Physical properties of the fluorine and neutron-capture element-rich PN
  Jonckheere 900
  We performed detailed spectroscopic analyses of a young C-rich planetary
nebula (PN) Jonckheere900 (J900) in order to characterise the properties of the
central star and nebula. Of the derived 17 elemental abundances, we present the
first determination of eight elemental abundances. We present the first
detection of the [F IV] 4059.9 A, [F V] 13.4 um, and [Rb IV] 5759.6 A lines in
J900. J900 exhibits a large enhancement of F and neutron-capture elements Se,
Kr, Rb, and Xe. We investigated the physical conditions of the H2 zone using
the newly detected mid-IR H2 lines while also using the the previously measured
near-IR H2 lines, which indicate warm (~670 K) and hot (~3200 K) temperature
regions. We built the spectral energy distribution (SED) model to be consistent
with all the observed quantities. We found that about 67 % of all dust and gas
components (4.5x10^-4 Msun and 0.83 Msun, respectively) exists beyond the
ionisation front, indicating critical importance of photodissociation regions
in understanding stellar mass loss. The best-fitting SED model indicates that
the progenitor evolved from an initially ~2.0 Msun star which had been in the
course of the He-burning shell phase. Indeed, the derived elemental abundance
pattern is consistent with that predicted by a asymptotic giant branch star
nucleosynthesis model for a 2.0 Msun star with Z = 0.003 and partial mixing
zone mass of 6.0x10^-3 Msun. Our study demonstrates how accurately determined
abundances of C/F/Ne/neutron-capture elements and gas/dust masses help us
understand the origin and the internal evolution of the PN progenitors.
