Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2B005

AU-scale interferometric observations of the circumbinary environment of AK Sco

Gabányi, Krisztina (Konkoly Observatory, Hungary)
Mosoni, László (Konkoly Observatory, Hungary)
Ábrahám, Péter (Konkoly Observatory, Hungary)
Juhász, Attila (Leiden Observatory, The Netherlands)
Moór, Attila (Konkoly Observatory, Hungary)
Csengeri, Tímea (MPIfR, Germany)
Henning, Thomas (MPIA, Germany)
Leinert, Christoph (MPIA, Germany)
Ratzka, Thorsten (Universitaet-Sternwarte München, Gemany)

AK Sco is a pre-main sequence spectroscopic binary consisting of two identical F5V stars. In order to constrain the structure of its circumbinary material, we performed interferometric observations with MIDI, the mid-infrared interferometric instrument at the Very Large Telescope Interferometer. Four measurements on three baselines were analysed, and radiative transfer calculations were performed to predict spectrally resolved visibilities for different geometrical configurations. We found that the 8-13 micron emission was clearly resolved by MIDI, and the spectrally resolved visibilities obtained on the three ~50m baselines suggest similar extent and structure along different position angles. The spectral energy distribution (SED), compiled from our ISO and MIDI observations as well as from archival IRAS, Spitzer and ground-based data, exhibits strong silicate emission features at 10 and 20 micron, and a flat continuum (in vF_v) between 7 and 60 micron. Detailed modeling of the profile of the 10 micron silicate feature revealed a dust composition consisting of almost exclusively small amorphous silicate grains. Modeling different possible circumbinary geometries, we found that a moderately flared, partly self-shadowed (UX Orionis-type) circumbinary disk plus an optically thin halo was consistent with both the SED and the MIDI visibilities. This is the first strong indication for the presence of a small envelope (inner and outer radii 1 and 30 AU, respectively) in the AK Sco system. Furthermore, we present APEX CO-line measurements, and we discuss the evolutionary phase of the system in the light of the observational data and modeling results.

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