Optical Polarimetry of HH 135/HH 136

We present optical linear polarimetry in the line of sight to HH135/HH136.The polarimetry of the field stars reveals two populations: one corresponds toa foreground interstellar component; the other originates in the interstellarmedium in the vicinity of the Herbig-Haro pair and, therefore, can be used tostudy the magnetic field in the star forming region. Its direction is alignedwith the jet of HH135/HH136, which could be an indication that the interstellarmagnetic field is important in the outflow collimation. The interstellarmagnetic field magnitude was estimated to be of order 90 uG. According torecent numerical simulations, an interstellar magnetic field of such strengthcan be important in the definition of the outflow direction. There is alsoevidence that the associated dark cloud has an elongation parallel to themagnetic field. Our image polarimetry of the extended emission associated withHH135/HH136 shows a centro-symmetric pattern pointing to the knot E of HH136.Previous near infrared polarimetry traces a different illumination center,namely IRAS 11101-5829 - the probable exciting source of the system. Thisdiscrepancy can be explained if the YSO emission is completely blocked inoptical wavelengths and the dominant optical source in the region is the knotE, whose nature is uncertain. A discussion of the spectral energy distributionsof HH136-E and IRAS 11101-5829 is presented.Comment: Accepted for publication in The Astronomical Journal, 27 pages, 10 figure