Near-infrared photometry of Galactic planetary nebulae with the VVV Survey

TL;DR

This study utilizes the VVV near-infrared survey to analyze the photometric properties of 353 Galactic planetary nebulae, providing new insights into their colors, emission contributions, and potential for discovering previously unclassified objects.

Contribution

The paper presents the first near-infrared photometry of a large sample of Galactic PNe using VVV data, including diagnostic diagrams and emission analysis, enhancing classification and understanding of PNe in obscured regions.

Findings

H-Ks vs. J-H diagram effectively separates PNe from other objects.

Y band dominated by HeI and HeII lines, sensitive to stellar temperature.

Emission-line contribution varies across bands, highest in Z and Y.

Abstract

Planetary nebulae (PNe) are powerful tracers of evolved stellar populations. Among the 3000 known PNe in the Galaxy, about 600 are located within the 520 square-degree area covered by the VVV survey. The VVV photometric catalogue provides an important new dataset for the study of PNe, with high-resolution imaging in five near-infrared bands. Aperture photometry of known PNe in the VVV area was retrieved from source catalogues. Care was taken to minimise any confusion with field stars. The colours of the PNe we are determined for H-Ks, J-H, Z-Y, and Y-J, and compared to stars and to other types of emission line objects. Cloudy photo-ionisation models were used to predict colours for typical PNe. We present near-infrared photometry for 353 known PNe. The best separation from other objects is obtained in the H-Ks vs. J-H diagram. We calculated the emission-line contribution to the in-band flux based on a model for NGC 6720: we find that this is highest in the Z and Y bands at over 50%, lower in the J band at 40%, and lowest in the H and Ks bands at 20%. A new view of PNe in the wavelength domain of the Z and Y bands is shown. Photo-ionisation models are used to explore the observed colours in these bands. The Y band is shown to be dominated by HeI 1.083 mu and HeII 1.012 mu, and colours involving this band are very sensitive to the temperature of the ionizing star. The VVV survey represents a unique dataset for studing crowded and obscured regions in the Galactic plane. The diagnostic diagrams presented here allow one to study the properties of known PNe and to uncover objects not previously classified.