Deuterated methanol on a solar system scale around the HH212 protostar

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: ebianchi@arcetri.astro.it
² Università degli Studi di Firenze, Dipartimento di Fisica e Astronomia, via G. Sansone 1, 50019 Sesto Fiorentino, Italy
³ Univ. Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38401 Grenoble, France
⁴ CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38401 Grenoble, France
⁵ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, École Normale Supérieure, 75014 Paris, France
⁶ IGN, Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain
⁷ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁸ IRAM, 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
⁹ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, École Normale Supérieure, 75005 Paris, France
¹⁰ INAF–Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
¹¹ INAF–Istituto di Radioastronomia & Italian ALMA Regional Centre, via P. Gobetti 101, 40129 Bologna, Italy

Received: 19 June 2017
Accepted: 14 September 2017

Abstract

Context. Deuterium fractionation is a valuable tool for understanding the chemical evolution during the process that leads to the formation of a Sun-like planetary system.

Aims. Methanol is thought to be mainly formed during the prestellar phase, and its deuterated form keeps a memory of the conditions at that epoch. The unique combination of high angular resolution and sensitivity provided by ALMA enables us to measure methanol deuteration in the planet formation region around a Class 0 protostar and to understand its origin.

Methods. We mapped both the ¹³CH₃OH and CH₂DOH distribution in the inner regions (~100 au) of the HH212 system in Orion B. To this end, we used ALMA Cycle 1 and Cycle 4 observations in Band 7 with angular resolution down to ~0.̋15.

Results. We detected 6 lines of ¹³CH₃OH and 13 lines of CH₂DOH with upper level energies of up to 438 K in temperature units. We derived a rotational temperature of (171 ± 52) K and column densities of 7 × 10¹⁶ cm^-2 (¹³CH₃OH) and 1 × 10¹⁷ cm^-2 (CH₂DOH), respectively. This yields a D/H ratio of (2.4 ± 0.4) × 10^-2, which is lower by an order of magnitude than previously measured values using single-dish telescopes toward protostars located in Perseus. Our findings are consistent with the higher dust temperatures in Orion B with respect to the temperature derived for the Perseus cloud. The emission traces a rotating structure extending up to 45 au from the jet axis, which is elongated by 90 au along the jet axis. So far, the origin of the observed emission appears to be related with the accretion disc. Only higher spatial resolution measurements will be able to distinguish between different possible scenarios, however: disc wind, disc atmosphere, or accretion shocks.