Homogeneous photometry and star counts in the field of 9 Galactic star clusters
Authors
Anton Seleznev (1), Giovanni Carraro (2), Edgardo Costa (3), and Alexhander Loktin (1)
Affiliation
(1) Ural State University
(2) ESO-Chile
(3) Universidad de Chile
Accepted by
New Astronomy
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Abstract
We present homogeneous V,I CCD photometry of nine stellar fields in the two
inner quadrants
of the Galactic plane. The lines-of-view to most of these fields aim in the dire
ction of the very
inner Galaxy, where the Galactic field is very dense, and extinction is high and
patchy. Our
nine fields are, according to several catalogs, centred on Galactic star clusters,
namely
Trumpler 13, Trumpler 20, Lynga 4, Hogg 19, Lynga 12, Trumpler 25, Trumpler 26,
Ruprecht 128, and Trumpler 34. Apart from their coordinates, and in some cases
additional
basic data (mainly from the 2MASS archive), their properties are poorly known. By
means of star
count techniques and field star decontaminated Color-Magnitude diagrams, the
nature and size of
these visual over-densities has been established; and, when possible, new cluster
fundamental
parameters have been derived. To strengthen our findings, we complement our data
-set with JHKs
photometry from the 2MASS archive, that we analyze using a suitably defined
Q-parameter.
Most clusters are projected towards the Carina-Sagittarium spiral arm.
Because of that, we detect in the Color Magnitude Diagrams
of most of the other fields several distinctive sequences produced by young popu
lation within
the arm.
All the clusters are of intermediate or
old age. The most interesting cases detected by our study are, perhaps, that of
Trumpler 20,
which seems to be much older than previously believed, as indicated by its promiment
-and double- red clump;
and that of Hogg 19, a previously overlooked old open cluster,
whose existence in such regions of the Milky Way is puzzling.