Letter to the Editor

Heavy water around the L1448-mm protostar

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: codella@arcetri.astro.it
² Laboratoire d’Astrophysique de l’Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex, France
³ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy
⁴ Observatorio Astrónomico Nacional (IGN), Alfonso XII, 28014 Madrid, Spain
⁵ Laboratory of Molecular Astrophysics, CAB (CSIC-INTA), Crta Ajalvir km 4, 28840 Madrid, Spain
⁶ IRAM, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France

Received: 18 June 2010
Accepted: 13 October 2010

Abstract

Context. L1448-mm is the prototype of a low-mass Class 0 protostar driving a high-velocity jet. Given its bright H₂O spectra observed with ISO, L1448-mm is an ideal laboratory to observe heavy water (HDO) emission.

Aims. Our aim is to image the HDO emission in the protostar surroundings, the possible occurrence of HDO emission also investigating off L1448-mm, towards the molecular outflow.

Methods. We carried out observations of L1448-mm in the HDO(1₁₀–1₁₁) line at 80.6 GHz, an excellent tracer of HDO column density, with the IRAM Plateau de Bure Interferometer.

Results. We image for the first time HDO emission around L1448-mm. The HDO structure reveals a main clump at velocities close to the ambient one towards the the continuum peak that is caused by the dust heated by the protostar. In addition, the HDO map shows tentative weaker emission at ≃2000 AU from the protostar towards the south, which is possibly associated with the walls of the outflow cavity opened by the protostellar wind.

Conclusions. Using an LVG code, modelling the density and temperature profile of the hot-corino, and adopting a gas temperature of 100 K and a density of 1.5 × 10⁸ cm^-3, we derive a beam diluted HDO column density of ~7  ×  10¹³ cm^-2, corresponding to a HDO abundance of ~4 × 10^-7. In addition, the present map supports the scenario where HDO can be efficiently produced in shocked regions and not uniquely in hot corinos heated by the newly born star.