Periodic Reporting for period 3 - SACCRED (Structured ACCREtion Disks: initial conditions for planet formation in the time domain)
Berichtszeitraum: 2020-07-01 bis 2021-12-31
Rings also appeared in our hydrodynamic simulations of circumstellar disks. Our modeling revealed the inward motion of these rings, raising the possibility to give a new type of explanation for the origin of protostellar outbursts (Fig. 3). Measuring the time scales of brightening and fading of young stars may reveal a lot about the circumstellar structure and the physics of the eruptions. We are monitoring many FU Orionis-type stars to determine these parameters, and were among the first ones to realize that the accretion of mass onto the protostar V346 Nor temporarily stopped for a short time a few years ago, posing difficult questions to outburst theories. We studied the effect of accretion outbursts on the disk from chemical and mineralogical points of view. We participated in a numerical modeling to predict what chemical reactions are triggered by the outburst heat and on what time scale the disk returns to the quiescent equilibrium. We combined observations with model simulations to follow up a previous result of our group, where we witnessed the crystallization of amorphous dust particles during the outburst of EX Lup. Now we could demonstrate that the fresh crystals were transported outward where they could reach the cold part of the circumstellar disk. We speculate that some crystals might be mixed with ice and form comets, a hypothesis that we will verify with our upcoming observations using the recently launched James Webb Space Telescope.
Based on the results we already achieved, our ongoing projects, and the new ideas we are discussing, my group members and I are enthusiastic about obtaining a significantly clearer picture of the eruptive phenomenon, and make important steps toward defining a new paradigm for it. With the collection of more and more data on the disk structure of both eruptive and non-eruptive young stars, we will try to collect proofs whether eruptive objects follow an extreme evolutionary track or they represent an obligatory period that all young stars need to go through. By the end of the project we will gain more knowledge on the impact of outbursts on the planet forming region, and make a suggestion if eruptions should be taken into account when setting the initial conditions for planet formation models. Our ongoing theoretical study is expected to contribute to the field by proposing a new instability mechanism leading to outbursts, based on a more realistic treatment of disk structure and molecular opacities of the disk material, related to the presence of water molecules. Thus, the expected outcome of the ERC project is a conclusive demonstration of the ubiquity and profound impact of episodic accretion on disk structure, providing the initial physical conditions for disk evolution and planet formation models.