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

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 $\sim 126$ 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.

accepted for publication in AJ