External or internal companion exciting the spiral arms in CQ Tau?

TL;DR

This study uses high-contrast near-infrared imaging to investigate the presence of companions in CQ Tau's protoplanetary disc, detecting spiral arms and shadows, and constraining the mass of potential unseen companions.

Contribution

The paper provides new high-contrast imaging data of CQ Tau, revealing spiral structures and shadows, and constrains the mass of potential companions, suggesting an unseen close-in companion as a possible cause.

Findings

Detected four spiral arms and a double-arc in the disc.

Ruled out giant planets above 4 M_Jup outside 60 au and above 2-3 M_Jup beyond 100 au.

Evidence suggests a possible unseen close-in companion affecting disc morphology.

Abstract

We present new high-contrast images in near-infrared wavelengths ($\lambda$ = 1.04, 1.24, 1.62, 2.18 and 3.78$\mu$m) of the young variable star CQ Tau, aiming to constrain the presence of companions in the protoplanetary disc. We reached a Ks-band contrast of 14 magnitudes with SPHERE/IRDIS at separations greater than 0."4 from the star. Our mass sensitivity curve rules out giant planets above 4 M$_{\rm Jup}$ immediately outside the spiral arms at $\sim$60 au and above 2-3 M$_{\rm Jup}$ beyond 100 au to 5$\sigma$ confidence assuming hot-start models. We do, however, detect four spiral arms, a double-arc and evidence for shadows in scattered light cast by a misaligned inner disc. Our observations may be explained by an unseen close-in companion on an inclined and eccentric orbit. Such a hypothesis would also account for the disc CO cavity and disturbed kinematics.