A high-resolution line survey of IRC +10216 with Herschel/HIFI. First results: Detection of warm silicon dicarbide (SiC{_2})

José Cernicharo (1) , L. B. F. M. Waters (2) , Leen Decin (2) , Pierre J. Encrenaz (3, 4) , A. Tielens (5) , Marcelino Agúndez (1, 6) , E. de Beck (7) , Holger S. P. Müller (8) , Javier R. Goicoechea (1) , Michael J. Barlow (9) , A. Benz (10) , N. Crimier (1) , Fabien Daniel (1, 3, 4) , A. M. Di Giorgio (11) , Michael Fich (12) , T. C. Gaier (13) , P. Garcia-Lario (14) , Alex de Koter (2) , T. Khouri (2) , René Liseau (15) , R. Lombaert (7) , N. Erickson (16) , Juan R. Pardo (1) , John C. Pearson (13) , Russell Shipman (17) , C. Sánchez Contreras (1) , David Teyssier (14)

1 CAB - Centro de Astrobiología, Consejo Superior de Investigaciones Científicas (CSIC)/Instituto Nacional de Técnica Aeroespacial (INTA)
2 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
3 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
4 Instrumentation et télédétection
5 Leiden Observatory
6 LUTH (UMR_8102) - Laboratoire Univers et Théories
7 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven
8 Physikalisches Institut, Universität zu Köln
9 UCL - University College of London [London]
10 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
11 IFSI - Istituto di Fisica dello Spazio Interplanetario
12 University of Waterloo [Waterloo]
13 JPL - Jet Propulsion Laboratory
14 ESAC - European Space Astronomy Centre
15 Department of Radio and Space Science, Chalmers University of Technology
16 Department of Astronomy, University of Massachusetts
17 SRON - SRON Netherlands Institute for Space Research

We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901 GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5-636.5 GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal-to-noise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and, surprisingly, silicon dicarbide (SiC₂). We identified 55 SiC₂ transitions involving energy levels between 300 and 900 K. By analysing these rotational lines, we conclude that SiC₂ is produced in the inner dust formation zone, with an abundance of ~ 2 × 10^-7 relative to molecular hydrogen. These SiC₂ lines have been observed for the first time in space and have been used to derive an SiC₂ rotational temperature of ~204 K and a source-averaged column density of ~ 6.4 × 10¹⁵ cm^-2. Furthermore, the high quality of the HIFI data set was used to improve the spectroscopic rotational constants of SiC₂.

Domaines: Astrophysique [astro-ph]

José Cernicharo, L. B. F. M. Waters, Leen Decin, Pierre J. Encrenaz, A. Tielens, et al.. A high-resolution line survey of IRC +10216 with Herschel/HIFI. First results: Detection of warm silicon dicarbide (SiC{_2}). Astronomy and Astrophysics - A&A, 2010, 521, pp.L8. ⟨10.1051/0004-6361/201015150⟩. ⟨hal-03730799⟩