Discovery of superthermal hydroxyl (OH) in the HH211 outflow

摘要

We present a 5-37 micron infrared spectrum obtained with the Spitzer SpaceTelescope toward the southeastern lobe of the young protostellar outflow HH211.The spectrum shows an extraordinary sequence of OH emission lines arising inhighly excited rotational levels up to an energy E/k~28200K above the groundlevel. This is, to our knowledge, by far the highest rotational excitation ofOH observed outside Earth. The spectrum also contains several pure rotationaltransitions of H2O (v=0), H2 (v=0) S(0) to S(7), HD (v=0) R(3) to R(6), andatomic fine-structure lines of [Fe II], [Si II], [Ne II], [S I], and [Cl I].The origin of the highly excited OH emission is most likely thephotodissociation of H2O by the UV radiation generated in the terminal outflowshock of HH211.