Herschel observations of B1-bS and B1-bN: two first hydrostatic core
  candidates in the Perseus star-forming cloud
  We report far-IR Herschel observations obtained between 70 $\mu$m and 500
$\mu$m of two star-forming dusty condensations, B1-bS and B1-bN, in the B1
region of the Perseus star-forming cloud. In the Western part of the Perseus
cloud, B1-bS is the only source detected in all of the 6 PACS and SPIRE
photometric bands without being visible in the Spitzer map at 24 $\mu$m. B1-bN
is clearly detected between 100 $\mu$m and 250 $\mu$m. We have fitted the
spectral energy distributions of these sources to derive their physical
properties, and find that a simple greybody model fails to reproduce the
observed SEDs. At least a two-component model, consisting of a central source
surrounded by a dusty envelope is required. The properties derived from the
fit, however, suggest that the central source is not a Class 0 object. We then
conclude that while B1-bS and B1-bN appear to be more evolved than a
pre-stellar core, the best-fit models suggest that their central objects are
younger than a Class 0 source. Hence, they may be good candidates to be
examples of the first hydrostatic core phase. The projected distance between
B1-bS and B1-bN is a few Jeans lengths. If their physical separation is close
to this value, this pair would allow the mutual interactions between two
forming stars at a very early stage of their evolution to be studied.
