A λ 3 mm Line Survey toward the Circumstellar Envelope of the Carbon-rich AGB Star IRC+10216 (CW Leo)

Abstract

We present an unbiased λ 3 mm spectral line survey (between 84.5 and 115.8 GHz), conducted by the Purple Mountain Observatory 13.7 m radio telescope, together with updated modeling results, toward the carbon-rich asymptotic giant branch star IRC+10216 (CW Leo). A total of 75 spectral lines (96 transitions) are detected, and identified to arise from 19 molecules: C _2 H, l -C _3 H, C _4 H, CN, C _3 N, HC _3 N, HC _5 N, HCN, HNC, CH _3 CN, MgNC, CO, c -C _3 H _2 , SiC _2 , SiO, SiS, CS, C _2 S, C _3 S, and their isotopologues. Among them, one molecular emission line (H ^13 CCCN J = 13–12) is discovered in IRC+10216 for the first time. The excitation temperature, column density, and fractional abundance of the detected species are deduced by assuming they are in local thermodynamic equilibrium. In addition, the isotopic ratios of [ ^12 C]/[ ^13 C], [ ^32 S]/[ ^34 S], [ ^28 Si]/[ ^29 Si], and [ ^12 C ^34 S]/[ ^13 C ^32 S] are obtained and found to be consistent with previous studies. Finally, we summarize all of the 106 species detected in IRC+10216 to date with their observed and modeled column densities for the convenience of future studies.

Keywords

• Astrochemistry