To constrain the physical processes more, we are building and refining the physical model for this target, fitting simultaneously the photometry and the afore mentioned infrared interferometric observations. We developed a methodology to find the family of models that best reproduce the photometric and interferometric features, such as the star-to-disc flux ratio, the radial extents of the different bands and the amount of extended flux captured. We find a set of models that are able to reproduce most of these features. With our strategy, we found that we can constrain some of the disc parameters, such as the scale height parameters (beta and h0), the dust mass, the grain size distribution power law (q), and the presence (or absence) of metallic iron in the disc. One important ingredient is still missing; we cannot fully fit the over-resolved component, which is best seen in the very small baseline fit to the visibilities.

Recently it was discovered that there are indications that 10% of the post-AGB binary systems in our Galaxy host a disc with an inner large cavity in the dust distribution. Such transition discs are also found in young stellar objects. To see whether these post-AGB systems indeed host such discs, we use mid-infrared interferometric observations. I’m the PI of three successful proposals for VLTI/MATISSE data of such discs.
I modelled the obtained data using geometric modelling and resolved the size of the inner dust cavity. I compared those systems to five systems that are expected to host a full disc, based on both photometric properties and previous infrared interferometric observations. Indeed, we show that the six post-AGB systems that were proposed to host a transition disc have inner cavities of 2.5-7.5 times the dust sublimation radius. We therefore confirm the transition disc nature of circumbinary discs around post-AGB binary systems. Future studies need to reveal the structure and origin of these transition discs.