2018A&A...620A..84B

Context. Many round or roundish planetary nebulae (PNe) show multiple shells and halo structures during their evolutionary stage near the maximum temperature of their central star. Controversial debate is ongoing if these structures are recombination halos, as suggested by hydrodynamic modeling efforts, or ionized material. Recently, we discovered a halo with somewhat unusual structures around the sparsely studied PN IC 5148 and present for the first time spectroscopy going out to the halo of such a PN.
Aims. We investigate the spatial distribution of material and its ionization state from the center of the nebula up to the very outskirts of the halo.
Methods. We obtained long-slit low resolution spectroscopy (FORS2 at VLT) of the nebula in two position angles, which we used to investigate the nebular structure and its halo in the optical range from 450 to 880 nm. In addition we used medium resolution spectra taken with X-shooter at VLT ranging from 320 nm to 2.4 µm to derive atmospheric parameters for the central star. We obtained the distance and position in the Galaxy from various methods combined with Gaia DR2 data. We also applied Cloudy models to the nebula in order to derive physical parameters of the various regions.
Results. We obtained spatially resolved structures and detailed descriptions of the outrunning shock front and a set of unusual halo structures denoted to further shock. The halo structures appears clearly as hot ionized material. Furthermore, we derived a reliable photometric value for the central star at a Gaia distance of D=1.3kpc. Considering the large distance z=1.0kpc from the galactic plane together to its non-circular motion in the galaxy and, a metallicity only slightly below that of typical disk PNe, most likely IC 5148 originates from a thick disk population star.