A close look into the carbon disk at the core of the planetary nebula CPD-56°8032

Aims. We present high spatial resolution observations of the dusty core of the Planetary Nebula with Wolf-Rayet central star CPD-568032, for which indications of a compact disk have been found by HST/SITS observations. Methods. These observations were taken with the mid-infrared interferometer VLTI/MIDI in imaging mode providing a typical 300mas resolution and in interferometric mode using UT2-UT3 47m baseline providing a typical spatial resolution of 20mas. We also made use of unpublished HST/ACS images in the F435W and F606W filters. Results. The visible HST images exhibit a complex multilobal geometry dominated by faint lobes. The farthest structures are located at 7 from the star. The mid-IR environment of CPD-568032 is dominated by a compact source, barely resolved by a single UT telescope in a 8.7μm filter (∆λ=1.6μm, contaminated by PAH emission). The infrared core is almost fully resolved with the three 40-45m projected baselines ranging from -5 to 51 but smooth oscillating fringes at low level have been detected in spectrally dispersed visibilities. This clear signal is interpreted in terms of a ring structure which would define the bright inner rim of the equatorial disk. Geometric models allowed us to derive the main geometrical parameters of the disk. For instance, a reasonably good fit is reached with an achromatic and elliptical truncated Gaussian with a radius of 97±11AU, an inclination of 28±7 and a PA for the major axis at 345±7. Furthermore, we performed some radiative transfer modeling aimed at further constraining the geometry and mass content of the disk, by taking into account the MIDI dispersed visibilities, spectra, and the large aperture SED of the source. These models show that the disk is mostly optically thin in the N band and highly flared. As a consequence of the complex flux distribution, an edge-on inclination is not excluded by the data.