The Ionization State of the Halo Planetary Nebula NGC 2438

TL;DR

This study investigates the ionization state of the halo in planetary nebula NGC 2438 using imaging and spectroscopy, concluding that the halo is fully ionized based on temperature and density measurements.

Contribution

It provides detailed morphological and physical analysis of the halo, clarifying its ionization state through new observational data and temperature diagnostics.

Findings

Halo is fully ionized based on temperature data

Electron density varies, indicating changing filling factors

Supports the view that halos are not mainly recombined gas

Abstract

NGC 2438 is a classical multiple shell or halo planetary nebula (PN). Its central star and the main nebula are well studied. Also it was target of various hydrodynamic simulations (Corradi et al. 2000). This initiated a discussion whether the haloes are mainly containing recombined gas (Schoenberner et al. 2002), or if they are still ionized (Armsdorfer et al. 2003). An analysis of narrow-band images and long slit spectra at multiple slit positions was done to obtain a deeper look on morphological details and the properties of the outer shell and halo. For this work there was data available from ESO (direct imaging and long slit spectroscopy) and from SAAO (spectroscopic observations using a small slit - scanning over the whole nebula). Using temperature measurements from emission lines resulted in an electron temperature which clearly indicates a fully ionized stage. Additionally measurements of the electron density suggest a variation of the filling factor.