Dipper Stars: A Serendipitous Window on the Realm of Planet Formation

Eric Gaidos

Variability is one hallmark of T Tauri stars and this characteristic could be a key to unlock the secrets of inner planet-forming disks. The Kepler mission revealed thousands of diverse planetary systems, and one goal of exoplanet research is a predictive theory relating conditions in a protoplanetary disk to these varied outcomes. But at the distance of the nearest star-forming regions, the inner disks corresponding to the orbits of most planets (<1 au) are unresolved. An alternative approach to studying inner disks is via time-series monitoring, exploiting their variability and using time as a proxy for separation via Kepler's third law. Dimming events, when dust from the disk or planetesimals occults the central star, inform about the structure and dynamics of the disk ((and possible proto-planets)) and can be a probe of the composition of the dust and any accompanying gas. There are many possible underlying mechanisms causing dimming, including accretion streams, disk warps and instabilities, dusty winds, and evaporating planetesimals. and more than one could be operating around a given star. This technique is sensitive to relatively small amounts of dust, making it useful to investigate the later stages of disk evolution and planet formation when disks are clearing. Studies of the grain size, composition, and spatial distribution of the dust, as well as any accompanying gas, can help us trace the subsequent, hitherto hidden steps of planet formation. We are conducting an ongoing multi-wavelength campaign to investigate dipper stars with ground- and space-based telescopes. I describe recent results from that campaign highlighting TESS and a Key Project of the Las Cumbres Observatory Global Telescope, with supporting roles by other, larger ground-based facilities.