INAF-IASF, Sez. di Roma, via Fosso del Cavaliere 100,
2 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 877, Ensenada, Baja California, CP 22830, Mexico
3 Observatorio Astronómico de Córdoba, Córdoba, Argentina
Received: 12 April 2010
Accepted: 30 September 2010
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 MK = 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.
Key words: stars: formation / HII regions / ISM: clouds / masers / stars: protostars / ISM: jets and outflows
Based on observations made with the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, and at the Observatorio Astronómico Nacional, San Pedro Mártir, B.C, Mexico. This work uses archive observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.
The photometric data tables are only available in electronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsweb.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A1
© ESO, 2010