Characterisation of young stellar clusters

Abstract

Aims. Several embedded clusters are found in the Galaxy. Depending on the formation scenario, most of them can evolve to unbounded groups that are dissolved within 10 Myr to 20 Myr. A systematic study of young stellar clusters that show distinct characteristics provides interesting information on the evolutionary phases during the pre-main sequence. To identify and to understand these phases we performed a comparative study of 21 young stellar clusters. Methods. Near-infrared data from 2MASS were used to determine the structural and fundamental parameters based on surface stellar density maps, radial density profile, and colour-magnitude diagrams. The cluster members were selected according to their membership probability, which is based on the statistical comparison with the cluster proper motion. Additional members were selected on the basis of a decontamination procedure that was adopted to distinguish field stars found in the direction of the cluster area. Results. We obtained age and mass distributions by comparing pre-main sequence models with the position of cluster members in the colour-magnitude diagram. The mean age of our sample is ∼5 Myr, where 57% of the objects is found in the 4-10 Myr range of age, while 43% is <4 Myr old. Their low E(B − V) indicate that the members are not suffering high extinction (A V < 1 mag), which means they are more likely young stellar groups than embedded clusters. Relations between structural and fundamental parameters were used to verify differences and similarities that could be found among the clusters. The parameters of most of the objects show the same trends or correlations. Comparisons with other young clusters show similar relations among mass, radius, and density. Our sample tends to have larger radius and lower volumetric density than embedded clusters. These differences are compatible with the mean age of our sample, which we consider intermediate between the embedded and the exposed phases of the stellar clusters evolution.

Open clusters

“…Our age determinations are in very good agreement with values found in the literature (Forbes & Short 1994;Kopchev et al 2006;Bukowiecki et al 2011;Santos-Silva & Gregorio-Hetem 2012). However, we find a true distance modulus greater than 0.5 mag compared with previous determinations (11.2-11.57 mag) locating the cluster far away and in a higher reddening region.…”

“…All the values agree very well (between 1.65 and 1.8 kpc). The colour excess E(B − V) ranges from 0.28 mag to 0.46 mag and the cluster age is estimated between 1 and 38 Myr (Vogt & Moffat 1973;Fitzgerald et al 1979a;Forbes & Short 1994;Rastorguev et al 1999;Kharchenko et al 2005Kharchenko et al , 2009bKopchev et al 2006;Bukowiecki et al 2011;Santos-Silva & Gregorio-Hetem 2012).…”

Tracing the Galactic spiral structure with embedded clusters

“…They suggest that an irregular GMC (or complex) may form massive stars simultaneously and their winds and/or supernova explosions may produce a second generation of massive stars propagating the star formation and producing star clusters with similar age. The ECs formation is quite rapid and probably range from 0.5 − 5 Myr ( 2007; Tamburro et al 2009;Santos-Silva & Gregorio-Hetem 2012;Camargo et al 2013). According to Camargo et al (2013), the deep embedded phase for most Galactic ECs ends before 3Myr (Ballesteros-Paredes et al 2007;de la Fuente Marcos & de la Fuente Marcos 2009b).…”

Study of open clusters within 1.8 kpc and understanding the Galactic structure

“…Studies like this have already been carried out by many authors on the basis of the DAML02 open cluster catalog (Dias et al 2002), the sample of which is updated with recently published data on the star clusters 1 . Over the past ten years, Tadross et al (2002), Joshi (2005), Bonatto et al (2006), Bonatto & Bica (2011), Santos-Silva & Gregorio-Hetemand (2012), Buckner & Froebrich (2014), and many others have used this catalog to study the Galactic structure in great detail. However, the Dias catalog is heterogeneous in nature because a variety of techniques and observational setups were used by different authors to derive the cluster parameters.…”