Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS)
Year: 2026
Type: article
Abstract: Context . Methyl cyanide (CH 3 CN) is one of the most abundant nitrogen-bearing complex organic molecules observed in the gas phase around both low- and high-mass protostars. However, very few observations exist with a broad enough frequency coverage and sufficiently high sensitivity to systematically characterize its minor isotopologues toward such regions. Aims . We add to this number by analyzing data toward BHR71-IRS1 taken with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) Large Program over a ∼33 GHz frequency range. Methods . We studied as many isotopologues of methyl cyanide as possible toward BHR71-IRS1. We found the column densities and excitation temperatures via spectral fitting and assuming local thermodynamic equilibrium. We then compared the derived column density ratios with those toward IRAS 16293-2422 A and B, V883 Ori, G31.41+0.31, and Sgr B2(N2b). Results . We detect CH 3 CN, CH 3 CN v 8 =1, 13 CH 3 CN, CH 3 13 CN, CH 3 C 15 N, CH 2 DCN, and CHD 2 CN. The column density ratio of 13 CH 3 CN/CH 3 13 CN is around unity, in agreement with previous observations. The CH 2 DCN/CH 3 CN ratios are similar for all the low-mass objects but are ∼1 order of magnitude higher than those toward Sgr B2(N2b). This could be due to a warmer pre-stellar phase or a different formation timescale of Sgr B2(N2b). Conclusions . The D/H ratios found from methyl cyanide isotopologues agree well with those of methanol toward BHR71-IRS1, likely pointing to the formation and deuteration of methyl cyanide in a similar star-formation phase as methanol (i.e., the pre-stellar phase). We find an increase in the methyl cyanide D/H ratios with the number of deuterium atoms, which suggests that the deuterated isotopologues may form later in the pre-stellar phase. Future COMPASS studies will increase the sample size of low-mass systems with methyl cyanide analysis and potentially examine some of the trends observed here statistically.
Source: Astronomy and Astrophysics
Institutions: European Southern Observatory, European Southern Observatory, Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, University of Copenhagen, Max Planck Institute for Radio Astronomy, National Radio Astronomy Observatory, Institut de Planétologie et d'Astrophysique de Grenoble, Université Grenoble Alpes, National Tsing Hua University, Tsinghua University, University of Bern, Physikalisch-Meteorologisches Observatorium Davos, Seoul National University, RIKEN Pioneering Research Institute, Purdue University West Lafayette, Eötvös Loránd University, Konkoly Observatory, Max Planck Institute for Astronomy, HUN-REN Research Centre for Astronomy and Earth Sciences, Massachusetts Institute of Technology, Max Planck Institute for Extraterrestrial Physics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, Gruber Foundation, National Radio Astronomy Observatory, European Commission, European Cooperation in Science and Technology, Centre National d’Etudes Spatiales, Korea Astronomy and Space Science Institute, National Research Foundation of Korea, Max-Planck-Gesellschaft, European Southern Observatory, Centre National de la Recherche Scientifique, National Astronomical Observatory of Japan, Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, Ministry of Science and ICT, South Korea, National Science and Technology Council, European Research Council, RIKEN, National Institutes of Natural Sciences, Nemzeti Kutatási, Fejlesztési és Innovaciós Alap
OpenAlex ID: W7220834962