Carbon chemistry in IRC+10216: Infrared detection of diacetylene

Abstract

We present the detection of C4H2 for first time in the envelope of the C-rich AGB star IRC+10216 based on high spectral resolution mid-IR observations carried out with the Texas Echelon-cross-Echelle Spectrograph (TEXES) mounted on the Infrared Telescope Facility (IRTF). The obtained spectrum contains 24 narrow absorption features above the detection limit identified as lines of the ro-vibrational C4H2 band nu6+nu8(sigma_u^+). The analysis of these lines through a ro-vibrational diagram indicates that the column density of C4H2 is 2.4(1.5)E+16 cm^(-2). Diacetylene is distributed in two excitation populations accounting for 20 and 80% of the total column density and with rotational temperatures of 47(7) and 420(120) K, respectively. This two-folded rotational temperature suggests that the absorbing gas is located beyond ~0.4"~20R* from the star with a noticeable cold contribution outwards from ~10"~500R*. This outer shell matches up with the place where cyanoacetylenes and carbon chains are known to form due to the action of the Galactic dissociating radiation field on the neutral gas coming from the inner layers of the envelope.

7 pages, 5 figures. Accepted for publication in the ApJ

References in corpus (13)

• The 2014 KIDA network for interstellar chemistry
• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• New molecules in IRC+10216: confirmation of C${}_5$S and tentative identification of MgCCH, NCCP, and SiH${}_3$CN
• Confirmation of circumstellar phosphine
• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds
• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
• The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales
• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
• The abundance of C2H4 in the circumstellar envelope of IRC+10216
• HST Images Reveal Dramatic Changes in the Core of IRC+10216
• Discovery of a Shell of Neutral Atomic Hydrogen Surrounding the Carbon Star IRC+10216
• Vibrationally Excited C${}_4$H

Cited by in corpus (4)

• Carbon-Chain Chemistry in the Interstellar Medium
• The chemistry of cosmic dust analogues from C, C${}_2$, and C${}_2$H${}_2$ in C-rich circumstellar envelopes
• Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through Interferometric Observations of HC${}_3$N
• Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn