Abstract
Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the most luminous outflows detected so far. Using the IRAM 30m telescope, we searched for and detected the para-water line emission at 183 GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2" resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the water emission arises from warm ($\sim 200\K$), dense ($(1-2)\times 10^6\cmmt$) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel.
Highlights
Water is a key molecule for oxygen chemistry in the interstellar gas, and in the dynamical evolution of star-forming regions, because it is one of the main gas coolants (Kaufman & Neufeld 1996; Bergin et al 1998)
The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope
In this Letter, we report on observations of the p-H2O 313−220 line in the star-forming core Cep E with the IRAM 30 m telescope1
Summary
Water is a key molecule for oxygen chemistry in the interstellar gas, and in the dynamical evolution of star-forming regions, because it is one of the main gas coolants (Kaufman & Neufeld 1996; Bergin et al 1998). Detected large-scale p-H2O 313−220 line emission in giant molecular clouds and star-forming regions and they showed that this line can be used to investigate the spatial distribution of H2O in protostellar environments at an angular resolution comparable to the size of the protostellar cores (14 at the IRAM 30 m telescope). Observing the low-mass protostellar outflows HH 7-11 and L1448, Cernicharo et al (1996) detected water line emission arising from shocks associated with the Herbig-Haro objects in the outflows. Observations of the millimeter lines of SiO observations reveal the presence of strong shocks along the outflow (L96). Because it is usually undetected in the cold, quiescent molecular gas, SiO is a good tracer of shocks that are strong enough to release refractory elements from grain cores.
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