High SiO abundance in the HH212 protostellar jet

¹ LERMA, UMR 8112 du CNRS, Observatoire de Paris, École Normale Supérieure, Université Pierre et Marie Curie, Université de Cergy-Pontoise, 61 Av. de l’Observatoire, 75014 Paris, France
e-mail: sylvie.cabrit@obspm.fr
² INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³ Institut de Planétologie et d’Astrophysique de Grenoble, UMR 5274, UJF-Grenoble 1/CNRS-INSU, 38041 Grenoble, France
⁴ IRAM, 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France

Received: 8 June 2012
Accepted: 26 October 2012

Abstract

Context. Previous SiO maps of the innermost regions of HH212 set strong constraints on the structure and origin of this jet. They rule out a fast wide-angle wind, and tentatively favor a magneto-centrifugal disk wind launched out to 0.6 AU.

Aims. We aim to assess the SiO content at the base of the HH212 jet to set an independent constraint on the location of the jet launch zone with respect to the dust sublimation radius.

Methods. We present the first sub-arcsecond (0.″44 × 0.″96) CO map of the HH212 jet base, obtained with the IRAM Plateau de Bure Interferometer. Combining this with previous SiO(5–4) data, we infer the CO(2–1) opacity and mass-flux in the high-velocity jet and arrive at a much tighter lower limit to the SiO abundance than possible from the (optically thick) SiO emission alone.

Results. Gas-phase SiO at high velocity contains at least 10% of the elemental silicon if the jet is dusty, and at least 40% if the jet is dust-free, if CO and SiO have similar excitation temperatures. Such a high SiO content is challenging for current chemical models of both dust-free winds and dusty interstellar shocks.

Conclusions. Updated chemical models (equatorial dust-free winds, highly magnetized dusty shocks) and observations of higher J CO lines are required to elucidate the dust content and launch radius of the HH212 high-velocity jet.