Criss-cross mapping BD+30 3639: a new kinematic analysis technique
  We present a new analysis of kinematic data of the young planetary nebula
BD+30 3639. The data include spectroscopic long-slit and internal proper motion
measurements. In this paper we also introduce a new type of mapping of
kinematic proper motion data that we name "criss-cross" mapping. It basically
consists of finding all points where extended proper motion vectors cross
converge. From the crossing points a map is generated which helps to interpret
the kinematic data. From the criss-cross mapping of BD+30 3639, we conclude
that the kinematic center is approximately 0.5 arcsec offset to the South-East
from the central star. The mapping does also show evidence for a non-homologous
expansion of the nebula that is consistent with a disturbance aligned with the
bipolar molecular bullets.
