A systematic investigation of the unsteady inner disks in young stars using VLT, VLTI, and JWST

Optical and infrared variability is a defining characteristics of young stellar objects (YSOs). More than a decade after the initial studies by ISO and Spitzer, the sensitivity and stability of the 5-27 micrometer spectroscopic measurements of JWST/MIRI set the stage for large scale systematic investigations of the time-dependent behavior of the inner circumstellar disks, via their variable mid-infrared emission. Indeed, several recent publications of JWST/MIRI spectra of YSOs in the literature noted significant deviations from the Spitzer spectra of the same objects, both in spectral shape and absolute flux level. Here we report on a new comprehensive research program focusing on time-dependent variations of the inner disks, the birthplace of terrestrial planets, in a statistical sample of young stars. First we construct a representative list of YSOs falling in a well-defined brightness range observable by both MIRI and high-angular resolution ground-based facilities, in particular ESO's mid-infrared interferometer MATISSE, and VLT/VISIR. Then we collect existing, or acquire new MIRI and MATISSE observations for possibly all entries of this JWST-MATISSE Joint Catalog, with the goal to have both high spectral resolution and high sensitivity spectroscopy, and spatially resolved interferometric information for them. As a start, we have performed a statistical comparison of a number of published JWST/MIRI spectra from the literature with their Spitzer counterparts, and found a very high fraction (~80%) of them exhibiting significant variations in their mid-infrared emission. In the next step, we will supplement the catalog with existing, and new MATISSE observations from our running ESO programs. Combining these pieces of information, we aim to determine timescales of spectral variability; study the structure of the unsteady inner disk; and follow the presence, location and evolution of crystalline silicate particles. Our project will be a new important step in the systematic investigation of the dynamics of the terrestrial planet forming inner disk in YSOs, and in understanding the origin of their infrared variability. In this talk we summarize the goals and strategy of the project, and present the first results.