Astron. Astrophys. Suppl. Ser. 142, 181-215

A $\lambda$2 mm molecular line survey of the C-star envelope IRC+10216

J. Cernicharo¹ - M. Guélin² - C. Kahane³

Send offprint request: J. Cernicharo

1 - CSIC, Instituto de Estructura de la Materia, C/Serrano 121, 28006 Madrid, Spain
e-mail: cerni@astro.iem.csic.es
2 - IRAM, Domaine Universitaire de Grenoble, 300 rue de la Piscine, 38406 St Martin d'Hères, France
e-mail: guelin@iram.fr
3 - Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP. 53, 38041 Grenoble Cedex, France

Received April 23; accepted August 6, 1999

Abstract:

The mm-wave spectrum of the C-star envelope IRC+10216 has been continuously surveyed between 129.0 and 172.5 GHz with the IRAM 30-m telescope. 380 lines are detected, of which 317 have been identified. The identified lines arise from 30 different molecules and radicals which, in their vast majority, are not observed in hot and dense interstellar clouds such as Orion A or W3(OH). Actually, half of the molecular species identified in the mm-wave spectrum of IRC+10216 were first observed in the course of this spectral survey.

The new species include several carbon-chain molecules and radicals, as well as silicon and metallic compounds. They also include molecules containing rare isotopes of C, Mg, Si, S and Cl, whose elemental abundance ratios in the envelope are redetermined. We observe, in particular, four ¹³C isotopomers of C₄H, three of C₃N and HC₃N, and four doubly-substituted isotopomers of SiS and CS.

63 lines remain unidentified. Probably, a large fraction of those are rotational transitions inside the excited bending states of the abundant species NaCN, C₅H, and C₆H. We can also expect some lines to be ground state transitions of poorly known silicon and metal compounds, such as the slightly asymmetrical top molecule SiCSi.

Key words: line identification -- surveys -- stars: AGB and post-AGB -- stars: carbon -- stars: circumstellar matter -- stars: individual: IRC+10216 -- ISM: molecules -- radio lines: stars