Three intermediate-mass young stellar objects with different properties emerging from the same natal cloud in IRAS?00117+6412

摘要

Aims. Our main aim is to study the influence of theinitial conditions of a cloud in the intermediate/high-mass starformation process. Methods. We observed with the VLA, PdBI, and SMA thecentimeter and millimeter continuum, N2H+(1-0),and CO(2-1) emission associated with a dusty cloud harboringa nascent cluster with intermediate-mass protostars. Results. At centimeter wavelengths we found a strongsource, tracing a UCH II region, at theeastern edge of the dusty cloud, with a shell-like structure, and withthe near-infrared counterpart falling in the center of the shell. Thisis presumably the most massive source of the forming cluster. About15'' to the west of the UCH II region andwell embedded in the dusty cloud, we detected a strong millimetersource, MM1, associated with centimeter and near-infrared emission. MM1seems to be driving a prominent high-velocity CO bipolar outflowelongated in the northeast-southwest direction, and is embedded in aridge of dense gas traced by N2H+,elongated roughly in the same direction as the outflow. We estimatedthat MM1 is an intermediate-mass source in the Class 0/I phase. About15'' to the south of MM1, and still more deeply embedded in the dustycloud, we detected a compact millimeter source, MM2, with neithercentimeter nor near-infrared emission, but with water maser emission.MM2 is associated with a clump of N2H+,whose kinematics reveal a clear velocity gradient and additionally wefound signposts of infall motions. MM2, being deeply embedded withinthe dusty cloud, with an associated water maser but no hints of COoutflow emission, is an intriguing object, presumably of intermediatemass. Conclusions. The UCH IIregion is found at the border of a dusty cloud which is currentlyundergoing active star formation. Two intermediate-mass protostars inthe dusty cloud seem to have formed after the UCH IIregion and have different properties related to the outflow phenomenon.Thus, a single cloud with similar dust emission and similar dense gascolumn densities seems to be forming objects with different properties,suggesting that the initial conditions in the cloud are not determiningall the star formation process. Key words: stars: formation - dust,extinction - H II regions - ISM: individualobjects: IRAS00117+6412 - radio continuum: ISM