Multiwavelength Spectroscopy of the Bipolar Outflow from Cepheus E

Abstract

Cepheus E is the site of an exceptional example of a protostellar outflow with a very young dynamical age and extremely high near-infrared luminosity. We combine molecular spectroscopic data from the submillimeter to the near-infrared in order to interpret the rotational excitation of CO and the rovibrational excitation of H₂. We conclude that C-type shocks with a paraboloidal bow shock geometry can simultaneously explain all the molecular excitations. Extinction accounts for the deviation of the column densities from local thermodynamic equilibrium. A difference in the extinction between the red- and blueshifted outflow lobes may account for the measured flux difference. The outflow is deeply embedded in a clump of density 10⁵ cm^-3, yet a good fraction of atomic hydrogen, about 40%, is required to explain the excitation and statistical equilibrium. We propose that this atomic component arises, self-consistently, from the dissociated gas at the apex of the leading bow shocks and the relatively long molecule reformation time. At least 20 bow shocks are required in each lobe, although these may be subdivided into smaller bows and turbulent shocked regions. The total outflow mechanical power and cooling amounts to over 30 L_solar, almost half the source's bolometric luminosity. Nevertheless, only about 6% of the clump mass has been set in outward motion by the outflow, allowing a collapse to continue.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.