Observing the building blocks of planets in protoplanetary disks

Jozsef Varga, L.B.F.M. Waters, Michiel Hogerheijde, Roy van Boekel, Alexis Matter, Bruno Lopez, Karine Perraut, Carsten Dominik, Lei Chen, Peter Abraham, Agnes Kospal

Rocky planets form by the concentration of solid particles in planet-forming disks. The chemical composition of terrestrial planets reflects the materials available in the disk in solid phase at the time the planets were forming. Observations in the infrared indicate that large part of the circumstellar dust is made of silicate minerals. Other materials, like solid carbon or metallic iron has been also proposed as major dust constituents. The relative abundances of these planetary building blocks will have a big impact on the physical and chemical properties of the forming planets, yet observations are still lacking in this regard. We will show what constraints we can get on the dust composition of planet-forming disks from infrared spectro-interferometric observations. Currently, optical-infrared interferometers have alone the resolving power needed to reach the inner few au disk region, where terrestrial planets can form. VLTI is the best in class for that task, as its instruments work at near- and mid-infrared wavelengths, where the inner disk thermal emission peaks. We developed a novel model to analyse VLTI data on circumstellar disks, in order to constrain the disk structure and dust composition at the same time. Our method is demonstrated for the case of HD 144332, a young star with a well-studied planet-forming disk.