Evidence for Primordial Alignment: Insights from Stellar Obliquity Measurements for Compact Sub-Saturn Systems
Brandon T. Radzom, Jiayin Dong, Malena Rice, Xian-Yu Wang, Samuel W. Yee, Tyler R. Fairnington, Cristobal Petrovich, Songhu Wang
arXiv:2404.06504v1 Announce Type: new
Abstract: Despite decades of effort, the mechanisms by which the spin axis of a star and the orbital axes of its planets become misaligned remain elusive. Particularly, it is of great interest whether the large spin-orbit misalignments observed are driven primarily by high-eccentricity migration — expected to have occurred for short-period, isolated planets — or reflect a more universal process that operates across systems with a variety of present-day architectures. Compact multi-planet systems offer a unique opportunity to differentiate between these competing hypotheses, as their tightly-packed configurations preclude violent dynamical histories, including high-eccentricity migration, allowing them to trace the primordial disk plane. In this context, we report measurements of the sky-projected stellar obliquity ($lambda$) via the Rossiter-McLaughlin effect for two sub-Saturns in multiple-transiting systems: TOI-5126 b ($lambda=1pm 48,^{circ}$) and TOI-5398 b ($lambda=-24^{+14}_{-13} ,^{circ}$). Both are spin-orbit aligned, joining a fast-growing group of just three other compact sub-Saturn systems, all of which exhibit spin-orbit alignment. Our results strongly suggest that sub-Saturn systems are primordially aligned and become misaligned largely in the post-disk phase through violent dynamical interactions inherent to eccentric migration, as appears to be the case increasingly for other exoplanet populations.arXiv:2404.06504v1 Announce Type: new
Abstract: Despite decades of effort, the mechanisms by which the spin axis of a star and the orbital axes of its planets become misaligned remain elusive. Particularly, it is of great interest whether the large spin-orbit misalignments observed are driven primarily by high-eccentricity migration — expected to have occurred for short-period, isolated planets — or reflect a more universal process that operates across systems with a variety of present-day architectures. Compact multi-planet systems offer a unique opportunity to differentiate between these competing hypotheses, as their tightly-packed configurations preclude violent dynamical histories, including high-eccentricity migration, allowing them to trace the primordial disk plane. In this context, we report measurements of the sky-projected stellar obliquity ($lambda$) via the Rossiter-McLaughlin effect for two sub-Saturns in multiple-transiting systems: TOI-5126 b ($lambda=1pm 48,^{circ}$) and TOI-5398 b ($lambda=-24^{+14}_{-13} ,^{circ}$). Both are spin-orbit aligned, joining a fast-growing group of just three other compact sub-Saturn systems, all of which exhibit spin-orbit alignment. Our results strongly suggest that sub-Saturn systems are primordially aligned and become misaligned largely in the post-disk phase through violent dynamical interactions inherent to eccentric migration, as appears to be the case increasingly for other exoplanet populations.