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A Potentially Re-inflated Exoplanet Orbiting a Red Giant Star
Daniel Huber (University of Sydney), Samuel Grunblatt (University of Hawaii), Eric Gaidos (University of Hawaii), Benjamin Fulton (University of Hawaii), et al.
While most exoplanet surveys focus on main sequence stars, our understanding of planets orbiting red-giant branch (RGB) stars is limited. Due to their diversity in mass, luminosity, and chemical composition, RGB stars can help tackle unsolved questions in exoplanet science such as the puzzling radius inflation of gas-giant planets. We present first results from our Asteroseismology & Giants Orbiting Giants (AGOG) K2 program, including the discovery of an inflated (~1.4 RJ, ~1.1 MJ) planet in an 8.4 day orbit around a oscillating low-luminosity red giant star. The incident flux on the planet was near the inflation threshold while the star was on the main-sequence, providing tentative support for the proposal by Lopez & Fortney (2015) that post-main sequence stellar evolution can re-inflate planets through direct deposition of energy into the planetary interior.