Apparent motion of the circumstellar envelope of CQ Tau in scattered light

TL;DR

This paper measures the apparent motion of spiral structures in the protoplanetary disk of CQ Tau using multiepoch observations, revealing a pattern speed inconsistent with a planet at 20 AU, suggesting other factors influence the spiral morphology.

Contribution

The study introduces a novel differential speckle polarimetry technique to estimate spiral pattern speed in CQ Tau's disk over multiple years, providing new insights into disk dynamics.

Findings

Spiral pattern speed is approximately -0.2 degrees per year.

The observed pattern speed is much smaller than expected for a planet at 20 AU.

Disk shadows likely influence the spiral morphology.

Abstract

The study of spiral structures in protoplanetary disks is of great importance for understanding of processes in the disks, including planet formation. Bright spiral arms were detected in the disk of young star CQ Tau by Uyama et al. (2020) in H and L bands. The spiral arms are located inside the gap in millimeter size dust, recovered earlier using ALMA observations (Ubeira Gabellini et al. 2019). To explain the gap, Ubeira Gabellini et al. (2019) proposed the existence of a planet with the semimajor axis of 20 AU. We obtained multiepoch observations of a spiral feature in the circumstellar envelope of CQ Tau in Ic band using a novel technique of differential speckle polarimetry. The observations covering period from 2015 to 2021 allow us to estimate the pattern speed of spiral: $-0.2\pm1.1^{\circ}$/yr (68% credible interval, positive value indicates counter-clockwise rotation), assuming face-on orientation of the disk. This speed is significantly smaller than expected for a companion-induced spiral, if the perturbing body has the semimajor axis of 20 AU. We emphasize that the morphology of the spiral structure is likely to be strongly affected by shadows of a misaligned inner disk detected by Eisner et al. (2004).