Letter to the Editor

Observations of high-J SiO emission along the HH211 outflow

¹ INAF-Osservatorio Astronomico di Roma, 00040 Monteporzio Catone, Italy
² Istituto di Radioastronomia, CNR, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy
³ Department of Physics, University of Cambridge, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK

Corresponding author: B. Nisini, bruni@coma.mporzio.astro.it

Received: 11 September 2002
Accepted: 8 October 2002

Abstract

Spectra of the pure rotational SiO –10 and –7 lines, at 477.5 GHz and 347.3 GHz respectively, have been obtained along the HH211 protostellar jet. Bright emission has been observed localized inside about 15″ of projected distance from the central source, where a compact and collimated SiO jet was previously discovered by means of SiO –0 interferometric observations (Chandler & Richer [CITE]). The detection of the high-J lines testifies for the extreme conditions of density and temperature of the SiO emission. Values of  K and  cm^-3 are inferred from the observed line ratios, while a SiO abundance in the range ~ has been estimated through a comparison with the CO rotational lines at observed by the ISO Long Wavelength Spectrometer. Both the estimated physical conditions and abundance are in agreement with a picture in which the observed SiO emission directly arises at the front of a C-type shock with  km s^-1, where all the silicon released from the grains by sputtering and/or grain-grain collisions is converted into gas-phase SiO.