Young Stars and Protostellar Cores near NGC 2023
  We investigate the young (proto)stellar population in NGC 2023 and the L 1630
molecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPS
archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA
observations of one of the Class 0 protostars, NGC 2023 MM1. We have performed
photometry of all IRAC and MIPS images, and used color-color diagrams to
identify and classify all young stars seen within a 22'x26' field along the
boundary between IC 434 and L 1630. For some stars, which have sufficient
optical, IR, and/or sub-millimeter data we have also used the online SED
fitting tool for a large 2D archive of axisymmetric radiative transfer models
to perform more detailed modeling of the observed SEDs. We identify 5
sub-millimeter cores in our 850 and 450 micron SCUBA images, two of which have
embedded class 0 or I protostars. Observations with BIMA are used to refine the
position and characteristics of the Class 0 source NGC 2023 MM 1. These
observations show that it is embedded in a very cold cloud core, which is
strongly enhanced in NH2D. We find that HD 37903 is the most massive member of
a cluster with 20 -- 30 PMS stars. We also find smaller groups of PMS stars
formed from the Horsehead nebula and another elephant trunk structure to the
north of the Horsehead. We refine the spectral classification of HD 37903 to B2
Ve. Our study shows that the expansion of the IC 434 HII region has triggered
star formation in some of the dense elephant trunk structures and compressed
gas inside the L 1630 molecular cloud. This pre-shock region is seen as a
sub-millimeter ridge in which stars have already formed. The cluster associated
with NGC 2023 is very young, and has a large fraction of Class I sources.
