Implications of a hot atmosphere/corino from ALMA observations towards
  NGC1333 IRAS 4A1
  We report high angular resolution observations of NGC1333 IRAS4A, a
protostellar binary including A1 and A2, at 0.84 mm with the Atacama Large
Millimeter/submillimeter Array. From the continuum observations, we suggest
that the dust emission from the A1 core is optically thick, and A2 is
predominantly optically thin. The A2 core, exhibiting a forest of spectral
lines including complex molecules, is a well known hot corino as suggested by
previous works. More importantly, we report, for the first time, the solid
evidence of complex organic molecules (COMs), including CH3OH, ^13CH3OH,
CH2DOH, CH3CHO associated with the A1 core seen in absorption. The absorption
features mostly arise from a compact region around the continuum peak position
of the A1 core. Rather than originating from a larger common envelope
surrounding the protobinary, the COM features are associated with individual
cores A1 and A2. Considering the signatures observed in both continuum and
spectral lines, we propose two possible scenarios for IRAS 4A1 - the COM
absorption lines may arise from a hot-corino-like atmosphere at the surface of
an optically-thick circumstellar disk around A1, or the absorption may arise
from different layers of a temperature-stratified dense envelope.
