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

¹ Centro de Astrobiología (INTA-CSIC), Laboratorio de Astrofísica Estelar y Exoplanetas, LAEFF campus, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain e-mail: palau@ieec.uab.es
² Departament d'Astronomia i Meteorologia (IEEC-UB), Institut de Ciències del Cosmos, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Academia Sinica, Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 106, Taiwan
⁵ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁶ Max-Planck-Institut for Astronomy, Knigstuhl 17, 69117 Heidelberg, Germany

Received: 31 August 2009
Accepted: 10 November 2009

Abstract

Aims. Our main aim is to study the influence of the initial conditions of a cloud in the intermediate/high-mass star formation process.

Methods. We observed with the VLA, PdBI, and SMA the centimeter and millimeter continuum, N₂H⁺ (1–0), and CO (2–1) emission associated with a dusty cloud harboring a nascent cluster with intermediate-mass protostars.

Results. At centimeter wavelengths we found a strong source, tracing a UC region, at the eastern edge of the dusty cloud, with a shell-like structure, and with the near-infrared counterpart falling in the center of the shell. This is presumably the most massive source of the forming cluster. About 15'' to the west of the UC region and well embedded in the dusty cloud, we detected a strong millimeter source, MM1, associated with centimeter and near-infrared emission. MM1 seems to be driving a prominent high-velocity CO bipolar outflow elongated in the northeast-southwest direction, and is embedded in a ridge of dense gas traced by N₂H⁺, elongated roughly in the same direction as the outflow. We estimated that MM1 is an intermediate-mass source in the Class 0/I phase. 
 About 15'' to the south of MM1, and still more deeply embedded in the dusty cloud, we detected a compact millimeter source, MM2, with neither centimeter 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 we found signposts of infall motions. MM2, being deeply embedded within the dusty cloud, with an associated water maser but no hints of CO outflow emission, is an intriguing object, presumably of intermediate mass.

Conclusions. The UC region is found at the border of a dusty cloud which is currently undergoing active star formation. Two intermediate-mass protostars in the dusty cloud seem to have formed after the UC region and have different properties related to the outflow phenomenon. Thus, a single cloud with similar dust emission and similar dense gas column densities seems to be forming objects with different properties, suggesting that the initial conditions in the cloud are not determining all the star formation process.