Models of class II methanol masers based on improved molecular data

By D. M. Cragg, A. Sobolev, P. Godfrey. 2005

218 citations recorded by the source corpus.

The class II masers of methanol are associated with the early stages of formation of high-mass stars. Modelling of these dense, dusty environments has demonstrated that pumping by infrared radiation can account for the observed masers. Collisions with other molecules in the ambient gas also play a significant role, but have not been well modelled in the past. Here we examine the effects on the maser models of newly available collision rate coefficients for methanol. The new collision data do not alter which transitions become masers in the models, but do influence their brightness and the conditions under which they switch on and off. At gas temperatures above 100 K the effects are broadly consistent with a reduction in the overall collision cross-section. This means, for example, that a slightly higher gas density than identified previously can account for most of the observed masers in W3(OH). We have also examined the effects of including more excited-state energy levels in the models, and find that these play a significant role only at dust temperatures above 300 K. An updated list of class II methanol maser candidates is presented.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/ac5ae60a395fa958cd94283ac5ea20b6575c444b

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In Astronomy and Astrophysics

1. M. Povich
2. B. Whitney
3. R. Indebetouw
4. E. Churchwell
5. Italy.
6. Chile.
7. M. Meade
8. C. Cyganowski

In Atomic and Molecular Physics, and Optics

1. R. Indebetouw
2. B. Whitney

In Spectroscopy

1. R. Indebetouw
2. B. Whitney

Citations in the corpus

• A CLASS I AND CLASS II CH3OH MASER SURVEY OF EGOs FROM THE GLIMPSE SURVEY (2009, background): “Class II 6.7 GHz CH 3 OH masers, radiatively pumped by IR emission from warm dust (Cragg et al. 1992, 2005, and references therein), are associated exclusively with massive YSOs (e.g. Minier et al. 2003).”
• A CATALOG OF EXTENDED GREEN OBJECTS IN THE GLIMPSE SURVEY: A NEW SAMPLE OF MASSIVE YOUNG STELLAR OBJECT OUTFLOW CANDIDATES (2008, background): “These masers are radiatively pumped by IR photons emitted by warm dust in massive star-forming regions (e.g. Cragg et al. 2005, and references therein), and are thought to trace both the inner parts – 9 – of outflows and disks (c.f. De Buizer 2003).”
• Accretion disks in luminous young stellar objects (2015, background): “The masers are not seen in the inner disk because the local temperature or density probably exceed the upper excitation limits of 250 K and 109 cm−3, values predicted by the model calculations of Cragg et al. (2005).”