A very young star forming region detected by the ISOPHOT Serendipity Survey

We present a multi-wavelength study of the star forming region ISOSS J 20298+3559, which was identified by a cross-correlation of cold compact sources from the 170 mu m ISOPHOT Serendipity Survey (ISOSS) database coinciding with objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J 20298+3559 is associated with a massive dark cloud complex (M ~ 760 M_sun) and located in the Cygnus X giant molecular cloud. We derive a distance of 1800 pc on the basis of optical extinction data. The low average dust temperature (T ~ 16 K) and large mass (M ~ 120 M_sun) of the dense inner part of the cloud, which has not been dispersed, indicates a recent begin of star formation. The youth of the region is supported by the early evolutionary stage of several pre- and protostellar objects discovered across the region: I) two candidate Class 0 objects with masses of 8 and 3.5 M_sun, II) a gravitationally bound, cold (T ~ 12 K) and dense (n(H₂) ~ 2 x 10⁵ cm^-3) cloud core with a mass of 50 M_sun and III) a Herbig B2 star with a mass of 6.5 M_sun and a bolometric luminosity of 2200 L_sun, showing evidence for ongoing accretion and a stellar age of less than 40 000 years. The dereddened SED of the Herbig star is well reproduced by an accretion disc + star model. The externally-heated cold cloud core is a good candidate for a massive pre-protostellar object. The star formation efficiency in the central cloud region is about 14%.

Based on observations with the James-Clerk-Maxwell Telescope JCMT, the IRAM 30 m Telescope, the United Kingdom Infrared Telescope UKIRT, the MPIfR 100 m Telescope, the Calar Alto Observatory and the Infrared Space Observatory ISO, an ESA project funded by Member States (especially France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.