The embedded cluster DBSB 48 in the nebula Hoffleit 18: Comparison with Trumpler 14

Abstract

We derive fundamental parameters of the embedded cluster DBSB 48 in the southern nebula Hoffleit 18 and the very young open cluster Trumpler 14, by means of deep JHK s infrared photometry. We build colour-magnitude and colour-colour diagrams to derive reddening and age, based on main sequence and pre-main sequence distributions. Radial stellar density profiles are used to study cluster structure and guide photometric diagram extractions. Field-star decontamination is applied to uncover the intrinsic cluster sequences in the diagrams. Ages are inferred from Kexcess fractions. A prominent pre-main-sequence population is present in DBSB 48, and the K-excess fraction f K = 55 ± 6% gives an age of 1.1 ± 0.5 Myr. A mean reddening of A Ks = 0.9 ± 0.03 was found, corresponding to A V = 8.2 ± 0.3. The cluster CMD is consistent with the far kinematic distance of 5 kpc for Hoffleit 18. For Trumpler 14 we derived similar parameters as in previous studies in the optical, in particular an age of 1.7 ± 0.7 Myr. The fraction of stars with infrared excess in Trumpler 14 is f K = 28 ± 4%. Despite the young ages, both clusters are described by a King profile with core radii R core = 0.46 ± 0.05 pc and R core = 0.35 ± 0.04 pc, respectively for DBSB 48 and Trumpler 14. Such cores are smaller than those of typical open clusters. Small cores are probably related to the cluster formation and/or parent molecular cloud fragmentation. In DBSB 48, the magnitude extent of the upper main sequence is ∆ K s ≈ 2 mag, while in Trumpler 14 it is ∆ K s ≈ 5 mag, consistent with the estimated ages.

On the possible generation of the young massive open clusters Stephenson 2 and BDSB 122 by ω Centauri

“…BDSB 122 and Stephenson 2 are slightly closer to the Galactic centre than the Scutum-Crux arm. Several other young clusters from the catalogues of Bica et al (2003) and Dutra et al (2003) have already been studied in detail (e.g., Soares et al 2008;Ortolani et al 2008;Hanson & Bubnick 2008). We trace the orbits of both ω Centauri and Stephenson 2 backwards in time (and consequently, also that of BDSB 122) in the disk, testing an impact hypothesis for the origin of these two massive OCs.…”

“…2 from the catalogues of Bica et al (2003) and Dutra et al (2003) have already been studied in detail (e.g. Soares et al 2008;Ortolani et al 2008;Hanson & Bubnick 2008).…”

Constraining the star formation rate in the solar neighbourhood with star clusters

“…2MASS, 1 GLIMPSE 2 ), and some covering essentially all the sky (2MASS) has led to the discovery – and allowed a robust parameter derivation – of many such ECs (e.g. Bica et al 2003; Dutra et al 2003; Kumar, Kamath & Davis 2004; Bonatto, Santos & Bica 2006; Kumar, Keto & Clerkin 2006; Ortolani et al 2008; Bonatto & Bica 2009b,c, 2010a), together with some old and/or very reddened OCs (e.g. Bonatto & Bica 2007, 2008; Froebrich, Scholz & Raftery 2007; Bonatto & Bica 2009a, 2010b; Froebrich et al 2010).…”

“…2MASS 1 , GLIMPSE 2 , some covering essentially all the sky (2MASS), has led to the discovery -and allowed a robust parameter derivationof many such embedded clusters (ECs -e.g. Dutra et al 2003;Bica et al 2003;Kumar, Kamath & Davis 2004); Kumar, Keto & Clerkin 2006);Bonatto, Santos Jr. & Bica 2006;Ortolani et al 2008;Bonatto & Bica 2009b;Bonatto & Bica 2009c;Bonatto & Bica 2010a), together with some old and/or very reddened OCs (e.g. Froebrich, Scholz & Raftery 2007;Bonatto & Bica 2007;Bonatto & Bica 2009a;Froebrich et al 2010;Bonatto & Bica 2010b).…”

The early expansion of cluster cores

“…4. In the Galaxy there have been a number of massive young clusters discussed, including NGC 3603, Westerlund 1, Westerlund 2, the Arches and the Orion Nebula cluster (ONC; compilation taken from Brandner et al 2008; however, using an age of 1.5 Myr for the ONC –Jeffries 2007), NGC 2316 (Teixeira et al 2004), Trumpler 14 and DBSB48 (Ortolani et al 2008). Some massive extragalactic clusters have also been included, namely NGC 1569B (Larsen et al 2008), NGC 5236−805 (Larsen & Richtler 2004), NGC 6946−1447 (Larsen et al 2001), M82F (Bastian et al 2007, and references therein) and M82‐A1 (Smith et al 2006).…”