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New Galactic Star Clusters Discovered in the VVV Survey

J. Borissova, C. Bonatto, R. Kurtev, J. R. A. Clarke, F. Peñaloza, S. E. Sale, D. Minniti, J. Alonso-García, E. Artigau, R. Barbá, E. Bica, G. L. Baume, M. Catelan, A.-N. Chené, B. Dias, S. L. Folkes, D. Froebrich, D. Geisler, R. de Grijs, M. M. Hanson, M. Hempel, V. D. Ivanov, M. S. N. Kumar, P. W. Lucas, F. Mauro, C. Moni-Bidin, M. Rejkuba, R. K. Saito, M. Tamura, I. Toledo

Abstract
Context. VISTA Variables in the Vía Láctea (VVV) is one of the six ESO Public Surveys operating on the new 4-meter Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages.
Aims. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources.
Methods. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated KS-band tile images for stellar overdensities. Subsequently, we examined the composite JHKS and ZJKS color images of each candidate. PSF photometry of 15 × 15 arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed.
Results. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solarmetallicity Padova isochrones to the color-magnitude diagrams.

Keywords
open clusters and associations: general – stars: early-type – infrared: general

Astronomy and Astrophysics
Volume 532, Number of pages A131_1
2011 August

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia