Detailed Studies of IPHAS sources. II. Sab 19, a true planetary nebula and its mimic crossing the Perseus Arm

TL;DR

This paper provides a detailed multi-wavelength analysis of the planetary nebula Sab 19, revealing its structure, chemical composition, and kinematic properties, and clarifying its nature and relation to the surrounding interstellar medium.

Contribution

It offers the first comprehensive study of Sab 19 using radio, infrared, and optical data, identifying it as a type III planetary nebula and clarifying the nature of its external shell.

Findings

Sab 19 is a type III planetary nebula with a double-shell structure.

The external shell is likely a Strömgren zone in the interstellar medium, not physically associated with the nebula.

The progenitor star crossed the Perseus Arm during its evolution.

Abstract

The INT Photometric H$\alpha$ Survey (IPHAS) has provided us with a number of new-emission line sources, among which planetary nebulae (PNe) constitute an important fraction. Here we present a detailed analysis of the IPHAS nebula Sab\,19 (IPHASX\,J055242.8+262116) based on radio, infrared, and optical images and intermediate- and high-dispersion longslit spectra. Sab\,19 consists of a roundish 0.10 pc in radius double-shell nebula surrounded by a much larger 2.8 pc in radius external shell with a prominent H-shaped filament. We confirm the nature of the main nebula as a PN whose sub-solar N/O ratio abundances, low ionized mass, peculiar radial velocity, and low-mass central star allow us to catalog it as a type III PN. Apparently, the progenitor star of Sab\,19 became a PN when crossing the Perseus Arm during a brief visit of a few Myr. The higher N/O ratio and velocity shift $\simeq$40 \kms\ of the external shell with respect to the main nebula and its large ionized mass suggest that it is not truly associated with Sab\,19, but it is rather dominated by a Str\"omgren zone in the interstellar medium ionized by the PN central star.