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

¹ Observatorio Astronómico Córdoba, Universidad Nacional de Córdoba, X5000BGP Cordoba, Argentina
e-mail: walter@mail.oac.uncor.edu
² Instituto de Astrofísica de La Plata, CCT La Plata-CONICET, Universidad Nacional de La Plata, Paseo del Bosque s/n 1900, Argentina
e-mail: rgamen@fcaglp.unlp.edu.ar
³ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁴ Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL, UK
⁵ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Casilla 306, Santiago 22, Chile
e-mail: dante@astro.puc.cl
⁶ Vatican Observatory, V 00120 Vatican City State, Italy
⁷ Departamento de Ciencia Fisicas, Universidad Andres Bello, Republica 440 2 do Piso Santiago, Chile
⁸ Instituto de Astronomía Teórica y Experimental, X5000 BGP Cordoba, Argentina

Received: 3 October 2012
Accepted: 20 February 2013

Abstract

Context. 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.

Aims. There are various colour-colour diagrams that can be obtained from the VVV filters. We investigate the location of PNe in these diagrams and the separation from other types of objects. This includes the new Y−J vs. Z−Y diagram.

Methods. 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−K_s), (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.

Results. We present near-infrared photometry for 353 known PNe. The best separation from other objects is obtained in the (H−K_s) 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 K_s 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 He i 1.083 μm and He ii 1.012 μm, and colours involving this band are very sensitive to the temperature of the ionizing star.

Conclusions. The VVV survey represents a unique dataset for studying 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.