The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO₂ emission

¹ INAF − Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: lpodio@arcetri.astro.it
² IRAM, 300 rue de la Piscine, 38406 Saint-Martin d’Hères, France
³ LERMA, Observatoire de Paris, UPMC Univ. Paris 06, PSL Research University, Sorbonne Universités, CNRS, 75014 Paris, France
⁴ UJF-Grenoble1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble 38041, France
⁵ IGN, Observatorio Astronómico Nacional, Alfonso XIII 3, 28014 Madrid, Spain
⁶ Academia Sinica Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 106, Taiwan
⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁸ INAF, Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy

Received: 1 February 2015
Accepted: 15 May 2015

Abstract

Context. The investigation of the disk formation and jet launching mechanism in protostars is crucial to understanding the earliest stages of star and planet formation.

Aims. We aim to constrain the physical and dynamical properties of the molecular jet and disk of the HH 212 protostellar system at unprecedented angular scales, exploiting the capabilities of the Atacama Large Millimeter Array (ALMA).

Methods. The ALMA observations of HH 212 in emission lines from sulfur-bearing molecules, SO 9₈−8₇, SO 10₁₁−10₁₀, SO₂8_2,6−7_1,7, are compared with simultaneous CO 3−2, SiO 8−7 data. The molecules column density and abundance are estimated using simple radiative transfer models.

Results. SO 9₈−8₇ and SO₂8_2,6−7_1,7 show broad velocity profiles. At systemic velocity, they probe the circumstellar gas and the cavity walls. Going from low to high blue- and red-shifted velocities the emission traces the wide-angle outflow and the fast (~100−200 km s^-1), collimated (~90 AU) molecular jet revealing the inner knots with timescales ≤50 yr. The jet transports a mass-loss rate ≥ 0.2−2 × 10^-6 M_⊙ yr^-1, implying high ejection efficiency (≥ 0.03−0.3). The SO and SO₂ abundances in the jet are ~ 10^-7−10^-6. SO 10₁₁−10₁₀ emission is compact and shows small-scale velocity gradients, indicating that it originates partly from the rotating disk previously seen in HCO⁺ and C¹⁷O, and partly from the base of the jet. The disk mass is ≥ 0.002−0.013 M_⊙ and the SO abundance in the disk is ~ 10^-8−10^-7.

Conclusions. SO and SO₂ are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1−40% of sulfur is in SO and SO₂ due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3−4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly gravitationally unstable.