Homogeneous photometry and star counts in the field of 9 Galactic star clusters

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 direction 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 JHK${}_s$ 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 population 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 prominent -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.

37 pages, 16 eps figures, in press in New Astronomy

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Cited by in corpus (14)

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• The Gaia-ESO Survey: Reevaluation of the parameters of the open cluster Trumpler 20 using photometry and spectroscopy
• Catalogue of variable stars in open cluster fields
• The effects of differential reddening and stellar rotation on the appearance of multiple populations in star clusters: the case of Trumpler 20
• Open-cluster density profiles derived using a kernel estimator
• Chemical abundance analysis of the old, rich open cluster Trumpler 20
• Photometric characterization of the Galactic star cluster Trumpler 20
• On the mass of the Galactic star cluster NGC 4337
• UBVI CCD photometry and star counts in 9 inner disk Galactic star clusters
• Five old open clusters more in the outer Galactic disk
• The complex stellar populations in the lines of sight to open clusters in the third Galactic quadrant
• NGC 4337: an over-looked old cluster in the inner disc of the Milky Way
• On the assessment of the nature of open star clusters and the determination of their basic parameters with limited data
• Star clusters with dual red clumps