Obscured clusters. I. GLIMPSE30 - A young milky way star cluster hosting Wolf-Rayet stars

Abstract

Context. Young massive clusters are usually deeply embedded in dust and gas. They represent excellent astrophysical laboratories for the study of massive stars. Clusters with Wolf-Rayet (WR) stars are of special importance, since this enables us to study a coeval WR population at a uniform metallicity and known age. Aims. We started a long- term project to search the inner Milky Way for hidden star clusters and to study them in detail. GLIMPSE 30 (G30) is one of these clusters. It is situated near the Galactic plane (l = 298 degrees 756, b = - 0 degrees.408) and we determine its physical parameters and investigate its high-mass stellar content especially WR stars. Methods. Our analysis is based on SOFI/NTT J(S)HK(S) imaging and low resolution (R similar to 2000) spectroscopy of the brightest cluster members in the K atmospheric window. For the age determination we applied isochrone fits for MS and Pre- MS stars. We derived stellar parameters of the WR stars candidates using a full nonLTE modeling of the observed spectra. Results. Using a variety of techniques we found that G30 is very young cluster, with age t approximate to 4Myr. The cluster is located in the Carina spiral arm, it is deeply embedded in dust and su. ers reddening of A(v) similar to 10.5 +/- 1.1 mag. The distance to the object is d = 7.2 +/- 0.9 kpc. The mass of the cluster members down to 2.35M(circle dot) is similar to 1600M(circle dot) . The cluster's MF for the mass range of 5.6 to 31.6M(circle dot) shows a slope of G = - 1.01 +/- 0.03. The total mass of the cluster obtained by this MF down to 1M(circle dot) is about 3 x 103 M-circle dot. The spectral analysis and the models allow us to conclude that at least one Ofpe/WN and two WR stars can be found in G30. The WR stars are of the WN6-7 hydrogen rich type with progenitor masses of more than 60M(circle dot). Conclusions. G30 is a new member of the family of young Galactic clusters hosting WR stars. It is a factor of two to three less massive than some of the youngest super-massive star clusters like Arches, Quintuplet and the Central cluster and is their smaller analog.