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Toward other Solar Systems: the demographics of TESS long-period exoplanets

Presentation #200.02 in the session Plenary 3.

Published onJun 20, 2022
Toward other Solar Systems: the demographics of TESS long-period exoplanets

Current occurrence rate estimates for long-period exoplanets as a function of size are based on Kepler observations of just 200 000 stars. While TESs’ observing strategy initially biased it towards primarily finding short-period planets, now that we are at nearly four years of observations, TESS-discovered exoplanets with period in the tens or hundreds of days are being confirmed at an accelerating pace. An important advantage of TESS over Kepler is the much larger number of stars observed, and the brightness of many of those stars, which uniquely enable mass determinations and detailed orbit characterization of their planets by being amenable to RV measurements and greatly facilitate atmospheric characterization. I will briefly introduce the sample of long-period planets (with periods up to ~350 days) identified and followed up by the TESS Single Transit Planet Candidate working group (which also identifies multiply-transiting long-period planets). Most are giant planets, but a few are smaller than 4 Earth radii. Several already have RV mass and orbit measurements, and we find a wide range of bulk densities for this sample. We also find a tentative tendency towards non-circular orbits. Of particular interest is the comparison between the yield of long-period planet candidates from TESS, and the expected yield of based on occurrence rates obtained from Kepler. I will show and discuss the distributions of our few hundred planet candidates resulting from our search to date, as a function of period, size and host star spectral type. I will focus on planets with period > 50 days, for which Kepler provided mostly upper limits on occurrence rates. The completeness of the search must be quantified before final occurrence rates can be determined, but intriguingly, our yield is nearly a factor of two lower than expected for giant planets in the period > 50 days range. Looking to the future, I will discuss the significant increase in the number of long-period planets that TESS’ extended mission 2 (if approved) will bring, over a wide range of planet sizes and host star properties. The expanded sample will lead to even more detailed and multi-dimensional occurrence rates, which in turn will bring new insights into the formation and evolution of exoplanetary systems that are increasingly similar to our own.

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