The structure of the compact planetary nebulae CN 3-1 and M 3-27 and their extended haloes

We present long-slit optical spectroscopy and VLA-B radio continuum (lambda=3.6 cm) observations of the compact planetary nebulae Cn 3-1 and M 3- 27. The data allow us to distinguish different regions in both objects, to study their kinematical and emission properties, and to deduce different physical parameters in both nebulae. The radio and optical data show that the ionized shell of Cn 3-1 is an ellipsoid containing a bright, ring-like equatorial zone (size ~=2.6 arcsec, expansion velocity ~=14 km s^-1). Two bright, point-symmetric arcs have been detected in the core of Cn 3-1, extending from the equator towards the polar regions of the ellipsoid. The arcs seem to be filamentary structures located on the ellipsoid. The origin of the arcs could be related to some sort of collimated bipolar ejections along a rotating axis. Relatively high mean [N ii]/Hα~=0.83 and [S ii]/Hα~=0.056 line intensity ratios are found in Cn 3-1. Maximum values of [S ii]/Hα of ~=0.083 are found in the arcs. The estimated kinematical age and ionized mass of Cn 3-1 are ~=1300 yr and ~=4x10^-2 Msolar, respectively. M 3-27 is unresolved at 3.6 cm (size 〈=0.6 arcsec). The detected [N ii] and [S ii] emission lines arise in a compact (size 〈=1.4 arcsec), probably non-spherical region, which is identified with the ionized shell of M 3-27. The Hα emission from M 3-27 is dominated by strong stellar emission and exhibits a type III P Cygni profile with very extended wings (~=3000 km s^-1). A kinematical age of 〈=530 yr and an ionized mass of ~=3x10^-4 Msolar are estimated for M 3-27. Extended haloes (size ~=36 arcsec in Cn 3-1, ~=24 arcsec in M 3-27) have been spectroscopically detected in both objects through their [N ii] and/or Hα emissions. An analysis of the kinematical and emission properties of the haloes strongly suggests that they are reflection nebulosities and contain large amounts of neutral material, and that the distribution of neutral material in them is largely isotropic.