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Astron. Astrophys. 362, 723-729 (2000)


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On the occurrence of the 6.7 GHz CH3OH maser emission in UCH II regions

C. Codella 1,2 and L. Moscadelli 3

1 Istituto di Fisica dello Spazio Interplanetario, CNR, Area di Ricerca Tor Vergata, Via Fosso del Cavaliere 100, 00133 Roma, Italy
2 Observatorio Astronómico Nacional (IGN), Apartado 1143, 28800 Alcalá de Henares (Madrid), Spain
3 Stazione Astronomica di Cagliari, Loc. Poggio dei Pini, 09012 Capoterra (Cagliari), Italy

Received 21 April 2000 / Accepted 30 August 2000

Abstract

We present the results of a statistical survey of the 6.7 GHz CH3OH and 22.2 GHz H2O emissions towards a large homogeneous sample of ultracompact (UC) H II regions, performed to investigate the nature of the methanol emission: does it point out ionized regions or does it trace earlier stages of the star forming process?

The present detection rates are almost identical: 23% for CH3OH and 22% for H2O. Even considered the uncertainties of the survey, the large number of non-detections is consistent with the scenario where methanol masers disappear during the UC phase, like water masers do. Moreover, the probability to have the CH3OH counterpart of a H2O source is at least 40%, indicating that these maser emissions are emphasizing two at least partly overlapping evolutionary phases. The comparison between the velocity ranges suggests that methanol and water masers form in different gas components related to the star forming process.

Key words: ISM: clouds – ISM: H ii regions – ISM: molecules – radio lines: ISM

Send offprint requests to: C. Codella (codella@ifsi.rm.cnr.it)

© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000

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