A Ring of Warm Dust in the HD 32297 Debris Disk

Abstract

We report the detection of a ring of warm dust in the near-edge-on disk surrounding HD 32297 with the Gemini North Michelle mid-infrared imager. Our N'-band image shows elongated structure consistent with the orientation of the scattered-light disk. The Fν(11.2 μm)=49.9+/-2.1 mJy flux is significantly above the 28.2+/-0.6 mJy photosphere. Subtraction of the stellar point-spread function reveals a bilobed structure with peaks 0.5"-0.6" from the star. The disk is detected out to the sensitivity limit at ~1", and the flux in each lobe is symmetric to within 10%. An analysis of the stellar component of the spectral energy distribution (SED) suggests a spectral type later than A0, in contrast to commonly cited literature values. We fit three-dimensional, single-size grain models of an optically thin dust ring to our image and the SED using a Markov chain Monte Carlo algorithm in a Bayesian framework. The best-fit effective grain sizes are submicron, suggesting the same dust population is responsible for the bulk of the scattered light. The inner boundary of the warm dust is located 0.5"-0.7" (~65 AU) from the star, which is approximately cospatial with the outer boundary of the scattered-light asymmetry inward of 0.5". The addition of a separate component of larger, cooler grains that provide a portion of the 60 μm flux improves both the fidelity of the model fit and consistency with the slopes of the scattered-light brightness profiles. The peak vertical optical depths in our models [~(0.3-1)×10-2] imply that grain-grain collisions likely play a significant role in dust dynamics and evolution. Submicron grains can survive radiation pressure blowout if they are icy and porous. Similarly, the inferred warm temperatures (130-200 K) suggest that ice sublimation may play a role in truncating the inner disk.