Detection of Formaldehyde Towards the Extreme Carbon Star IRC+10216

Abstract

We report the detection of H2CO (formaldehyde) around the carbon-rich AGB star, IRC+10216. We find a fractional abundance with respect to molecular hydrogen of x(H2CO)= (1.3 {+1.5}{-0.8}) x 10^{-8}. This corresponds to a formaldehyde abundance with respect to water vapor of x(H2CO)/x(H2O)=(1.1 +/- 0.2) x 10^{-2}, in line with the formaldehyde abundances found in Solar System comets, and indicates that the putative extrasolar cometary system around IRC+10216 may have a similar chemical composition to Solar System comets. However, we also failed to detect CH3OH (methanol) around IRC+10216 and our upper limit of x(CH3OH)/x(H2O) < 7.7 x 10^{-4}, (3 sigma), indicates that methanol is substantially underabundant in IRC+10216, compared to Solar System comets. We also conclude, based on offset observations, that formaldehyde has an extended source in the envelope of IRC+10216 and may be produced by the photodissociation of a parent molecule, similar to the production mechanism for formaldehyde in Solar System comet comae. Preliminary mapping observations also indicate a possible asymmetry in the spatial distribution of formaldehyde around IRC+10216, but higher signal-to-noise observations are required to confirm this finding. This study is based on observations carried out with the IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). (abridged)

accepted to ApJ, 45 pages, 11 figures

References in corpus (4)

• Smoke Signals From IRC +10216: 1. Milliarcsecond Proper Motions of the Dust
• Water Vapor in Carbon-rich AGB Stars from the Vaporization of Icy Orbiting Bodies
• Detection of OH Towards the Extreme Carbon Star IRC+10216
• FUSE Observations of Possible Infalling Planetesimals in the 51 Ophiuchi Circumstellar Disk

Cited by in corpus (29)

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• Molecular shells in IRC+10216: tracing the mass loss history
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• Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind
• Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow
• Tunneling Rate Constants for H2CO+H on Amorphous Solid Water Surfaces
• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
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• Understanding the Chemical Complexity in Circumstellar Envelopes of C-rich AGB Stars: the Case of IRC +10216
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• Water vapor emission from IRC+10216 and other carbon-rich stars: model predictions and prospects for multitransition observations
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• Chemistry in AGB stars: successes and challenges
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• The distribution of H13CN in the circumstellar envelope around IRC+10216
• Hyperfine structure of the ${\mathbf{A}}^1\mathbf{\Pi }$ state of AlCl and its relevance to laser cooling and trapping
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• Measurement of the Electric Dipole Moment of AlCl by Stark Level Spectroscopy