Using new observations of HAT-P-13b with the Infrared Array Camera on the Spitzer Space Telescope, Buhler et al. (2016) show that the orbital eccentricity of HAT-P-13b is 0.007 ± 0.001, and this corresponds to an estimated Love number of approximately 0.31. Based on this Love number and the measured radius of HAT-P-13b, interior structure models of HAT-P-13b show that the most probable core mass for HAT-P-13b is 11 times the mass of Earth. Also, the planet’s core mass has a 68 percent probability of being less than 25 times the mass of Earth, and a 95 percent probability of being less than 47 times the mass of Earth. This represents the best measurement to date on the core mass of a hot-Jupiter.
Buhler et al. (2016), “Dynamical Constraints on the Core Mass of Hot Jupiter HAT-P-13b”, arXiv:1602.03895 [astro-ph.EP]