High spatial resolution study of the inner environment around two young planetary nebulae with [WR] central stars

Abstract

We present observations of the dusty emission from the young planetary nebulae Hen 2-113 and CPD-56$^\circ$8032 obtained with VLT/NACO, VLTI/MIDI. Our NACO observations of Hen 2-113 reveals the presence of a diabolo-shaped structure. The L$\prime$ and M$\prime$ flux from the central source, show a strong infrared excess close to the central star and this source is resolved at a scale of about 150 mas. This infrared excess is explained by emission from a cocoon of hot dust with mass $\sim 10^{-9}$ M$_{\odot}$ at $\sim$900 K. The central source is no longer visible with MIDI in the N-band and the nebula is fully resolved by a 8m telescope in this band. The dusty environment of CPD-56$^\circ$8032 is much more compact, dominated by a bright, barely resolved, core whereas visible unpublished HST images shows that the nebula has an amazing complexity. From MIDI 8.7-$\mu$m acquisition images (dominated by PAH emission), the extension and geometry of the core have been estimated. Moreover, high SNR fringes at low level have been detected with projected baselines between 40 and 45 meters. This clear signal is interpreted in terms of the bright inner rim of a dusty disk exposed to the flux from the Wolf-Rayet star. The geometrical parameters of the N-band flux distribution are well constrained by means of simple geometrical models and a simple radiative transfer model has been developed to extract the physical parameters of the disc. The PA angle of the disk agrees well with the HST/STIS observations of De Marco et al. (2002), but the inferred inclination is much less (i$\,{\sim}\,30^\circ$).