A population of very young brown dwarfs and free-floating planets in Orion

We describe the results of a very deep imaging survey of the Trapezium cluster in the IJH bands, using the UKIRT high-resolution camera UFTI. Approximately 32 per cent of the 515 point sources detected are brown dwarf candidates, including several free-floating objects with masses below the deuterium-burning (planetary) threshold at 0.013 M_⊙, which are detectable because of their extreme youth. We have confidence that almost all the sources detected are cluster members, since foreground contamination is minimal in the 33-arcmin² area surveyed, and the dense backdrop of OMC-1 obscures all background stars at these wavelengths. Extinction is calculated from the ( J − H ) colours, permitting accurate luminosity estimates, and temperatures are derived from the dereddened ( I − J ) colours. There is some evidence for a cut-off in the luminosity function below the level corresponding to several Jupiter masses, which may represent the bottom end of the initial mass function . Since star formation is complete in the Trapezium, this limit could have wide significance, if confirmed. However, it could well be an effect of the dispersal of the molecular cloud by the central O-type stars, a process for which the time-scale will vary between star formation regions.     

A search for propylene oxide and glycine in Sagittarius B2 (LMH) and Orion

We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have been able to put sensitive upper limits on the abundances of both molecules. The 3σ upper limits derived for glycine conformer I are  3.7 × 10¹⁴ cm⁻²  in both Orion-KL and Sgr B2 (LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3σ upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of  7.7 × 10¹² cm⁻²  in both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results have ruled out the detection of glycine (both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of  3.0 × 10¹⁴ cm⁻²  in Orion-KL and  6.7 × 10¹⁴ cm⁻²  in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the interstellar medium, but have not been able to plausibly assign these transitions to any carrier.     

4.8 – 20 μm Imaging of orion BN/KL: II. A new look at luminosity sources and the role of IRc2

We have reconsidered the energetics of the BN/KL infrared complex, using array images at nine wavelengths between 4.8 and 20 m, and find a much lower luminosity for IRc2 than the generally accepted value. The new observations resolve larcsec structure throughout the region, including several new compact sources within a few arcsec of IRc2 and significant details imaged in the 9.7 m silicate feature. Together with other recent work, the results suggest that luminous stars associated with three compact HII regions found within BN/KL, rather than IRc2, may be the more significant luminosity sources for the complex.     

Primordial substructure in the Orion Nebula Cluster

We use numerical N -body simulations of the Orion Nebula Cluster (ONC) to investigate the possibility of substructure in its formation. There is no substructure apparent in the ONC today. However, unless there was a remarkable degree of homogeneity in the molecular cloud from which it formed, it seems unlikely that this would have been true of the cluster in its earliest phase. More plausibly, the early structure of the cluster would have consisted of groups or clumps of subclusters, following the structure of the cloud itself. We have explored the extent to which such subclusters could subsequently have merged, and find that the age of the cluster is a critical factor. The most inhomogeneous initial conditions, comprising a small number of subclusters with many members, are ruled out by an age of 2 Myr or less. There is a considerable amount of freedom in the other direction, however, which suggests that fragmentation in the original cloud is more likely to have been on the scale of small clumps, each producing fewer than 100 stars. These initial subclusters could have been very dense – perhaps two or three orders of magnitude more dense than the core of the ONC today.     

A near-infrared fabry-perot imager at CRL 1.5m telescope and the structure and velocity field of shocked H2 emission in orion KL region

We have developed a near-infrared Fabry-Perot imager at the Nasmyth focus of the Communications Research Laboratory (CRL) 1.5 m telescope at Tokyo. Using this wide field Fabry-Perot imager, we obtained continuum-subtracted images of the H₂ v=1–0 S(1) line for the Orion KL region.