The ALMA-PILS survey: first detection of methyl isocyanide (CH3NC) in a solar-type protostar
Journal article, 2018

Methyl isocyanide (CH3NC) is the isocyanide with the largest number of atoms confirmed in the interstellar medium (ISM), but it is not an abundant molecule, having only been detected towards a handful of objects. Conversely, its isomer, methyl cyanide (CH3CN), is one of the most abundant complex organic molecules detected in the ISM, with detections in a variety of low- and high-mass sources. We use ALMA observations from the Protostellar Interferometric Line Survey (PILS) to search for methyl isocyanide and compare its abundance with that of its isomer methyl cyanide. We use a new line catalogue from the Cologne Database for Molecular Spectroscopy (CDMS) to identify methyl isocyanide lines. We also model the chemistry with an updated version of the three-phase chemical kinetics model MAGICKAL, presenting the first chemical modelling of methyl isocyanide to date. We detect methyl isocyanide for the first time in a solar-type protostar, IRAS 16293-2422 B, and present upper limits for its companion protostar, IRAS 16293-2422 A. Methyl isocyanide is found to be at least 20 times more abundant in source B compared to source A, with a CH3CN/CH3NC abundance ratio of 200 in IRAS 16293-2422 B and >5517 in IRAS 16293-2422 A. We also present the results of a chemical model of methyl isocyanide chemistry in both sources, and discuss the implications on methyl isocyanide formation mechanisms and the relative evolutionary stages of both sources.

ISM: molecules

Stars: formation

Stars: protostars

ISM: individual objects: IRAS 16293-2422



Hannah Calcutt

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

M. R. Fiechter

University of Groningen

University of Copenhagen

E. R. Willis

University of Virginia

H. S. P. Müller

University of Cologne

R. T. Garrod

University of Virginia

J. K. Jorgensen

University of Copenhagen

S. F. Wampfler

University of Bern

T. L. Bourke

Jodrell Bank Observatory

A. Coutens

University of Bordeaux

M. N. Drozdovskaya

University of Bern

N. F. W. Ligterink

Leiden University

L. E. Kristensen

University of Copenhagen

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 617 A95

Protostellar Interferometric Line Survey (PILS)

European Research Council (ERC), 2019-10-30 -- .

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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