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

We present L′-band Keck/NIRC2 imaging and H-band Subaru/AO188+HiCIAO polarimetric observations of the 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 r2-scaled High-Contrast Coronographic Imager for Adaptive Optics (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 the L′ band to be ∼126 mJy arcsec−2 at most. We suggest that the grain temperature of the spiral may be heated up to ∼200 K in order to explain both of the H- and L′-band 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′-band emission. If the central star is only the light source of scattered light, the spiral emission at the L′ 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′-band spiral structure.