Exploring FSR open cluster candidates within of the Galactic anticentre

Universidade Federal do Rio Grande do Sul, Departamento de Astronomia CP 15051, RS, Porto Alegre 91501-970, Brazil e-mail: [charles;bica]@if.ufrgs.br

Received: 11 March 2008
Accepted: 21 April 2008

Abstract

Context. We investigate the nature of a sample of star cluster candidates detected as stellar overdensities towards the Galactic anticentre.

Aims. Taken from the catalogue of Froebrich, Scholz, and Raftery (FSR), the sample contains 28 star cluster candidates located within of the anticentre. These are all the candidates in that sector classified by FSR with a high probability of being star clusters. Our main goals are to determine the fraction of such candidates that are unknown star clusters, to derive their astrophysical parameters, and to investigate the relationship of cluster parameters with position in the Galaxy.

Methods. Properties of the star cluster candidates are investigated with field-star decontaminated 2MASS colour–magnitude diagrams and stellar radial density profiles.

Results. All candidates present significant excesses in the radial density profiles, consistent with the method from which they were originally selected. Of the 28 candidates, 7 are previously known open clusters, 2 have been recently identified, and 6 are new ones with ages from 30 Myr to 1 Gyr. Among the remaining 13 candidates, 6 are uncertain cases that require deeper observations, while 7 appear to be important field fluctuations. The structure of part of the newly identified open clusters appears to be affected by interaction with giant molecular clouds in the Local and Perseus arms.

Conclusions. When photometric and radial distribution properties are considered together, an important fraction of the stellar overdensities with a fluctuation level are shown to be star clusters. Thus, catalogues of star cluster candidates, coupled to the present kind of study, are an important source for identifying unknown open clusters. Such efforts affect the understanding of the star-formation rate, cluster dynamical evolution, and Galactic structure, among others.