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Astron. Astrophys. 317, 907-910 (1997)

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Detection of CH 3.3 GHz emission from the intermediate-velocity cloud G90+39(Draco)

Ronald Stark 1, Peter Kalberla 2 and Rolf Güsten 1

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Received 3 May 1995 / Accepted 17 June 1995


We report the detection of the CH [FORMULA], [FORMULA] ground-state hyperfine transitions at 3.3 GHz in the inter-mediate-velocity cloud G90+39(Draco). The lines were measured with the Effelsberg 100m radio telescope and their main-line strength varies between [FORMULA] K. The emission is found to be optically thin and the derived CH column density ranges between [FORMULA] cm-2. The CH column density as well as the derived dust-to-gas ratio indicate that the Draco cloud resembles the translucent high-latitude clouds at local velocities. The measurements are used to calculate the molecular hydrogen column density using the theoretically determined linear relation between N (CH) and N (H2). We find N (H [FORMULA] cm-2. These values are about a factor five higher than the ones found via the empirical CO/H2 conversion ratio of Herbstmeier et al. (1993).

Key words: ISM: abundances – molecules – ISM: Draco cloud= G 90+39 – radio lines: ISM

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998