A dense micro-cluster of Class 0 protostars in NGC 2264 D-MM1

We present sensitive and high angular resolution (~1") 1.3 mm continuum observations of the dusty core D-MM1 in the Spokes cluster in NGC 2264 using the Submillimeter Array. A dense micro-cluster of seven Class 0 sources was detected in a 20" x 20" region with masses between 0.4 to 1.2 solar masses and deconvolved sizes of about 600 AU. We interpret the 1.3 mm emission as arising from the envelopes of the Class 0 protostellar sources. The mean separation of the 11 known sources (SMA Class 0 and previously known infrared sources) within D-MM1 is considerably smaller than the characteristic spacing between sources in the larger Spokes cluster and is consistent with hierarchical thermal fragmentation of the dense molecular gas in this region.Comment: Accepted for publication in the Astrophysical Journal Letter

A contracting circumbinary molecular ring with an inner cavity of about 140 AU around Ori 139-409

Sensitive and subarcsecond resolution ($\sim$ 0.7\arcsec) CH$_3$OH(7$_{-2,6}$ $\to$ 6$_{-2,5}$) line and 890 $\mu$m continuum observations made with the Submillimeter Array (SMA) towards the hot molecular circumbinary ring associated with the young multiple star Ori 139-409 are presented. The CH$_3$OH(7$_{-2,6}$ - 6$_{-2,5}$) emission from the ring is well resolved at this angular resolution revealing an inner cavity with a size of about 140 AU. A LTE model of a Keplerian disk with an inner cavity of the same size confirms the presence of this cavity. Additionally, this model suggests that the circumbinary ring is contracting with a velocity of V$_{inf}$ $\sim$ 1.5 km s$^{-1}$ toward the binary central compact circumstellar disks reported at a wavelength of 7 mm. {\bf The inner central cavity seems to be formed by the tidal effects of the young stars in the middle of the ring.} The ring appears to be not a stationary object. Furthermore, the infall velocity we determine is about a factor of 3 slower than the free-fall velocity corresponding to the dynamical mass. This would correspond to a mass accretion rate of about 10$^{-5}$ M$_\odot$/yr. We found that the dust emission associated with Ori 139-409 appears to be arising from the circumstellar disks with no strong contribution from the molecular gas ring. A simple comparison with other classical molecular dusty rings (e.g. GG Tau, UZ Tau, and UY Aur) suggests that Ori 139-409 could be one of the youngest circumbinary rings reported up to date. Finally, our results confirm that the circumbinary rings are actively funneling fresh gas material to the central compact binary circumstellar disks, i.e. to the protostars in the very early phases of their evolution.Comment: Accepted by MNRA

Explosive Disintegration of a Massive Young Stellar System in Orion

Young massive stars in the center of crowded star clusters are expected to undergo close dynamical encounters that could lead to energetic, explosive events. However, there has so far never been clear observational evidence of such a remarkable phenomenon. We here report new interferometric observations made with the Submillimeter Array (SMA) that indicate the well known enigmatic wide-angle outflow located in the Orion BN/KL star-forming region to have been produced by such a violent explosion during the disruption of a massive young stellar system, and that this was caused by a close dynamical interaction about 500 years ago. This outflow thus belongs to a totally different family of molecular flows which is not related to the classical bipolar flows that are generated by stars during their formation process. Our molecular data allow us to create a 3D view of the debris flow and to link this directly to the well known Orion H$_2$ "fingers" farther outComment: Accepted by ApJ Letters The 3D movie can be found in: ftp://ftp.mpifr-bonn.mpg.de/outgoing/lzapata/movie.gi