IMAGING THE DEBRIS DISK OF HD 32297 WITH A PHASE-MASK CORONAGRAPH AT HIGH STREHL RATIO

Abstract

We present the first Ks-band image of the scattered light from HD 32297's debris disk. HD 32297 is an A5 star known to possess a nearly edge-on disk with a high fractional luminosity Ld/L⋆ ≈ 0.003 in the infrared. Our image was obtained using phase-mask coronagraphy on the 1.6 m well-corrected subaperture on the 5 m Palomar Hale telescope, and reaches an inner working angle of 400 mas. We confirm the previously reported disk asymmetry and central hole. The gray J − Ks disk color appears similar on the two sides of the disk, which would demand a minimum grain size of at least a few microns, larger than thermal arguments suggest. One possible explanation is a planetesimal clump in a resonant orbit with an outward migrating giant planet, located at larger radii than the warm dust emitting at longer wavelengths. Our observations also clearly demonstrate the benefits of operating in the extreme adaptive optics regime with a coronagraph able to reach a very small inner working angle.