Near-Infrared Imaging of a Spiral in the CQ Tau Disk

TL;DR

This study uses near-infrared imaging to analyze a spiral structure in the CQ Tau disk, revealing details about its morphology, possible heating mechanisms, and the nature of its emission without detecting any companion objects.

Contribution

First detailed imaging and modeling of a spiral in the CQ Tau disk across multiple infrared bands, providing insights into its thermal and scattering properties.

Findings

Spiral feature traced and modeled from polarimetric and direct imaging data.

Estimated grain temperature of the spiral up to 200 K.

Emission at L'-band may be thermal, scattered, or a combination of both.

Abstract

We present $L^\prime$-band Keck/NIRC2 imaging and $H$-band Subaru/AO188+HiCIAO polarimetric observations of CQ Tau disk with a new spiral arm. Apart from the spiral feature our observations could not detect any companion candidates. We traced the spiral feature from the $r^2$-scaled HiCIAO polarimetric intensity image and the fitted result is used for forward modeling to reproduce the ADI-reduced NIRC2 image. We estimated the original surface brightness after throughput correction in $L^\prime$-band to be $\sim126$ mJy/arcsec$^2$ at most. We suggest that the grain temperature of the spiral may be heated up to $\sim$200 K in order to explain both of the $H$- and $L^{\prime}$-bands results. The $H$-band emission at the location of the spiral originates from the scattering from the disk surface while both scattering and thermal emission may contribute to the $L^{\prime}$-band emission. If the central star is only the light source of scattered light, the spiral emission at $L^\prime$-band should be thermal emission. If an inner disk also acts as the light source, the scattered light and the thermal emission may equally contribute to the $L^\prime$-band spiral structure.