427,064 research outputs found
Uncloaking globular clusters in the inner Galaxy
Extensive photometric studies of the globular clusters located towards the
center of the Milky Way have been historically neglected. The presence of
patchy differential reddening in front of these clusters has proven to be a
significant obstacle to their detailed study. We present here a well-defined
and reasonably homogeneous photometric database for 25 of the brightest
Galactic globular clusters located in the direction of the inner Galaxy. These
data were obtained in the B, V, and I bands using the Magellan 6.5m telescope
and the Hubble Space Telescope. A new technique is extensively used in this
paper to map the differential reddening in the individual cluster fields, and
to produce cleaner, dereddened color-magnitude diagrams for all the clusters in
the database. Subsequent papers will detail the astrophysical analysis of the
cluster populations, and the properties of the obscuring material along the
clusters' lines of sight.Comment: Accepted for publication in A
MASSCLEANage -- Stellar Cluster Ages from Integrated Colors --
We present the recently updated and expanded MASSCLEANcolors, a database of
70 million Monte Carlo models selected to match the properties (metallicity,
ages and masses) of stellar clusters found in the Large Magellanic Cloud (LMC).
This database shows the rather extreme and non-Guassian distribution of
integrated colors and magnitudes expected with different cluster age and mass
and the enormous age degeneracy of integrated colors when mass is unknown. This
degeneracy could lead to catastrophic failures in estimating age with standard
SSP models, particularly if most of the clusters are of intermediate or low
mass, like in the LMC. Utilizing the MASSCLEANcolors database, we have
developed MASSCLEANage, a statistical inference package which assigns the most
likely age and mass (solved simultaneously) to a cluster based only on its
integrated broad-band photometric properties. Finally, we use MASSCLEANage to
derive the age and mass of LMC clusters based on integrated photometry alone.
First we compare our cluster ages against those obtained for the same seven
clusters using more accurate integrated spectroscopy. We find improved
agreement with the integrated spectroscopy ages over the original photometric
ages. A close examination of our results demonstrate the necessity of solving
simultaneously for mass and age to reduce degeneracies in the cluster ages
derived via integrated colors. We then selected an additional subset of 30
photometric clusters with previously well constrained ages and independently
derive their age using the MASSCLEANage with the same photometry with very good
agreement. The MASSCLEANage program is freely available under GNU General
Public License.Comment: 17 pages, 11 figures. Accepted for publication in The Astrophysical
Journal. Full resolution figures available in journal versio
Broad-band photometric evolution of star clusters
I briefly introduce a database of models that describe the evolution of star
clusters in several broad-band photometric systems. Models are based on the
latest Padova stellar evolutionary tracks - now including the alpha-enhanced
case and improved AGB models - and a revised library of synthetic spectra from
model atmospheres. As of today, we have revised isochrones in
Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Thuan-Gunn, and Washington
systems. Several other filter sets are included in a preliminary way, like
those used by the EIS and SDSS projects. The database contains also integrated
magnitudes of single-burst stellar populations and Monte-Carlo simulations that
show the stochastic dispersion of the colours as a function of cluster mass,
age, and metallicity. The models are useful for several kinds of studies,
including estimates of masses and ages of extragalactic star clusters observed
by means of broad-band photometry.Comment: 5 pages, to appear in Extragalactic Star Clusters, IAU Symp 207, eds.
E.K. Grebel, D. Geisler, D. Minniti. The isochrone data is in
http://pleiadi.pd.astro.it/~lgirardi/isoc_photsys.htm
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