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Astron. Astrophys. 331, 317-327 (1998)

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Excitation of far-infrared lines of OH and maser pumping efficiency in circumstellar envelopes

Thai-Q-Tung * 1, Dinh-V-Trung 1, Nguyen-Q-Rieu 1, V. Bujarrabal 2, T. Le Bertre 1 and E. Gérard 3

1 Observatoire de Paris, DEMIRM, 61 Avenue de l'Observatoire, F-75014 Paris, France
2 Centro Astronómico de Yebes (IGN), Apartado 148, E-19080 Guadalajara, Spain
3 Observatoire de Paris-Meudon, Arpèges, Place J. Janssen, F-92195 Meudon Cedex, France

Received 28 July 1997 / Accepted 7 October 1997


We present the results obtained with a radiative transfer model to investigate the excitation of OH molecules. Fluxes of far-infrared rotational lines of OH are calculated in terms of a radiatively excited envelope and of a radiative transfer model including collisional and radiative excitation. The agreement with the OH far-infrared lines observed with ISO is satisfactory. The [FORMULA] line is found to be in absorption as observed. We also predict that the [FORMULA] line should be seen in absorption and also contributes to the maser pumping process. Maser pumping efficiencies are estimated from the model and compared to the values determined from recent OH far-infrared observations with ISO and OH maser data.

Key words: masers – radiative transfer – stars: circumstellar matter – stars: individual: IRC+10420

* on leave from Institute of Laser Technology, Hanoi, Vietnam

Send offprint requests to: Dinh-V-Trung

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© European Southern Observatory (ESO) 1998

Online publication: February 4, 1998