Near infrared photometric and optical spectroscopic study of 22 low mass star clusters embedded in nebulae^*

¹ Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501–970, RS, Brazil e-mail: jules@if.ufrgs.br
² LATO-DCET-UESC, Rodovia Ilhéus-Itabuna, km 16, Ilhéus 45662-000, BA, Brazil
³ Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina

Received: 4 May 2007
Accepted: 3 October 2007

Abstract

Aims.Among the star clusters in the Galaxy, those embedded in nebulae represent the youngest group, which has only recently been explored. The analysis of a sample of 22 candidate embedded stellar systems in reflection nebulae and/or HII environments is presented.

Methods.We employed optical spectroscopic observations of stars in the directions of the clusters carried out at CASLEO (Argentina) together with near infrared photometry from the 2MASS catalogue. Our analysis is based on source surface density, colour-colour diagrams and on theoretical pre-main sequence isochrones. We take into account the field star contamination by carrying out a statistical subtraction.

Results.The studied objects have the characteristics of low mass systems. We derive their fundamental parameters. Most of the cluster ages are younger than 2 Myr. The studied embedded stellar systems in reflection nebulae and/or HII region complexes do not have stars of spectral types earlier than B. The total stellar masses locked in the clusters are in the range 20-220 . They are found to be gravitationally unstable and are expected to dissolve in a timescale of a few Myr.