Toward understanding the formation of multiple systems. A pilot IRAM-PdBI survey of Class 0 objects
Abstract
Context. The formation process of binary stars and multiple systems is poorly understood. The multiplicity rate of Class II pre-main-sequence stars and Class I protostars is well documented and known to be high (~ 30% to 50% between ~100 and 4000 AU). However, optical / near-infrared observations of Class I/Class II YSOs barely constrain the pristine properties of multiple systems, since dynamical evolution can quickly alter these properties during the protostellar phase.
Aims: Here, we seek to determine the typical outcome of protostellar collapse and to constrain models of binary formation by core fragmentation during collapse, using high-resolution millimeter continuum imaging of very young (Class 0) protostars observed at the beginning of the main accretion phase.
Methods: We carried out a pilot high-resolution study of 5 Class 0 objects, including 3 Taurus sources and 2 Perseus sources, using the most extended (A) configuration of the IRAM Plateau de Bure Interferometer (PdBI) at 1.3 mm. Our PdBI observations have a typical HPBW resolution ~0.3´´-0.5´´ and rms continuum sensitivity ~0.1-1 mJy/beam, which allow us to probe the multiplicity of Class 0 protostars down to separations a ∼50 AU and circumstellar mass ratios q ∼0.07.
Results: We detected all 5 primary Class 0 sources in the 1.3 mm dust continuum. A single component associated with the primary Class 0 object was detected in the case of the three Taurus sources, while robust evidence of secondary components was found toward the two Perseus sources: L1448-C and NGC1333-IR2A. We show that the secondary 1.3 mm continuum component detected ~600 AU south-east of L1448-C, at a position angle close to that of the CO(2-1) jet axis traced by our data, is an outflow feature directly associated with the powerful jet driven by L1448-C. The secondary 1.3 mm continuum component detected ~1900 AU south-east of NGC1333-IR2A may either be a genuine protostellar companion or trace the edge of an outflow cavity. Therefore, our PdBI observations revealed only wide (>1500 AU) protobinary systems and/or outflow-generated features.
Conclusions: When combined with previous millimeter interferometric observations of Class 0 protostars, our pilot PdBI study tentatively suggests that the binary fraction in the ~75-1000 AU range increases from the Class 0 to the Class I stage. It also seems to argue against purely hydrodynamic models of binary star formation. We briefly discuss possible alternative scenarios to reconcile the low multiplicity rate of Class 0 protostars on small scales with the higher binary fraction observed at later (e.g. Class I) evolutionary stages.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- March 2010
- DOI:
- 10.1051/0004-6361/200913492
- arXiv:
- arXiv:1001.3691
- Bibcode:
- 2010A&A...512A..40M
- Keywords:
-
- stars: formation;
- binaries: general;
- ISM: clouds;
- ISM: jets and outflows;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in Astronomy and Astrophysics. Abstract has been shortened