Infrared high spatial resolution study of the PN hen 2-113

We report infrared observations of the planetary nebula Hen 2-113 obtained with VLT/NACO, VLTI/MIDI, VLT/ISAAC and TIMMI at the ESO 3.6m. Hen 2-113 exhibits a clear ring-like structure superimposed to a more diffuse environment visible in the L′ (3.8 μm), M′ (4.78 μm) and 8.7 μm bands. No clear core at 8.7 μm and no fringes through the N band could be detected for this object with MIDI. A qualitative interpretation of the object structure is proposed using a diabolo-like geometrical model. Our ISAAC and TIMMI observations indicate that the PAHs are mostly concentrated towards the lobes of the diabolo and the bipolar lobes of the nebula. In L′ band, a void 0.3″ in diameter was discovered with NACO around the central source. The L′ and M′ fluxes from the central source were derived from NACO data indicating an important infrared excess with respect to the expected stellar emission based on stellar models and short wavelength data. The observed flux from this source in the L′ and M′ is about 300 and 800 times higher, respectively, than those expected from a model including only the central star. Moreover, the central object appears resolved in L′ band with measured FWHM about 155 mas. This infrared excess can be explained by emission from a cocoon of hot dust (T∼900K) with a total mass ∼ 10-9M ⊙. © 2005 American Institute of Physics.