2014ApJ...783...21R

We present an adaptive optics imaging detection of the HD 32297 debris disk at L' (3.8 µm) obtained with the LBTI/LMIRcam infrared instrument at the Large Binocular Telescope. The disk is detected at signal-to-noise ratio per resolution element ∼3-7.5 from ∼0.''3 to 1.''1 (30-120 AU). The disk at L' is bowed, as was seen at shorter wavelengths. This likely indicates that the disk is not perfectly edge-on and contains highly forward-scattering grains. Interior to ∼50 AU, the surface brightness at L' rises sharply on both sides of the disk, which was also previously seen at Ks band. This evidence together points to the disk containing a second inner component located at ≲ 50 AU. Comparing the color of the outer (50 <r/AU <120) portion of the disk at L' with archival Hubble Space Telescope/NICMOS images of the disk at 1-2 µm allows us to test the recently proposed cometary grains model of Donaldson et al. We find that the model fails to match this disk's surface brightness and spectrum simultaneously (reduced chi-square = 17.9). When we modify the density distribution of the model disk, we obtain a better overall fit (reduced chi-square = 2.87). The best fit to all of the data is a pure water ice model (reduced chi-square = 1.06), but additional resolved imaging at 3.1 µm is necessary to constrain how much (if any) water ice exists in the disk, which can then help refine the originally proposed cometary grains model.