SCExAO/CHARIS Near-IR High-contrast Imaging and Integral Field Spectroscopy of the HIP 79977 Debris Disk

We present new, near-infrared (1.1-2.4 mu m) high-contrast imaging of the bright debris disk surrounding HIP 79977 with the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) coupled with the CHARIS integral field spectrograph. SCExAO/CHARIS resolves the disk down to smaller angular separations of (0.'' 11; r similar to 14 au) and at a higher significance than previously achieved at the same wavelengths. The disk exhibits a marginally significant east-west brightness asymmetry in H band that requires confirmation. Geometrical modeling suggests a nearly edge-on disk viewed at a position angle of similar to 114 degrees 6 east of north. The disk is best-fit by scattered-light models assuming strongly forward-scattering grains (g similar to 0.5-0.65) confined to a torus with a peak density at r(0) similar to 53-75 au. We find that a shallow outer density power law of alpha(out) = -1 to -3 and flare index of beta = 1 are preferred. Other disk parameters (e.g., inner density power law and vertical scale height) are more poorly constrained. The disk has a slightly blue intrinsic color and its profile is broadly consistent with predictions from birth ring models applied to other debris disks. While HIP 79977's disk appears to be more strongly forward-scattering than most resolved disks surrounding 5-30 Myr old stars, this difference may be due to observational biases favoring forward-scattering models for inclined disks versus lower inclination, ostensibly neutral-scattering disks like HR 4796A's. Deeper, higher signal-to-noise SCExAO/CHARIS data can better constrain the disk's dust composition.