http://arxiv.org/abs/2304.12028
Circumbinary discs around evolved post-asymptotic giant branch (post-AGB) binary systems show many similar properties to protoplanetary discs around young stars. Deficits of near-infrared (near-IR) flux in the spectral energy distributions (SEDs) of such systems hints towards large dust-free cavities, reminiscent of transition discs as commonly observed around young stars. We aim to assess the inner rim size of 6 post-AGB binary systems with such a lack in near-IR using resolved mid-IR high-angular resolution observations of VLTI/MATISSE and VLTI/MIDI. The inner rim of only one such system was previously resolved. We compare these inner rim sizes to 5 systems with available MATISSE data that were identified to host a disc starting at the dust sublimation radius. We used geometric ring models to estimate the inner rim sizes, the relative flux contributions of the star, the ring, and an over-resolved emission, the orientation of the ring, and the spectral dependencies of the components. We find that the dust inner rims of the targets with a lack of near-IR excess in their SEDs are 2.5 to 7.5 times larger than the theoretical dust sublimation radii while the systems that do not show such a deficit have inner rim sizes similar to their dust sublimation radii. Physical radii of the inner rims of these transition discs around post-AGB binaries are 3-25 au, which are larger than the disc sizes inferred for transition discs around young stars with VLTI/MIDI. This is due to the higher stellar luminosities of post-AGB systems compared to young stars, implying larger dust sublimation radii and thus larger physical transition disc inner radii. With mid-IR interferometric data we directly confirm the transition disc nature of six discs around post-AGB binary systems. Future observational and modelling efforts are needed to progress on the structure, origin, and evolution of these transition discs.
A. Corporaal, J. Kluska, H. Winckel, et. al.
Tue, 25 Apr 23
18/72
Comments: accepted for publication in A&A. 13 pages, including appendices