Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157

Edgar Mendoza (1) , B. Lefloch (1) , A. López-Sepulcre (1) , C. Ceccarelli (1) , C. Codella , H. M. Boechat-Roberty , R. Bachiller

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

Interstellar molecules with a peptide link (-NH-C(=O)-), like formamide (NH₂CHO), acetamide (NH₂COCH₃) and isocyanic acid (HNCO), are particularly interesting for their potential role in pre-biotic chemistry. We have studied their emission in the protostellar shock regions L1157-B1 and L1157-B2, with the IRAM 30 m telescope, as part of the ASAI Large Programme. Analysis of the line profiles shows that the emission arises from the outflow cavities associated with B1 and B2. Molecular abundances of ≈(0.4-1.1) × 10^-8 and (3.3-8.8) × 10^-8 are derived for formamide and isocyanic acid, respectively, from a simple rotational diagram analysis. Conversely, NH₂COCH₃ was not detected down to a relative abundance of a few ≤10^-10. B1 and B2 appear to be among the richest Galactic sources of HNCO and NH₂CHO molecules. A tight linear correlation between their abundances is observed, suggesting that the two species are chemically related. Comparison with astrochemical models favours molecule formation on icy grain mantles, with NH₂CHO generated from hydrogenation of HNCO.

Mots clés: astrobiology; astrochemistry; methods: observational; ISM: abundances; ISM: jets and outflows; ISM: molecules

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

Edgar Mendoza, B. Lefloch, A. López-Sepulcre, C. Ceccarelli, C. Codella, et al.. Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157. Monthly Notices of the Royal Astronomical Society, 2014, 445, pp.151-161. ⟨10.1093/mnras/stu1718⟩. ⟨insu-03618156⟩