ALMA Observations of Orion Source I at 350 and 660 GHz
  Orion Source I (`SrcI') is the protostar at the center of the Kleinmann-Low
Nebula. ALMA observations of SrcI with 0.2" angular resolution were made at 350
and 660 GHz to search for the H26alpha and H21alpha hydrogen recombination
lines and to measure the continuum flux densities. The recombination lines were
not detected, ruling out the possibility that SrcI is a hypercompact HII
region. The deconvolved size of the continuum source is approximately 0.23 x
0.07" (100 x 30 AU); it is interpreted as a disk viewed almost edge-on.
Optically thick thermal emission from ~500 K dust is the most plausible source
of the continuum, even at frequencies as low as 43 GHz; the disk mass is most
likely in the range 0.02 to 0.2 Mo. A rich spectrum of molecular lines is
detected, mostly from sulfur- and silicon-rich molecules like SO, SO2, and SiS,
but also including vibrationally excited CO and several unidentified
transitions. Lines with upper energy levels E_U > 500 K appear in emission and
are symmetric about the source's LSR velocity of 5 km/sec, while lines with E_U
< 500 K appear as blueshifted absorption features against the continuum,
indicating that they originate in outflowing gas. The emission lines exhibit a
velocity gradient along the major axis of the disk that is consistent with
rotation around a 5-7 Mo central object. The relatively low mass of SrcI and
the existence of a 100 AU disk around it are difficult to reconcile with the
model in which SrcI and the nearby Becklin-Neugebauer Object were ejected from
a multiple system 500 years ago.
