2014MNRAS.442..995M

IRAS 18197-1118 is a stellar-like object that has been classified as a planetary nebula from its radio continuum emission and high [S iii]λ9532 to Paschen 9 line intensity ratio, as derived from direct images. We present intermediate- and high-resolution, optical spectroscopy, Very Large Array 8.46 GHz radio continuum data, and narrow-band optical images of IRAS 18197-1118 aimed at confirming its planetary nebula nature, and analysing its properties. The optical spectrum shows that IRAS 18197-1118 is a medium-excitation planetary nebula suffering a high extinction (cHβ ≃ 3.37). The optical images do not resolve the object but the 8.46 GHz image reveals an elliptical shell of ≃ 2.7x1.6 arcsec2 in size, a compact central nebular region, and possible bipolar jet-like features, indicating several ejection events. The existence of a compact central nebula makes IRAS 18197-1118 singular because this kind of structure is observed in a few PNe only. An expansion velocity ≃ 20 km/s and a systemic velocity (LSR) ≃ +95 km/s are obtained for the object. An electron density of ≃ 3.4x10⁴/cm3 and an ionized mass of ≃ 2.1x10^–2 M_☉ are deduced from the 8.46 GHz radio continuum data for an estimated statistical distance of 6 kpc. Helium abundance is high but nitrogen is not enriched, which is not consistently reproduced by evolutionary models, suggesting different abundances in the elliptical shell and central region. The properties of IRAS 18197-1118 indicate a relatively young planetary nebula, favour a distance of ≳ 6 kpc, and strongly suggest that it is an inner-disc planetary nebula.