Infrared [ITAL]L[/ITAL]-Band Observations of the Trapezium Cluster: A Census of Circumstellar Disks and Candidate Protostars

Abstract

We report the results of a sensitive near-infrared JHKL imaging survey of the Trapezium cluster in Orion. We use the JHKL colors to obtain a census of infrared excess stars in the cluster. Of (391) stars brighter than 12th magnitude in the K and L bands, 80%^7% are found to exhibit detectable infrared excess on the J[H, K[L color-color diagram. Examination of a subsample of 285 of these stars with published spectral types yields a slightly higher infrared excess fraction of 85%. We Ðnd that 97% of the optical proplyds in the cluster exhibit excess in the JHKL color-color diagram indicating that the most likely origin of the observed infrared excesses is from circumstellar disks. We interpret these results to indicate that the fraction of stars in the cluster with circumstellar disks is between 80%È85%, conÐrming earlier published suggestions of a high disk fraction for this young cluster. Moreover, we Ðnd that the probability of Ðnding an infrared excess around a star is independent of stellar mass over essentially the entire range of the stellar mass function down to the hydrogen burning limit. Consequently, the vast majority of stars in the Trapezium cluster appear to have been born with circumstellar disks and the potential to subsequently form planetary systems, despite formation within the environment of a rich and dense stellar cluster. We identify 78 stars in our sample characterized by K[L colors suggestive of deeply embedded objects. The spatial distribution of these objects di †ers from that of the rest of the cluster members and is similar to that of the dense molecular cloud ridge behind the cluster. About half of these objects are detected in the short wavelength (J and H) bands, and these are found to be characterized by extreme infrared excess. This suggests that many of these sources could be protostellar in nature. If even a modest fraction (i.e., D50%) of these objects are protostars, then star formation could be continuing in the molecular ridge at a rate comparable to that which produced the foreground Trapezium cluster.

Silicon Monoxide Observations Reveal a Cluster of Hidden Compact Outflows in the OMC 1 South Region

“…1). We note that the source 137-408 does not have centimeter or infrared counterparts (see Lada et al 2000Lada et al , 2004Smith et al 2004;Robberto et al 2005;Zapata et al 2004aZapata et al , 2004b, possibly because it is a genuine embedded Class 0 object. We propose that 137-408 is likely the exciting source of the outflow.…”

“…A few sources have been proposed to power the HH 529 object: the infrared source TCC 009 ( Smith et al (2004). Possibly, the best candidate for the exciting source of this bow shock is the object TPSC-1 ( Lada et al 2000), which is seen only in the L band. We have indicated the position and motion of this HH object in Figure 4.…”

“…1), a source with no counterpart at infrared wavelengths (see Lada et al 2000Lada et al , 2004Muench et al 2002;Smith et al 2004;Robberto et al 2005), perhaps suggesting that it could be associated with a Class 0 protostar. We propose that the object 137-347 is possibly its exciting source.…”

Commission 37: Star Clusters and Associations: (Amas Stellaires Et Associations)

“…The rotation increase is consistent with the existence of a central dark mass concentration equal to 2500 MQ. Lada et al (2000) report the results of a sensitive near-infrared JHKL imaging survey of the Trapezium cluster in Orion. They use the JHKL colors to obtain a census of infrared excess stars in the cluster.…”

H2 Mid-IR Pure Rotational Emission from Young Stars: The TEXES/IRTF Survey

“…While great progress has been made in the study of circumstellar dust at both near-infrared (e.g. [2]) and millimeter wavelengths (e.g. [3]).…”