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Constraints on Transit Depth Variations of Known Exoplanets with TESS

Presentation #315.02 in the session Catching Big Air (Giant Exoplanet Atmospheres) (iPosters).

Published onOct 20, 2022
Constraints on Transit Depth Variations of Known Exoplanets with TESS

The Transiting Exoplanet Survey Satellite (TESS), although designed to discover new exoplanets, can offer equally if not more valuable insights on the population of known planets. As an ultra-precise photometer, TESS can study in close detail commonly found yet not fully understood phenomena such as exoplanet transit depth variations over time. Specifically, depths have been found to vary on a transit-to-transit basis, and currently there are two main hypotheses for such variation. The first is that by-instrument and by-observer differences are responsible for discrepant transit depths between different authors/instruments, while the second points to astrophysical behavior such as stellar or atmospheric variability as the cause. To study this phenomenon, we first identified 28 known planets, which were selected through a holistic consideration of multiple factors advantageous to the study of transit depth variations, including: a short orbital period, a large transit depth (large planet-to-star ratio), and observation through TESS’s two-minute cadence observing mode in more than one sector. All transits for each planet were then fitted individually through juliet. Two separate analyses were performed on the obtained transit depths, with the first being a model comparison between a GP fit and a horizontal fit to the transit depths, and the second a chi-square test with null hypothesis being that the transit depths remain stable over time. In both cases, our results support that there is no inherent variability in the depth for any of the transiting planets. This is also true in the particular case of WASP-121b, for which Wilson et al. 2021 observed variability in the transit depths through ground-based observations and offered atmospheric variability as a possible—but not certain—explanation. Hence, our results suggest that the differences arise from instrumental rather than astrophysical reasons. Finally, even in the case that changes in the transit depth are indeed astrophysical, or at least partly so, we calculate the standard deviation of the transit depths for each planet, thus placing absolute constraints on the amount by which the transit depth can vary due to such factors. We will next expand on our work by repeating these analyses on a much larger sample of known planets.

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