We put significant effort into discovering and characterizing new eruptions or young stars based on alerts for unexpected brightenings from the Gaia space mission. We used the latest and most powerful astronomical instruments to obtain the sharpest images and most sensitive spectra of the disks around young stars. We used a technology that connects the infrared light from four of the largest telescopes in the world to form a giant mirror. We used millimeter-wave observations to survey the distribution of cold dust grains in ten FU Orionis-type objects using the ALMA antenna array and found that these disks are typically smaller but more massive than disks around normal, noneruptive young stars. In the L1551 IRS 5 system, we managed for the first time to make an image of all components: two circumstellar disks, a circumbinary ring, and streamers of material connecting these structures (Fig.1). In the double-burster Z CMa system, we detected another streamer that seems to point to a hitherto unknown third component, an intruder whose likely fly-by may explain the outbursts (Fig.2). In the disk around V960 Mon, we discovered large dusty clumps that could collapse to create giant planets (Fig. 3).
Rings also appeared in our hydrodynamic disk simulations. Our modeling revealed the inward motion of these rings, providing a new type of explanation for the origin of outbursts (Fig.4). Measuring the timescales of brightening and fading of young stars may reveal much about the circumstellar structure and the physics of the eruptions. We monitored many FU Orionis-type stars to determine these parameters and were among the first to realize that the accretion of mass onto the protostar V346 Nor 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 numerical studies to predict what chemical reactions are triggered by the outburst heat and how the outbursts impact the size of the dust grains in the disk.
We conducted several studies of EX Lup, the prototype of one class of young eruptive stars. We combined observations with model simulations to follow up our previous result where we witnessed the crystallization of amorphous dust particles during the outburst of EX Lup in 2008. Now, we can demonstrate that the new crystals were transported outward. With the exceptional sensitivity of the James Webb Space Telescope, we successfully rediscovered the crystals in the cold parts of the disk. Some of these crystals might be mixed with ice and become parts of forming comets and planets. We also detected molecules that are essential ingredients for the development of life, such as carbon monoxide and water vapor (Fig.5).
