THE PECULIAR DISTRIBUTION OF CH{sub 3}CN IN IRC +10216 SEEN BY ALMA

Journal Article · Tue Dec 01 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/814/2/143· OSTI ID:22521840

Agúndez, M.; Cernicharo, J.; Quintana-Lacaci, G.; Prieto, L. Velilla ^[1]; Castro-Carrizo, A.; Guélin, M. ^[2]; Marcelino, N. ^[3]

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1. Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco (Spain)
2. Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 St. Martin d’Héres (France)
3. INAF, Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy)

IRC +10216 is a circumstellar envelope around a carbon-rich evolved star which contains a large variety of molecules. According to interferometric observations, molecules are distributed either concentrated around the central star or as a hollow shell with a radius of ∼15″. We present ALMA Cycle 0 band 6 observations of the J = 14 – 13 rotational transition of CH{sub 3}CN in IRC +10216, obtained with an angular resolution of 0.″76 × 0.″61. The bulk of the emission is distributed as a hollow shell located at just ∼2″ from the star, with a void of emission in the central region up to a radius of ∼1″. This spatial distribution is markedly different from those found to date in this source for other molecules. Our analysis indicates that methyl cyanide is not formed in either the stellar photosphere or far in the outer envelope, but at radial distances as short as 1″–2″, reaching a maximum abundance of ∼0.02 molecules cm{sup −3} at 2″ from the star. Standard chemical models of IRC +10216 predict that the bulk of CH{sub 3}CN molecules should be present at a radius of ∼15″ where other species such as polyyne radicals and cyanopolyynes are observed, with an additional inner component within 1″ from the star. The non-uniform structure of the circumstellar envelope and grain surface processes are discussed as possible causes of the peculiar distribution of methyl cyanide in IRC +10216.

• OSTI ID: 22521840
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 814; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACETONITRILE
CARBON
CARBON STARS
CYANIDES
ELEMENT ABUNDANCE
MOLECULES
PHOTOSPHERE
RADICALS
RESOLUTION
SPATIAL DISTRIBUTION
STAR EVOLUTION