# # Program information file # PROGRAM_ID 2023B039 PROGRAM_TITLE Time-dependent dust heating and reverberation in the disk of the highly accreting classical T Tauri star DR Tau PROGRAM_INV1 Peter Abraham PROGRAM_INV2 Agnes Kospal PROGRAM_INV3 Hermine Landt-Wilman PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG The innermost part of the circumstellar disks around young stars, where terrestrial planets form, is a vivid dynamical environment, powered by the accretion process. Synoptic analysis of optical and infrared multi-epoch observations offer new ways to study both the response of the disk to changing stellar irradiation and turbulent structural rearrangements in the disk atmosphere. Here we propose a comprehensive study of the inner circumstellar disk of the highly accreting, highly variable classical T Tauri star DR Tau, based on multi-wavelength time domain spectroscopic information. The SpeX spectrograph is very suitable for such studies, as it can measure both the stellar radiation and the disk's thermal emission simultaneously. In our first science goal we perform a multi-epoch study of the inner disk. We will obtain 0.7-5.3 um spectra at 5 epochs, sampling different brightness states of the star/disk system. We will determine the variations of the accretion rate, the dust temperature, and the emitting surface in the disk. We will check whether higher temperatures coincide with intensified accretion, or a constant temperature but increased infrared flux could be explained by accretion-driven turbulence that enlarges the disk's effective surface. In the second science goal we make a reverberation experiment, one of the first of this kind on a young star. Obtaining SpeX/SXD PRISM spectra with 7 min cadence almost uninterruptedly for 8 hours, we will look for optical brightness fluctuations due to the stellar emission, and search for their reverberation signal in the infrared domain, emitted by dust particles whose temperature changes due to the varying irradiation. The results will help to connect the physics of the accretion and disk changes, and measure in a model-independent way the disk inner radius, one of the most fundamental parameters of the system. PROGRAM_ABSTRACT_END