# # Program information file # PROGRAM_ID 2024A052 PROGRAM_TITLE JWST-based systematic investigation of disk dynamics in young stars via mid-infrared variability PROGRAM_INV1 Peter Abraham PROGRAM_INV2 Agnes Kospal PROGRAM_INV3 Jozsef Varga PROGRAM_INV4 Lei Chen PROGRAM_INV5 Foteini Lykou PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Optical and infrared variability is a defining characteristics of young stellar objects [YSOs]. During its first year, JWST/MIRI obtained high quality medium-resolution spectra of a number of YSOs. We downloaded all publicly available, pipeline-reduced YSO spectra, compared them with Spitzer IRS spectra, and found that 28 out of 35 studied objects [80%] exhibited significant flux changes in the spectrum. The otherwise similar low-mass T Tauri stars exhibited a variety of variability patterns in particular at shorter wavelengths, around 5 micrometer. It implies ongoing dynamical processes in the inner disk, and the wavelength dependence of the variability is connected to the physical process. Time-dependent stellar irradiation would produce correlated optical-infrared light curves on daily-weekly timescales, while longer timescales imply internal dynamical processes in the inner disk, such as orbiting inhomogeneities or the puffing up of the inner edge of the dust disk. In order to explore further this finding, we initiated a novel systematic investigation of the mid-infrared variability of YSOs. We selected in total 8 targets, 4 proposed here, and perform spectroscopic monitoring with a monthly cadence, using for top infrared instruments: VLT/VISIR and VLTI/MATISSE at ESO, MIRI on JWST, and SpeX at IRTF. We will document the variability trends in the 1-5 micrometer domain, then determine timescales and the physical origin of the flux changes. Our proposed characterization of the spectral variability on monthly timescales - where most likely the variability arises - with IRTF will be a new territory. The variability observed with SpeX will be interpreted in terms of disk physics using a radiative transfer modelling, which will aim to explain the IRTF, JWST, VISIR, and MATISSE observations together. Our project will be a new important step in the systematic investigation of the dynamics of the terrestrial planet forming inner disk in YSOs. PROGRAM_ABSTRACT_END