FAUST

V. Hot methanol in the [BHB2007] 11 protobinary system; hot corino versus shock origin

¹ IRAP, Université de Toulouse, CNRS, UPS, CNES, 31400 Toulouse, France
e-mail: cvastel@irap.omp.eu
² Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, 85748 Garching, Germany
³ Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38000 Grenoble, France
⁴ Centro de Astrobiologia (CSIC-INTA), Ctra. de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Spain
⁵ Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
⁶ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Florence, Italy
⁷ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
⁸ European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany
⁹ RIKEN Cluster for Pioneering Research, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan
¹⁰ Department of Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹¹ Research Center for the Early Universe, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹² Institut de Radioastronomie Millimétrique, 38406 Saint-Martin d’Hères, France
¹³ Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁴ Department of Chemistry, Biology, and Biotechnology, The University of Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
¹⁵ Astrochemistry Laboratory, Code 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
¹⁶ Cergy Paris Université, Sorbonne Université, Observatoire de Paris, PSL University, CNRS, LERMA, 95000, Cergy, France
¹⁷ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autόnoma de México, A.P. 3-72 (Xangari), 8701 Morelia, Mexico
¹⁸ Department of Astronomy, Xiamen University, Zengcuo’an West Road, Xiamen 361005, PR China
¹⁹ National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka-shi, Tokyo 181-8588, Japan
²⁰ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²¹ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada
²² Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
²³ Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
²⁴ Department of Chemistry, University of Virginia, McCormick Road, PO Box 400319, Charlottesville, VA, 22904, USA
²⁵ Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, TX 77005, USA
²⁶ Instituto de Astronomía, Universidad Nacional Autόnoma de México, Ciudad Universitaria, A.P. 70-264, Cuidad de México 04510, Mexico
²⁷ Institute of Low Temperature Science, Hokkaido University, N19W8, Kita-ku, Sapporo, Hokkaido 060-0819, Japan
²⁸ Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
²⁹ Steward Observatory, 933 N Cherry Ave., Tucson, AZ 85721, USA
³⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³¹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
³² Materials Science and Engineering, College of Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
³³ Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos, Universitat de Barcelona (IEEC-UB), Martí Franquès, 1, 08028 Barcelona, Catalunya, Spain
³⁴ Astronomical Institute, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan

Received: 24 February 2022
Accepted: 17 June 2022

Abstract

Aims. Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the build-up of chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance.

Methods. We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disc has previously been detected.

Results. Twelve methanol lines have been detected with upper energies in the [45–537] K range along with one ¹³CH₃OH transition and one methyl formate (CH₃OCHO) line blended with one of the methanol transitions. The methanol emission is compact (FWHM ~ 0.5″) and encompasses both protostars, which are separated by only 0.2″ (28 au). In addition, the overall methanol line emission presents three velocity components, which are not spatially resolved by our observations. Nonetheless, a detailed analysis of the spatial origin of these three components suggests that they are associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A radiative transfer analysis of the methanol lines gives a kinetic temperature of [100–140] K, an H₂ volume density of 10⁶–10⁷ cm⁻³ and column density of a few 10¹⁸ cm⁻² in all three components with a source size of ~0.15″. Thus, this hot and dense gas is highly enriched in methanol with an abundance as high as 10⁻⁵. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects.

Conclusions. Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis.