Nodal precession of a hot Jupiter transiting the edge of a late A-type star TOI-1518

Abstract

Abstract TOI-1518b, a hot Jupiter around a late A-type star, is one of the few planetary systems that transit the edge of the stellar surface (the impact parameter b ∼ 0.9) among hot Jupiters around hot stars (Cabot et al. 2021, AJ, 162, 218). The high rotation speed of the host star (∼85 km s−1) and the nearly polar orbit of the planet (∼120○) may cause a nodal precession. In this study, we report the nodal precession undergone by TOI-1518 b. This system is the fourth planetary system in which nodal precession is detected. We investigate the time change in b from the photometric data of TOI-1518 acquired in 2019 and 2022 with TESS and from the spectral transit data of TOI-1518b obtained in 2020 with two high-dispersion spectrographs; CARMENES and EXPRES. We find that the value of b is decreasing with db$/$dt = −0.0116 ± 0.0036 yr−1, indicating that the transit trajectory is moving toward the center of the stellar surface. We also estimate the minimum value of the quadrupole mass moment of TOI-1518, J2,min = 4.41 × 10−5, and the logarithm of the Love number of TOI-1518, log k2 = −2.17 ± 0.33, from the nodal precession.