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We present the first near infrared (NIR) spatially resolved images of thecircumstellar transitional disk around SR21. These images were obtained withthe Subaru HiCIAO camera, adaptive optics and the polarized differentialimaging (PDI) technique. We resolve the disk in scattered light at H-band forstellocentric 0.1"<r<0.6" (12<r<75AU). We compare our results with previouslypublished spatially-resolved 880 micron continuum Submillimeter Array (SMA)images that show an inner r<36AU cavity in SR21. Radiative transfer modelsreveal that the large disk depletion factor invoked to explain SR21's sub-mmcavity cannot be "universal" for all grain sizes. Even significantly moremoderate depletions (delta=0.1, 0.01 relative to an undepleted disk) than thosethat reproduce the sub-mm cavity (delta~10^-6) are inconsistent with our H-bandimages when they are assumed to carry over to small grains, suggesting thatsurface grains scattering in the NIR either survive or are generated bywhatever mechanism is clearing the disk midplane. In fact, the radial polarizedintensity profile of our H-band observations is smooth and steeplyinwardly-increasing (r^-3), with no evidence of a break at the 36AU sub-mmcavity wall. We hypothesize that this profile is dominated by an optically thindisk envelope or atmosphere component. We also discuss the compatibility of ourdata with the previously postulated existence of a sub-stellar companion toSR21 at r~10-20AU, and find that we can neither exclude nor verify thisscenario. This study demonstrates the power of multiwavelength imaging oftransitional disks to inform modeling efforts, including the debate overprecisely what physical mechanism is responsible for clearing these disks oftheir large midplane grains.

Mapping H-band Scattered Light Emission in the Mysterious SR21 Transitional Disk