Chemistry of massive young stellar objects with a disk-like structure ^⋆

¹ Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: isokoski@strw.leidenuniv.nl
² Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
³ CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Max-Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany

Received: 19 December 2012
Accepted: 21 March 2013

Abstract

Aims. 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 young stellar objects (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.

Methods. 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, IRAS 20126+4104, IRAS 18089-1732, 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.

Results. 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 IRAS 18089-1732. Temperatures and abundances derived from the two analysis methods generally agree within factors of a few.

Conclusions. 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 physical conditions and UV exposure through outflow cavities during the short embedded lifetime.