Deep JHKs and Spitzer Imaging of Four Isolated Molecular Cloud Cores
  We present observations in eight wavebands from 1.25-24 microns of four dense
cores: L204C-2, L1152, L1155C-2, and L1228. Our goals are to study the YSO
population of these cores and to measure the mid-infrared extinction law. With
our combined near-infrared and Spitzer photometry, we classify each source in
the cores as, among other things, background stars, galaxies, or embedded young
stellar objects (YSOs). L1152 contains three YSOs and L1228 has seven, but
neither L204C-2 nor L1155C-2 appear to contain any YSOs. We estimate an upper
limit of 7x10^-5 to 5x10^-4 solar luminosities for any undiscovered YSOs in our
cores. We also compute the line-of-sight extinction law towards each background
star. These measurements are averaged spatially, to create chi-squared maps of
the changes in the mid-infrared extinction law throughout our cores, and also
in different ranges of extinction. From the chi-squared maps we identify two
small regions in L1152 and L1228 where the outflows in those cores appear to be
destroying the larger dust grains, thus altering the extinction law in those
regions. On average, however, our extinction law is relatively flat from 3.6 to
24 microns for all ranges of extinction and in all four cores. From 3.6 to 8
microns this law is consistent with a dust model that includes larger dust
grains than the diffuse interstellar medium, which suggests grain growth has
occurred in our cores. At 24 microns, our extinction law is 2-4 times higher
than predicted by dust models. However, it is similar to other empirical
measurements.
