paper

Twenty years of observations of PM 1-188: Its chemical abundances and extraordinary kinematics

arXiv:2102.10022 · doi:10.1093/mnras/stab517

Abstract

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= 11.130.05, 12+log O/H = 8.040.04, 12+log N/H= 7.870.06, 12+log S/H = 7.180.10 and 12+log Ar = 5.330.16. 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 range, and both shells have expansion velocities of about 40 km s.

15 pages, 6 figures, acepted in MNRAS

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