New Parameter Measurements for the Ultra-Short-Period Planet TOI-1807b

Abstract: The ultra-short-period (USP) planets are exoplanets with very short orbital periods ($\textit{P} < 1$ day), and TOI-1807b is one such planet recently discovered by the TESS mission where it orbits in the TOI-1807 system that is still little known nowadays. In this paper, we re-analyzed the transit light curves of TOI-1807 using the latest TESS data from Sector 49, combined with previous data from Sector 22 and 23. By running the MCMC simulation through all three sectors, we found that our transit model fits the data from Sector 49 the best, and we deduced that TOI-1807b is a Super-Earth with a mass of $2.27^{+0.49}_{-0.58}\, M_\oplus$, a radius of $1.37^{+0.10}_{-0.09}\, R_\oplus$, a density of $0.875^{+0.264}_{-0.285}\, \rho_\oplus$, and a surface temperature of $1499^{+82}_{-129}\, \mathrm{K}$. We confirmed that TOI-1807b orbits at approximately $0.0135^{+0.0013}_{-0.0022}\, \mathrm{AU}$ with a period of $0.54929^{+0.00012}_{-0.00005}\, \mathrm{days}$, which raises the possibility of the planet being tidally locked due to spin-orbit synchronization. In addition, we suggest that TOI-1807b might slowly undergo its orbital decay process, and we further identify that TOI-1807b is in a circular, synchronous orbit and permanently deformed due to tides, leading to $\sim$4% correction in density. Since TOI-1807 is such a young star with an age of only $300 \pm 80\, \mathrm{Myr}$, we also imply that the radiation emitted from active TOI-1807 could be so intense that it might have destroyed most of the atmosphere over the surface of TOI-1807b.