluster luminosity function as distance indicator
Globular clusters are among the first objects used to establish the distance
scale of the Universe. In the 1970-ies it has been recognized that the
differential magnitude distribution of old globular clusters is very similar in
different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the
so-called Globular Cluster Luminosity Function has been then established as a
secondary distance indicator. The intrinsic accuracy of the method has been
estimated to be of the order of ~0.2 mag, competitive with other distance
determination methods. Lately the study of the Globular Cluster Systems has
been used more as a tool for galaxy formation and evolution, and less so for
distance determinations. Nevertheless, the collection of homogeneous and large
datasets with the ACS on board HST presented new insights on the usefulness of
the Globular Cluster Luminosity Function as distance indicator. I discuss here
recent results based on observational and theoretical studies, which show that
this distance indicator depends on complex physics of the cluster formation and
dynamical evolution, and thus can have dependencies on Hubble type, environment
and dynamical history of the host galaxy. While the corrections are often
relatively small, they can amount to important systematic differences that make
the Globular Cluster Luminosity Function a less accurate distance indicator
with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review
paper based on the invited talk at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13
pages, 8 figures