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Abstract: We investigate the young protostellar population in NGC 2023 and the L 1630molecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPSarchive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMAobservations of one of the Class 0 protostars, NGC 2023 MM1. We have performedphotometry of all IRAC and MIPS images, and used color-color diagrams toidentify and classify all young stars seen within a 22-x26- field along theboundary between IC 434 and L 1630. For some stars, which have sufficientoptical, IR, and-or sub-millimeter data we have also used the online SEDfitting tool for a large 2D archive of axisymmetric radiative transfer modelsto perform more detailed modeling of the observed SEDs. We identify 5sub-millimeter cores in our 850 and 450 micron SCUBA images, two of which haveembedded class 0 or I protostars. Observations with BIMA are used to refine theposition and characteristics of the Class 0 source NGC 2023 MM 1. Theseobservations show that it is embedded in a very cold cloud core, which isstrongly enhanced in NH2D. We find that HD 37903 is the most massive member ofa cluster with 20 - 30 PMS stars. We also find smaller groups of PMS starsformed from the Horsehead nebula and another elephant trunk structure to thenorth of the Horsehead. We refine the spectral classification of HD 37903 to B2Ve. Our study shows that the expansion of the IC 434 HII region has triggeredstar formation in some of the dense elephant trunk structures and compressedgas inside the L 1630 molecular cloud. This pre-shock region is seen as asub-millimeter ridge in which stars have already formed. The cluster associatedwith NGC 2023 is very young, and has a large fraction of Class I sources.

Author: B. Mookerjea TIFR, India, G. Sandell SOFIA-Usra, T. H. Jarrett SSC, Caltech, J. P. McMullin ALMA, Chile and Nrao


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