Open AccessClass II maser candidates in substituted methanol: CH 3 OD, 13 CH 3 OH, CH 3 18 OH and CH 3 SH
Author(s) -
Johns K. P.,
Cragg D. M.,
Godfrey P. D.,
Sobolev A. M.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01982.x
Subject(s) - maser , physics , astrophysics , methanol , star formation , excited state , brightness , dipole , protostar , astronomy , galaxy , atomic physics , chemistry , quantum mechanics , organic chemistry
We investigate the possibility of interstellar masers in transitions of the methanol isotopomers CH 3 OD, 13 CH 3 OH and CH 3 18 OH, and of CH 3 SH. The model used, in which masers are pumped through the first and second torsionally excited states by IR radiation, has accounted successfully for the Class II masers in main species methanol, 12 CH 3 16 OH. Several potential maser candidates are identified for CH 3 OD, their detectability depending on the enrichment of this species in star‐forming regions. In 13 CH 3 OH and CH 3 18 OH the best maser candidates are direct counterparts of the well‐known 6.7‐ and 12.2‐GHz methanol masers, but the lower interstellar abundance of these substituted species means that the expected brightness is greatly reduced. The maser candidates in CH 3 SH are also weak. By comparing these species we find that the large b ‐component of the dipole moment in methanol plays a significant role in its propensity to form masers, as does the strong torsion–rotation interaction due to the light hydroxyl frame. Thus the exceptional brightness of interstellar methanol masers is due to a favourable combination of molecular properties as well as high interstellar abundance.