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

¹ Observatoire de la Côte d'Azur, Dpt. Gemini-CNRS-UMR 6203, Avenue Copernic, 06130 Grasse, France e-mail: Olivier.Chesneau@obs-azur.fr
² Department of Astrophysics, American Museum of Natural History, Cent. Park West 79th Street, New York, NY 10024, USA
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Observatoire de la Côte d'Azur-CNRS-UMR 6202, Dept. Cassiopée, BP 4229, 06304 Nice, France
⁵ Department of Physics and Astronomy, University of Manchester, Sackville street, PO Box 88, Manchester M60 1QD, UK
⁶ Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
⁷ Department of Physics and Astronomy, Louisiana State University Baton Rouge, LA 70803, USA

Received: 24 November 2005
Accepted: 21 May 2006

Abstract

Aims.We present high spatial resolution observations of the dusty core of the Planetary Nebula with Wolf-Rayet central star CPD-56°8032, 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 300 mas resolution and in interferometric mode using UT2-UT3 47m baseline providing a typical spatial resolution of 20 mas. We also made use of unpublished HST/ACS images in the and filters.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-56°8032 is dominated by a compact source, barely resolved by a single UT telescope in a 8.7 μm filter (m, contaminated by PAH emission). The infrared core is almost fully resolved with the three 40–45 m 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  AU, an inclination of and a PA for the major axis at . 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.