IRAS18197-1118 is a stellar-like object that has been classified as a
planetary nebula from its radio continuum emission and high [SIII]9532 to
Paschen9 line intensity ratio, as derived from direct images. We present
intermediate- and high-resolution, optical spectroscopy, VLA 8.46 GHz radio
continuum data, and narrow-band optical images of IRAS18197-1118 aimed at
confirming its planetary nebula nature, and analyzing its properties. The
optical spectrum shows that IRAS18197-1118 is a medium-excitation planetary
nebula suffering a high extinction (c(H_beta) ~3.37). The optical images do not
resolve the object but the 8.46 GHz image reveals an elliptical shell of
~2.7x1.6 arcsec^2 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 IRAS18197-1118 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 ~3.4x10^4 cm-3 and an ionized mass of ~2.1x10^-2 M_sun 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 IRAS18197-1118
indicate a relatively young planetary nebula, favor a distance of >~6 kpc, and
strongly suggest that it is an inner-disc planetary nebula.Comment: Accepted by MNRAS. 8 pages, 5 figures, 4 table
