Program: GN-2018B-Q-232

We propose to measure the obliquity of 19 planet host-stars using high-resolution spectra taken with the GRACES spectrograph with a modest ~5.4h request. Unlike the Solar System, exoplanets have been observed in surprising orbital architectures. The obliquity is a current observable that determines the spin-orbit (mis)alignment and is considered a remnant of the processes involved in the formation and evolution of planetary systems. Previous obliquity measurements have focused on hot Jupiters but little is known of the obliquity of small terrestrial-like planets and/or planets in wider orbits. In an ongoing work, we found that systems composed of 3 or 4 planets (with radii between 0.3 – 4 Earth radius) exhibit only aligned orbits whilst systems with fewer planets may be aligned or misaligned, implying that systems with one or two planets might have different formation and/or evolution history than systems with more planets. In this proposal, we aim to expand multiplanetary systems with measured obliquities from 9 to 22, including terrestrial-like planets. The GRACES observations will enable the exploration of the possible planetary evolutionary pathways for different planet populations.