Young stars and protostellar cores near NGC?2023

摘要

Context. We investigate the young (proto)stellar population in NGC2023 and the L1630 molecular cloud bordering the HIIregion IC434, using Spitzer IRAC and MIPS archive data, JCMTSCUBA imaging and spectroscopy as well as targeted BIMA observations ofone of the Class0 protostars, NGC2023 MM1. Aims. We study the distribution of gas, dust and young stars inthis region to see where stars are forming, whether the expansion ofthe HII region has triggered star formation, and whether dense cold cores have already formed stars. Methods. We have performed photometry of all IRAC and MIPSimages, and used color-color diagrams to identify and classify allyoung stars seen within a field along the boundary between IC434 and L1630. For somestars, which have sufficient optical, IR, and/or sub-millimeter data wehave also used the onlineSED fitting tool for a large2Darchive of axisymmetric radiative transfer models to performmore detailed modeling of the observed SEDs. We identify5sub-millimeter cores in our 850 and 450mSCUBA images, two of which have embedded class0 orIprotostars. Observations with BIMA are used to refine theposition and characteristics of the Class0 sourceNGC2023MM1. These observations show that it isembedded in a very cold cloud core, which is strongly enhanced in NH2D. Results. We find that HD37903 is the most massive memberof a cluster with 20-30PMS stars. We also find smaller groups ofPMS stars formed from the Horsehead nebula and another elephant trunkstructure to the north of the Horsehead. Star formation is alsooccurring in the dark lane seen in IRAC images and in thesub-millimeter continuum. We refine the spectral classification ofHD37903 to B2Ve. We find that the star has a clearIRexcess, and therefore it is a young Herbig Bestar. Conclusions. Our study shows that the expansion of the IC434 HIIregion has triggered star formation in some of the dense elephant trunkstructures and compressed gas inside the L1630 molecular cloud.This pre-shock region is seen as a sub-millimeter ridge in which starshave already formed. The cluster associated with NGC2023 is veryyoung, and has a large fraction of ClassI sources. Key words: dust, extinction - ISM: clouds - infrared: ISM