Observational evidence of the formation of cyanopolyynes in CRL618 through the polimerization of HCN

Abstract

The abundance ratio of consecutive members of the cyanopolyynes family has been explored in CRL618 using data acquired in a complete line survey covering the frequency range 81-356 GHz. The Jup range explored for the different molecules is the following: 1 to 4 for HCN and HNC, 9 to 39 for HC3N, 31 to 133 for HC5N, and 72 to 85 for HC7N (not detected beyond Jup=85). The lowest vibrationally excited state of HC7N (nu_15 at 62 cm^-1) has been tentatively detected. Data analysis has been performed by extending our previous geometrical and radiative transfer model of the slowly expanding envelope (SEE) surrounding the compact central continuum source of CRL 618, that was established from the study of rotational lines in several vibrationally excited states of HC_3N. The new lines analyzed here require to model the high velocity wind (HVW) component and the colder circumstellar gas, remnant of the AGB phase of CRL618. The derived HC3N/HC5N and HC5N/HC7N abundance ratios from this set of uniformly calibrated lines are between 3 and 6 in the different regions, similar to standard values in the CSM and ISM, and consistent with previous estimates obtained from ISO observations and chemical models. However, the abundance ratios of HC3N, HC5N and HC7N with respect to HCN are at least two orders of magnitude larger than those typical for AGB C-rich stars, such as IRC+10216. This fact indicates that, in the short transition toward the Planetary Nebula phase, HCN is quickly reprocessed into longer cyanopolyyne chains. A similar behavior was previously found in this object for the polyacetylenic chains (C(2n)H2).

arXiv comment8 figures, accepted in ApJ main journal

References in corpus (2)

• Chemical Evolution of the Circumstellar Envelopes of Carbon-rich Post-AGB objects
• The slowly expanding envelope of CRL618 probed with HC3N rotational ladders

Cited by in corpus (13)

• Probing non polar interstellar molecules through their protonated form: Detection of protonated cyanogen (NCCNH+)
• The growth of carbon chains in IRC+10216 mapped with ALMA
• Molecular survey of CRL618
• A spectral line survey of NGC 7027 at millimeter wavelengths
• Carbon-Chain Chemistry in the Interstellar Medium
• Herschel-SPIRE FTS spectroscopy of the carbon-rich objects AFGL 2688, AFGL 618 and NGC 7027
• A molecular line survey of the extreme carbon star CRL 3068 at millimeter wavelengths
• Carbon Chain Molecules Toward Embedded Low-Mass Protostars
• The abundances of polyacetylenes towards CRL618
• Rapid Angular Expansion of the Ionized Core of CRL 618
• Mapping the Central Region of the PPN CRL 618 at Sub-arcsecond Resolution at 350 GHz
• X-ray photodesorption and proton destruction in protoplanetary disks: pyrimidine
• The spectra of evolved stars at 20--25\,GHz: tracing circumstellar chemistry during the asymptotic giant branch to planetary nebula transition