A search for shock-excited optical emission from the outflows of massive young stellar objects

¹ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK e-mail: alvarez@mpia-hd.mpg.de
² Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Received: 10 August 2004
Accepted: 28 May 2005

Abstract

We have searched for optical shock-excited emission lines in the outer parts of the bipolar outflows from massive young stellar objects where the flow terminates and the extinction is expected to be low. The Taurus Tunable Filter (TTF) at the Anglo-Australian Telescope (AAT) was used to obtain narrow-band () images of the , [Nii] 6583, and [Sii] 6717/6731 lines around Mon R2 IRS3, S255 IRS1/3, GL 961 and GL 989. No clear examples of shocked emission were found. A bow shock feature in the GL 989 region maybe related with the molecular outflow NGC 2264 D. A weak optical bow-like feature is seen in GL 961, but which of the stars in the cluster is the driving source cannot be uniquely identified. Other emission line features were found in Mon R2 and S255 that are consistent with an Hii region origin. The observed fluxes and the upper limits were compared with predictions from radiative shock models available in the literature. Any head-on collisions of a jet with speeds of the order of 500 km s^-1 should have been detected if the extinction mag. Estimates of the extinction in the outer parts of the molecular clouds are somewhat lower than this, although it is possible that it could be higher local to any interaction regions due to swept up material. If the extinction is low, then the shocks must either be slower (<150 km s^-1) or very oblique (>), which would argue against the presence of highly collimated jets from high mass young stellar objects.