The distant young embedded stellar cluster CBJC 8 associated with G085.40-0.00

摘要

Context. The infrared cluster CBJC 8 is associated with a 6.7 GHz methanol maser and a compact radio-continuum source, G85.40-0.00. It is located at a distance of about 8 kpc. Aims. The aim is to study the characteristics of this distant and compact embedded cluster and derive the properties of its stellar population. Methods. We present new ground-based near- and mid-infrared imaging observations of this region. The calibrated images were analysed together with archive Spitzer IRAC images. Results. Based on the discovery of a considerable fraction of embedded sources with infrared excess emission that are concentrated within a radius around 16″ centred near the position of the compact HII region G85.40-0.00, we were able to confirm the presence of a very young embedded cluster. It was found to contain more than 58 members brighter than M_K = 2.6, two-thirds of which showing significant near- or mid-IR excess emission. We present spectral energy distributions and extrapolated total luminosities for nine sources with large mid-infrared excesses that were measured in all four IRAC bands. For the brightest of these, G8540A, which is associated with a methanol maser and a compact HII region, we fitted a model of an infalling envelope plus disc plus central star to its observed 1.6 to 850 μm fluxes to get an idea of its physical properties. We also report a single 2.12 μm molecular hydrogen line emission knot near the centre of the cluster, which support the idea about an outflow activity.