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TESS Science Meeting, 2021
In this invited talk from the 2021 Virtual TESS Science Meeting, I review how transit timing variations can be used to derive planetary properties and learn more about the orbital mechanics of exoplanet systems.

DDA Virtual Meeting, 2021
Ultra-short-period planets (USPs) reside interior to the expected truncation radius for a typical T Tauri disk, requiring extra explanations for their current orbital locations beyond simple disk migration. In particular, once a planet migrates close to the disk truncation radius, Type I torques will go to zero or switch direction depending on the stellar and disk conditions, and the result is that the planet is expected to stop migration and become trapped. Smaller planets will become trapped at larger distances exterior to the gap, at odds with the observation correlation that USPs tend to have smaller physical radii (less than 2 Earth radii). In this presentation, we explain how for suitable disk parameters, magnetically-driven sub-Keplerian gas flow in the inner disk can naturally counteract these effects and subsequently produce USPs at their observed orbital radii. The sub-Keplerian gas flow provides a headwind to small planets, providing a strong torque which can overcome the effects of outwards Type I migration in the inner disk. For suitable disk and planet parameters, the torques due to the sub-Keplerian gas flow lead to inwards migration on a rapid timescale. This mechanism plus the variability of T Tauri stars results in a plausible mechanism to take small planets from 0.05 - 0.1 AU to 0.01-0.02 AU, consistent with the currently observed USP properties.

DDA Virtual Meeting, 2020
Ultra-short period planets provide a look at the inner edge of the allowed parameter space for planetary orbits. One particularly intriguing geometry of system containing ultra-short period planets is high multiplicity systems where the ultra-short period planet and the outer planets exist in two different dynamical states. This has manifested in the observational data as a small number of stars hosting systems of tightly packed coplanar inner planets as well as an ultra-short period planet, where the orbit of the latter is misaligned relative to the mutual plane of the former. We describe two different mechanisms that can produce an ultra-short period planet that is misaligned with the rest of its compact planetary system: natural decoupling between the inner and outer system via the stellar quadrupole moment, and decoupling forced by an external companion with fine-tuned orbital parameters. These two processes operate at different timescales, and can thus occur simultaneously or independently within a single system. We use the K2-266 system as an example to illustrate the dynamics of these two processes.

Plain Academic