IFU spectroscopy of Southern Planetary Nebulae V: Low-ionization
  structures
  In this 5th paper of the series, we examine the spectroscopy and morphology
of four southern Galactic planetary nebulae Hen 2-141, NGC5307, IC 2553, and
PB6 using new integral field spectroscopy data. The morphologies and ionization
structures of the sample are given as a set of emission-line maps. In addition,
the physical conditions, chemical compositions, and kinematical characteristics
of these objects are derived. The results show that PB6 and Hen 2-141 are of
very high excitation classes and IC 2553 and NGC5307 are mid to high excitation
objects. The elemental abundances reveal that PB6 is of Type I, Hen 2-141 and
IC 2553 are of Type IIa, and NGC5307 of Type IIb/III. The observations unveil
the presence of well- defined low-ionization structures or \knots" in all
objects. The diagnostic diagrams reveal that the excitation mechanism of these
knots is probably by photo-ionization of dense material by the nebular central
stars. The physical analysis of six of these knots show no significant
differences with their surrounding nebular gas, except their lower electron
densities. In spite of the enhancement of the low-ionization emission lines of
these knots, their chemical abundances are nearly comparable to their
surrounding nebulae, with the exception of perhaps slightly higher nitrogen
abundances in the NGC5307 knots. The integrated spectrum of IC 2553 reveals
that nearly all key lines that have led researchers to characterize its central
star as a weak-emission line star type are in fact of nebular origin.
