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How do methanol masers manage to appear in the youngest star vicinities and isolated molecular clumps?

Published online by Cambridge University Press:  01 March 2007

A. M. Sobolev ,
D. M. Cragg ,
S. P. Ellingsen ,
M. J. Gaylard ,
S. Goedhart ,
C. Henkel ,
M. S. Kirsanova ,
A. B. Ostrovskii ,
N. V. Pankratova  and
O. V. Shelemei
...Show all authors
A. M. Sobolev
Affiliation:
Ural State University, Ekaterinburg, 620083, Russia, email: Andrej.Sobolev@usu.ru
D. M. Cragg
Affiliation:
Monash University, Clayton, Australia, email: Dinah.Cragg@monash.edu.au
S. P. Ellingsen
Affiliation:
University of Tasmania, Hobart, Australia, email: Simon.Ellingsen@utas.edu.au
M. J. Gaylard
Affiliation:
Hartebeesthoek Radio Astronomy Observatory, South Africa, email: sharmila@hartrao.ac.za
S. Goedhart
Affiliation:
Hartebeesthoek Radio Astronomy Observatory, South Africa, email: sharmila@hartrao.ac.za
C. Henkel
Affiliation:
MPIfR, Bonn, Germany, email: p220hen@mpifr-bonn.mpg.de
M. S. Kirsanova
Affiliation:
Institute for Astronomy, Moscow, Russia, email: kirsanova@inasan.ru
A. B. Ostrovskii
Affiliation:
Ural State University, Ekaterinburg, 620083, Russia, email: Andrej.Sobolev@usu.ru
N. V. Pankratova
Affiliation:
Ural State University, Ekaterinburg, 620083, Russia, email: Andrej.Sobolev@usu.ru
O. V. Shelemei
Affiliation:
Ural State University, Ekaterinburg, 620083, Russia, email: Andrej.Sobolev@usu.ru
D. J. van der Walt
Affiliation:
North-West University, South Africa, email: johan.vanderwalt@nwu.ac.za
T. S. Vasyunina
Affiliation:
MPIA, Heidelberg, Germany, email: Vasyunin@mpia-hd.mpg.de
M. A. Voronkov
Affiliation:
ATNF CSIRO, Sydney, Australia, email: Maxim.Voronkov@csiro.au
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Abstract

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General characteristics of methanol (CH3OH) maser emission are summarized. It is shown that methanol maser sources are concentrated in the spiral arms. Most of the methanol maser sources from the Perseus arm are associated with embedded stellar clusters and a considerable portion is situated close to compact HII regions. Almost 1/3 of the Perseus Arm sources lie at the edges of optically identified HII regions which means that massive star formation in the Perseus Arm is to a great extent triggered by local phenomena. A multiline analysis of the methanol masers allows us to determine the physical parameters in the regions of maser formation. Maser modelling shows that class II methanol masers can be pumped by the radiation of the warm dust as well as by free-free emission of a hypercompact region (hcHII) with a turnover frequency exceeding 100 GHz. Methanol masers of both classes can reside in the vicinity of hcHIIs. Modelling shows that periodic changes of maser fluxes can be reproduced by variations of the dust temperature by a few percent which may be caused by variations in the brightness of the central young stellar object reflecting the character of the accretion process. Sensitive observations have shown that the masers with low flux densities can still have considerable amplification factors. The analysis of class I maser surveys allows us to identify four distinct regimes that differ by the series of their brightest lines.

Keywords

maserscatalogssurveysstars: formationISM: cloudsevolutionkinematics and dynamicsstructureGalaxy: structureradio lines: ISM
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S242: Astrophysical Masers and their Environments , March 2007 , pp. 81 - 88
Copyright
Copyright © International Astronomical Union 2008

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