Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mnras.331..521c&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 331, Issue 2, pp. 521-536.
Astronomy and Astrophysics
Astronomy
66
Masers, Hii Regions, Ism: Molecules, Radio Lines: Ism
Scientific paper
Class II methanol masers are found in close association with OH main-line masers in many star-forming regions, where both are believed to flag the early stages in the evolution of a massive star. We have studied the formation of masers in methanol and OH under identical model conditions for the first time. Infrared pumping by radiation from warm dust at temperatures >100K can account for the known maser lines in both molecules, many of which develop simultaneously under a range of conditions. The masers form most readily in cooler gas (<100K) of moderately high density (105-108cm-3), although higher gas temperatures and/or lower densities are also compatible with maser action. The agreement between the current model (developed for methanol) and the established OH maser trends is very encouraging, and we anticipate that further tuning of the model will further improve such agreement. We find the gas-phase molecular abundance to be the key determinant of observable maser activity for both molecules. Sources exhibiting both 6668-MHz methanol and 1665-MHz OH masers have a typical flux density ratio of 16; our model suggests that this may be a consequence of maser saturation. We find that the 1665-MHz maser approaches the saturated limit for OH abundances >10-7.3, while the 6668-MHz maser requires a greater methanol abundance >10-6. OH-favoured sources are likely to be less abundant in methanol, while methanol-favoured sources may be less abundant in OH or experiencing warm (>125K), dense (~107cm-3) conditions. These abundance requirements offer the possibility of tying the appearance of masers to the age of the new-born star via models of gas-phase chemical evolution following the evaporation of icy grain mantles.
Cragg Dinah M.
Godfrey Peter D.
Sobolev Andrej M.
No associations
LandOfFree
Modelling methanol and hydroxyl masers in star-forming regions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Modelling methanol and hydroxyl masers in star-forming regions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modelling methanol and hydroxyl masers in star-forming regions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1489951