Keck/NIRC2 imaging of the warped, asymmetric debris disk around HD32297

Abstract

We present Keck/NIRC2 Ks -band high-contrast coronagraphic imaging of the luminous debris disk around the nearby, young A star HD32297 resolved at a projected separation of r = 0″.3-2″.5 (≈35-280AU). The disk is highly warped to the north and exhibits a complex, "wavy" surface brightness (SB) profile interior to r ≈ 110AU, where the peaks/plateaus in the profiles are shifted between the NE and SW disk lobes. The SW side of the disk is 50%-100% brighter at r = 35-80AU, and the location of its peak brightness roughly coincides with the disk's millimeter (mm) emission peak. Spectral energy distribution modeling suggests that HD32297 has at least two dust populations that may originate from two separate belts, likely at different locations, possibly at distances coinciding with the SB peaks. A disk model for a single dust belt including a phase function with two components and a 5-10AU pericenter offset explains the disk's warped structure and reproduces some of the SB profile's shape (e.g., the overall "wavy" profile, the SB peak/plateau shifts) but more poorly reproduces the disk's brightness asymmetry and the profile at wider separations (r > 110AU). Although there may be alternate explanations, agreement between the SW disk brightness peak and disk's peak mm emission is consistent with an overdensity of very small, sub-blowout-sized dust and large, 0.1-1mm sized grains at 45AU tracing the same parent population of planetesimals. New near-IR and submillimeter observations may be able to clarify whether even more complex grain scattering properties or dynamical sculpting by an unseen planet are required to explain HD32297's disk structure. © 2012. The American Astronomical Society. All rights reserved.