Looking into the cradle: new mid-IR observations of multiple proto-stars^*

¹ Observatório Astronómico de Lisboa, Ed. Leste, Tapada da Ajuda, 1349-018 Lisboa, Portugal e-mail: nhuelamo@aol.ul.pt
² European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
³ Centro de Geofisica de Évora, Rua Romão Ramalho 59, 7002-554 Évora, Portugal
⁴ Observatoire de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland
⁵ Departamento de Astronomía, Universidad de Chile, Casilla Postal 36D, Santiago, Chile

Received: 3 September 2006
Accepted: 22 November 2006

Abstract

Context.The multiplicity rate of the youngest stellar objects is directly linked to their formation process, and therefore represents one of the most critical parameters to constrain theories of star formation. Multiplicities of embedded protostars are, however, not well determined empirically.

Aims.The aim of this work is to study the multiplicity of three embedded proto-stellar systems, namely SSV 63, L1551 NE, and L1551–IRS5, through mid-IR imaging. All of them are suspected binary or multiple systems, but prone to ambiguities in the literature.

Methods.We present high spatial resolution mid-infrared observations obtained with VISIR at the VLT.

Results.For the SSV 63 system, we report the discovery of a new Class I companion, approx 26 N of SSV63 E, which was never seen in previous near-IR and radio continuum studies. The companion to SSV 63 W, which was detected at near-IR wavelengths, is also present in the mid-IR regime. In the case of L1551 NE, we have confirmed the presence of a companion at 05 NW from the central star, as previously reported by Reipurth et al. (2002, AJ, 124, 1045). Finally, we have not detected any companion to L1551–IRS5. However, we find signs of extended emission around the target. In total, we have detected three binaries. The SEDs of the primaries are consistent with their Class I/flat-spectrum classification. For the secondaries, ancillary data are required to derive their evolutionary status.

Conclusions.The geometrical arrangement of sources in the SSV63 system strongly supports the view of hierarchical fragmentation of cloud cores.