Twenty years of observations of PM 1-188: Its chemical abundances and
  extraordinary kinematics
  The analysis of 20 years of spectrophotometric data of the double shell
planetary nebula PM\,1-188 is presented, aiming to determine the time evolution
of the emission lines and the physical conditions of the nebula, as a
consequence of the systematic fading of its [WC\,10] central star whose
brightness has declined by about 10 mag in the past 40 years. Our main results
include that the [\ion{O}{iii}], [\ion{O}{ii}], [\ion{N}{ii}] line intensities
are increasing with time in the inner nebula as a consequence of an increase in
electron temperature from 11,000 K in 2005 to more than 14,000 K in 2018, due
to shocks. The intensity of the same lines are decreasing in the outer nebula,
due to a decrease in temperature, from 13,000 K to 7,000 K, in the same period.
The chemical composition of the inner and outer shells was derived and they are
similar. Both nebulae present subsolar O, S and Ar abundances, while they are
He, N and Ne rich. For the outer nebula the values are 12+log He/H=
11.13$\pm$0.05, 12+log O/H = 8.04$\pm$0.04, 12+log N/H= 7.87$\pm$0.06, 12+log
S/H = 7.18$\pm$0.10 and 12+log Ar = 5.33$\pm$0.16. The O, S and Ar abundances
are several times lower than the average values found in disc non-Type I PNe,
and are reminiscent of some halo PNe. From high resolution spectra, an outflow
in the N-S direction was found in the inner zone. Position-velocity diagrams
show that the outflow expands at velocities in the $-$150 to 100 km s$^{-1}$
range, and both shells have expansion velocities of about 40 km s$^{-1}$.
