Hyperfine structure of the methanol molecule as traced by Class I methanol masers
Journal article, 2024
We present results on simultaneous observations of Class I methanol masers at 25, 36, and 44 GHz towards 22 Galactic targets carried out with the Effelsberg 100-m telescope. The study investigates relations between the hyperfine (HF) structure of the torsion–rotation transitions in CH3OH and maser activity. By analysing the radial velocity shifts between different maser lines together with the patterns of the HF structure based on laboratory measurements and quantum-chemical calculations, we find that in any source only one specific HF transition forms the maser emission and that this transition changes from source to source. The physical conditions leading to this selective behaviour are still unclear. Using accurate laboratory rest frequencies for the 25 GHz transitions, we have refined the centre frequencies for the HF multiplets at 36, 44, and 95 GHz: f36 = (36169.2488 ± 0.0002stat ± 0.0004sys) MHz. f44 = (44069.4176 ± 0.0002stat ± 0.0004sys) MHz, and f95 = (95169.4414 ± 0.0003stat ± 0.0004sys) MHz. Comparison with previous observations of 44 GHz masers performed 6–10 yr ago with a Korean 21-m Korean Very Long Baseline Interferometry Network telescope towards the same targets confirms the kinematic stability of Class I maser line profiles during this time interval and reveals a systematic radial velocity shift of 0.013 ± 0.005 km s−1 between the two telescopes.
techniques: spectroscopic
methods: numerical
elementary particles
radio lines: ISM
ISM: molecules
Author
I. I. Agafonova
Russian Academy of Sciences
O. S. Bayandina
Arcetri Astrophysical Observatory
Y. Gong
Max Planck Society
Chinese Academy of Sciences
C. Henkel
Max Planck Society
Chinese Academy of Sciences
Kee-Tae Kim
University of Science and Technology (UST)
Korea Astronomy and Space Science Institute
M. G. Kozlov
Saint Petersburg Electrotechnical University
Petersburg Nuclear Physics Institute (PNPI)
Boy Lankhaar
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
S. A. Levshakov
Russian Academy of Sciences
K. Menten
Max Planck Society
W. Ubachs
Vrije Universiteit Amsterdam
I. E. Val'tts
Russian Academy of Sciences
W. Yang
Max Planck Society
Nanjing University
Monthly Notices of the Royal Astronomical Society
00358711 (ISSN) 13652966 (eISSN)
Vol. 533 2 1714-1732Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1093/mnras/stae1815