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Accounting for Selection Effects in the Kepler and K2 Exoplanet Samples

Presentation #317.05D in the session “Exoplanet Populations: Observations and Demographics”.

Published onJan 11, 2021
Accounting for Selection Effects in the Kepler and K2 Exoplanet Samples

With nearly 4000 known transiting exoplanets, work on understanding the demographics of these candidates can be used to constrain planet formation mechanisms. In order to study these demographics, it is essential that the planet sample is attained through an automated pipeline, which can provide measurements of the sample completeness (the rate of false negatives) and reliability (the rate of false positives). Such automation was achieved with the Kepler space mission, but additional biases exist when considering multi-planet system detections. With a thorough understanding of the sample completeness -and the multiplicity completeness- I developed a forward modeling algorithm able to simulate the selection effects of the Kepler space mission and infer an underlying planet population (ExoMult). In doing so, I was able to provide a more robust measure of the underlying exoplanet multiplicity and mutual inclination distributions. Furthermore, I was able to resolve a well-known discrepancy over the excess of single transiting planets detected by Kepler. Upon the failure of two reaction-wheels on the Kepler space craft, the successor mission, K2, was born. Providing 18 additional fields, across nearly 4% of the total sky, these fields provide a unique opportunity to understand how exoplanet occurrence is affected by Galactic latitude, stellar metallicity, and stellar age. However, the spacecraft systematic issues have made automation and corresponding demographics studies difficult. With the development of the EDI-Vetter suite of signal vetting metrics, optimized to address K2 systematic issues, I created a fully automated pipeline now able to detect and vet transit signals in the K2 data. Creating such a pipeline, I detected 730 planet candidates with nearly 200 previously undetected candidates in the K2 fields. With corresponding measures of sample completeness and reliability now available, demographics work using this data can proceed. Modifying the ExoMult forward modeling software, to address the K2 specific selection effects, I performed the first small transiting planet demographics study outside of the Kepler field, testing the robustness of these results. Overall, I found a minor deficit of planets in the Campaign 5 field of K2 when compared to the Kepler field, indicating a potential effect of stellar metallicity on small transiting planet occurrence.


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