Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): Dynamical Evidence of a Spiral-Arm-Driving and Gap-Opening Protoplanet from SAO 206462 Spiral Motion

TL;DR

This study uses multi-epoch high-resolution imaging to measure spiral arm motion in the SAO 206462 disk, providing dynamical evidence for a protoplanet at 66 au that drives the observed spiral structures and possibly creates the disk gap.

Contribution

First direct measurement of spiral arm rotation in a protoplanetary disk, linking spiral motion to a specific protoplanet candidate at 66 au.

Findings

Measured spiral rotation rate of -0.85°/yr.

Identified a protoplanet candidate at 66 au.

Correlated spiral motion with disk gap and dust filament.

Abstract

In the early stages of planetary system formation, young exoplanets gravitationally interact with their surrounding environments and leave observable signatures on protoplanetary disks. Among these structures, a pair of nearly symmetric spiral arms can be driven by a giant protoplanet. For the double-spiraled SAO 206462 protoplanetary disk, we obtained three epochs of observations spanning 7 yr using the Very Large Telescope's SPHERE instrument in near-infrared $J$-band polarized light. By jointly measuring the motion of the two spirals at three epochs, we obtained a rotation rate of $-0.85^\circ\pm0.05^\circ~{\rm yr}^{-1}$. This rate corresponds to a protoplanet at $66\pm3$ au on a circular orbit dynamically driving both spirals. The derived location agrees with the gap in ALMA dust-continuum observations, indicating that the spiral driver may also carve the observed gap. What is more, a dust filament at $\sim$63 au observed by ALMA coincides with the predicted orbit of the spiral-arm-driving protoplanet. This double-spiraled system is an ideal target for protoplanet imaging.