Confirmation and characterization of Galactic planetary nebulae: insights from a spectroscopic study

TL;DR

This spectroscopic survey targets 25 objects proposed as possible Galactic planetary nebulae to confirm their nature and derive physical/chemical properties. Using long-slit spectra from two 2.1 m telescopes and ANNEB/NEBULAR analyses, the authors confirm eight true PNe via diagnostic diagrams, derive electron temperatures and densities for selected cases, and determine elemental abundances for three objects that align with Galactic PN benchmarks. They find four PNe with $[\mathrm{N II}]\lambda6583$ brighter than $\mathrm{H\alpha}$, with shock excitation explaining at least two instances, and provide angular sizes from $\mathrm{H\alpha}$ and $[\mathrm{O III}]\lambda5007$. The work also addresses misclassifications and emphasizes the need for spectroscopic confirmation to refine the PN census and understand selection biases in modern catalogs.

Abstract

We present a spectroscopic investigation of 25 objects previously reported as possible Planetary Nebulae (PNe) in recent catalogs to obtain their physical properties and to establish their true nature. We found 11 objects showing intense emission lines, 11 where it was not possible to measure $\mathrm{Hβ}$, and three where no lines are present. We have used diagnostic diagrams to confirm the true PN nature for eight objects. We obtained elemental abundances for three objects whose values are in agreement with the PNe mean values for our Galaxy. Four objects show [N II] $λ$6583 more intense than $\mathrm{Hα}$, and for two of them, this can be explained by the presence of shocks in the gas. Finally, we report angular sizes based on $\mathrm{Hα}$ and [O III] $λ$5007 emission.

Figures (9)

• Figure 1:
• Figure 1:
• Figure 2: A $\log F(\mathrm{H{\alpha}})/F([\mathrm{ \hbox{N \smaller\rmfamilyII}}])$ versus $\log F(\mathrm{H{\alpha}})/F([\mathrm{ \hbox{S \smaller\rmfamilyII}}])$ diagnostic diagram. $F([\mathrm{ \hbox{N \smaller\rmfamilyII}}])$ refers to the sum of the flux of $\lambda6548$ and $\lambda6583$ nitrogen lines. $F([\mathrm{ \hbox{S \smaller\rmfamilyII}}])$ refers to the sum of $\lambda6716$ and $\lambda6731$ sulfur lines. All eight objects lie within the PNe region, as indicated by the empirical boundaries from 2010PASA...27..129F. Uncertainties bars are the same size or smaller than the symbols.
• Figure 3: Diagnostic diagrams to distinguish shock-excited and photoionised regions. Top: proposed by 2008AA...489.1141R with the shock region from 2017PASA...34...36A. Bottom: proposed by 2023MNRAS.525.1998M. Photoionization models are in a blue contour, low-velocity shock models with magenta and high velocity shock models with red. Symbols: $\triangle$ PN G047.8+02.4, $\blacktriangle$ PN G073.6+02.8, $\square$ PN G086.2$-$01.2, and $\blacksquare$ PN G077.4$-$04.0. Uncertainties are the same size or smaller than the symbols.
• Figure A1: