The collimated outflows of the planetary nebula Hu 1-2: proper motion and radial velocity measurements

Hu 1-2 is a planetary nebula that contains an isolated knot located north-west of the main nebula, which could be related to a collimated outflow. We present a subarcsecond Hα+[N ii] image and a high-resolution, long-slit spectrum of Hu 1-2 that allow us to identify the south-eastern counterpart of the north-western knot and to establish their high-velocity (>340 km s−1), collimated bipolar outflow nature. The detection of the north-western knot in Palomar Observatory Sky Atlas (POSS) red plates allows us to carry out a proper motion analysis by combining three POSS red plates and two narrow-band Hα+[N ii] CCD images, with a time baseline of ≃57 yr. A proper motion of 20 ± 6 mas yr−1 along position angle 312°± 15° and a dynamical age of 1375 yr are obtained for the bipolar outflow. The measured proper motion and the spatio-kinematical properties of the bipolar outflow yield a lower limit of 2.7 kpc for the distance to Hu 1-2.