Chemistry of massive young stellar objects with a disk-like structure
  Our goal is to take an inventory of complex molecules in three well-known
high-mass protostars for which disks or toroids have been claimed and to study
the similarities and differences with a sample of massive YSOs without evidence
of such flattened disk-like structures. With a disk-like geometry, UV radiation
can escape more readily and potentially affect the ice and gas chemistry on
hot-core scales. A partial submillimeter line survey, targeting CH3OH, H2CO,
C2H5OH, HCOOCH3, CH3OCH3, CH3CN, HNCO, NH2CHO, C2H5CN, CH2CO, HCOOH, CH3CHO,
and CH3CCH, was made toward three massive YSOs with disk-like structures,
IRAS20126+4104, IRAS18089-1732, and G31.41+0.31. Rotation temperatures and
column densities were determined by the rotation diagram method, as well as by
independent spectral modeling. The molecular abundances were compared with
previous observations of massive YSOs without evidence of any disk structure,
targeting the same molecules with the same settings and using the same analysis
method. Consistent with previous studies, different complex organic species
have different characteristic rotation temperatures and can be classified
either as warm (>100 K) or cold (<100 K). The excitation temperatures and
abundance ratios are similar from source to source and no significant
difference can be established between the two source types. Acetone, CH3COCH3,
is detected for the first time in G31.41+0.31 and IRAS18089-1732. Temperatures
and abundances derived from the two analysis methods generally agree within
factors of a few. The lack of chemical differentiation between massive YSOs
with and without observed disks suggest either that the chemical complexity is
already fully established in the ices in the cold prestellar phase or that the
material experiences similar physi- cal conditions and UV exposure through
outflow cavities during the short embedded lifetime.
