Volume 426, Number 2, November I 2004
|Page(s)||L49 - L52|
|Published online||11 October 2004|
Letter to the Editor
Detection of the SiNC radical in IRC+10216
IRAM, 300 rue de la piscine, 38406 Saint-Martin-d'Hères, France e-mail: firstname.lastname@example.org
2 Institute of Astronomy and Astrophysics, Academia Sinica, 128 Section 2, PO Box 1-87, Nankang, Taipei 115, Taiwan
3 Instituto de Estructura de la Materia, C/Serrano 121, 28006 Madrid, Spain
4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Accepted: 6 September 2004
Following discovery of the free radical SiCN in the C-star envelope IRC+10216, we report the detection in the same source of its isomer SiNC. The microwave spectra of SiNC and SiCN were studied in the laboratory and their rotational transition frequencies are accurately known. The ground fine structure state of SiNC, , gives rise to a series of rotational transitions, spaced by 12.8 GHz, each with Λ-doubling. Five weak lines are detected with the IRAM 30-m telescope at the frequencies of the (e), (f), (f) and (e) and (f) rotational transitions. Other SiNC lines from these or adjacent rotational transitions are found to be blended with stronger lines from known molecules. The lines assigned to SiNC have a cusped shape, characteristic of species confined to a hollow shell in the outer circumstellar envelope. They are twice weaker than their SiCN counterparts, which have the same shape, and presumably arise in the same region of the envelope. SiNC and SiCN have about the same abundance in IRC+10216, ~4 10-9 with respect to H2. This contrasts with HCN, HC3N and HC5N, for which the cyanide to isocyanide abundance ratio is >100.
Key words: stars: circumstellar matter / stars: AGB and post-AGB / stars: individual: IRC+10216 / ISM: molecules / radio lines: stars
© ESO, 2004
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