Using NASA's TESS Mission to Characterize an Inflated Giant Planet

We report the discovery of TOI-640b from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission, a hot Jupiter orbiting a newly evolved sub-giant star with a period of 5.0039 0:0003 days. Using photometric data collected from TESS, we extracted the light curve to determine a ratio between the radius of the star and the radius of the planet. The stellar radius was determined using the TESS Input Catalog, which combines data from previous all-sky surveys (Stassun et al., 2019). CHIRON, a high-resolution spectrometer primarily used for radial velocity observations, was used to constrain the mass of the planet. We find that TOI-640 is a slightly evolved sub-giant star, with an effective temperature of 6440+140/-130 K, a stellar mass of 1:49+0:13/-0:11 M, and radius of 2:24+0:36/-0:28 R. The planetary companion, TOI-640b, is an inflated planet with a radius of 1.79 +0:31/-0:25 RJ, and a mass of 0:91+0:13/-0:12 MJ. Some Jovian planets located in close-in, highly irradiated orbits are found to have inflated radii compared to predictions from theoretical models (Guillot & Showman, 2002; Fortney et al., 2007). TOI-640b is one of the most highly inflated giant planets detected thus far. The TOI-640 system is well-suited for further observation, due to the potential insight into inflation mechanisms that could result from the study of planets orbiting sub-giant stars, like TOI-640, as sub-giant stars experience an increase in luminosity which may play a role in planetary inflation.Astro 9