Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) -- IV. Methyl cyanide isotopologues toward BHR71-IRS1

@misc{nazari2026complex,
  title = {{Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) -- IV. Methyl cyanide isotopologues toward BHR71-IRS1}},
  author = {P. Nazari and A. Coutens and J. K. Jørgensen and A. Belloche and A. L. Plunkett and S. Maret and D. Harsono and M. N. Drozdovskaya and J. -E. Lee and F. Cruz-Sáenz de Miera and J. Ferrer Asensio and M. L. R. van 't Hoff and J. -H. Jeong and Á Kóspál and B. A. McGuire and S. Spezzano and Y. -L. Yang and H. -S. Yun and S. Zeng},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.08754},
  eprint = {2610.08754},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.08754},
}

TY  - UNPB
TI  - Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) -- IV. Methyl cyanide isotopologues toward BHR71-IRS1
AU  - P. Nazari
AU  - A. Coutens
AU  - J. K. Jørgensen
AU  - A. Belloche
AU  - A. L. Plunkett
AU  - S. Maret
AU  - D. Harsono
AU  - M. N. Drozdovskaya
AU  - J. -E. Lee
AU  - F. Cruz-Sáenz de Miera
AU  - J. Ferrer Asensio
AU  - M. L. R. van 't Hoff
AU  - J. -H. Jeong
AU  - Á Kóspál
AU  - B. A. McGuire
AU  - S. Spezzano
AU  - Y. -L. Yang
AU  - H. -S. Yun
AU  - S. Zeng
PY  - 2026
DA  - 2026/10/06
PB  - arXiv
DO  - 10.48550/arxiv.2610.08754
UR  - https://arxiv.org/abs/2610.08754
AB  - Methyl cyanide is one of the most abundant nitrogen-bearing complex organic molecules observed in the gas phase around 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. We add to this number by analyzing data toward BHR71-IRS1 taken as part of the Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) Large Program over a ~33 GHz frequency range. 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). We detect CH3CN, CH3CN v_8=1, 13-CH3CN, CH3-13-CN, CH3C-15-N, CH2DCN, and CHD2CN. The column density ratio of 13-CH3CN/CH3-13-CN is around unity, in agreement with previous observations. The CH2DCN/CH3CN 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). 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.
ER  -