Near-Infrared Coronagraphic Observations of the T Tauri Binary System UY Aur

We present a near-infrared image of UY Aur, a 0.9″ separated binary system, using the Coronagraphic Imager with Adaptive Optics on the Subaru Telescope. Thanks to adaptive optics, the spatial resolution of our image was ∼0.1″ in the full width at half-maximum of the point-spread function, the highest achieved. By comparison with previous measurements, we estimated that the orbital period is ∼1640 ± 90 yr and the total mass of the binary is ∼1.73 ± 0.29 M⊙. The observed H-band magnitude of the secondary varies by as much as 1.3 mag within a decade, while that of the primary is rather stable. This inconstancy may arise from photospheric variability caused by an uneven accretion rate or from the rotation of the secondary. We detected a half-ring-shaped circumbinary disk around the binary with a bright southwestern part but a barely detectable northeastern portion. The brightness ratio is ≳57 ± 5. Its inner radius and inclination are about 520 AU and 42° ± 3°, respectively. The disk is not uniform but has remarkable features, including a clumpy structure along the disk, circumstellar material inside the inner cavity, and an extended armlike structure. The circumstellar material inside the cavity probably corresponds to a clump or material accreting from the disk onto the binary. The armlike structure is part of the disk, created by accretion from the outer region of the disk or encounters with other stellar systems.