The methanol lines and hot core of OMC2-FIR4, an intermediate-mass
  protostar, with Herschel-HIFI
  In contrast with numerous studies on the physical and chemical structure of
low- and high-mass protostars, much less is known about their intermediate-mass
counterparts, a class of objects that could help to elucidate the mechanisms of
star formation on both ends of the mass range. We present the first results
from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4,
obtained in the CHESS (Chemical HErschel SurveyS of star forming regions) key
programme. The more than 100 methanol lines detected between 554 and 961 GHz
cover a range in upper level energy of 40 to 540 K. Our physical interpretation
focusses on the hot core, but likely the cold envelope and shocked regions also
play a role in reality, because an analysis of the line profiles suggests the
presence of multiple emission components. An upper limit of 10^-6 is placed on
the methanol abundance in the hot core, using a population diagram, large-scale
source model and other considerations. This value is consistent with abundances
previously seen in low-mass hot cores. Furthermore, the highest energy lines at
the highest frequencies display asymmetric profiles, which may arise from
infall around the hot core.
