Figure 1: Coronagraphic polarimetry of GM Aur comparing polarimetry results without (top) and with (bottom) matched PSF-subtraction. Without subtraction of an unpolarized PSF-star, the polarization fraction of the GM Aur disk is diluted by residual instrumentally diffracted and scattered light from the coronagraphicaly occulted (unpolarized) central star. The efficacy of the technique is born out by the essentially identical position angle and polarized intensity images in the right two columns. PSF subtraction enables decoupling the polarization fraction and total intensity (2 mm flux density) with accurate measurements of both (overcoming one of the primary difficulties encountered in ground- based AO polarimetry). These observations are from GO (PI: Schneider). Glenn Schneider (The University of Arizona, Dean C. Hines (Space Science Institute) and the HST/GO & Teams Abstract The formation of planetary systems is intimately linked to the dust population in circumstellar disks, thus understanding dust grain evolution is essential to advancing our understanding of how planets form. While it is well established that stars form in ISM-like protostellar environments, the connection to now observable light-scattering circumstellar disks and the processes of planet formation is still very uncertain. Mid-IR spectral studies suggest that disk grains are growing in the environments of young stellar objects during the putative planet-formation epoch. Structures revealed in well resolved images of older circumstellar debris disks suggest gravitational influences on the disks from putative co-orbital bodies of planetary mass. To further elucidate the dust and systemic properties in potentially planet-forming systems, we have undertaken two symbiotic HST imaging programs that exploit the recently commissioned capabilities of coronagraphic polarimetry with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), probing dust structures in T Tauri circumstellar disks during the early epochs of planet formation, and debris disks around older stars. We present the first observational results from these two programs in light of earlier commission observations of TW Hya, focusing on the scattered light disks around the T Tauri star GM Aur and the debris disk associated with HR 32297, along with optical (ACS) coronagraphic polarimetry of the unusual dust structure around HD Support for this work was provided by NASA through grant numbers GO and from the Space Telescope Science Institute, which is operated by Association of Universities for Research in Astronomy Incorporated, under NASA contract NAS NASA. Coronagraphic Polarimetry of HST-Resolved Circumstellar T Tauri and Debris Disks Figure 2: HST/NICMOS coronagraphic polarimetry of the debris disk associated with HD 32297, originally imaged with NICMOS in total light by Schneider, Silverstone & Hines 2005, ApJ, 629, L117. Polarizations ~20% are measured along the mid-plane of this nearly edge-on disk. 1 Glenn Schneider (PI: University of Arizona), Dean C. Hines (Space Science Institute), Angela S. Cotera (SETI Institute), Francois Menard (Universite de Grenoble), Christophe Pinte (Universite de Grenoble), Karl Stapelfeldt (JPL), Barbara A. Whitney (Space Science Institute) 2 Dean C. Hines (PI: Space Science Institute), Glenn Schneider (University of Arizona), Jean-Charles Augereau (Universite de Grenoble, Dana E. Backman (NASA Ames), Angela S. Cotera (SETI Institute), James R. Graham (UC Berkeley), Paul Kalas (UC Berkeley), Francois Menard (Universite de Grenoble), Stanimir A. Metchev (UCLA), Deborah Padgett (SSC), Dan E. Potter (University of Arizona), Christophe Pinte (Universite de Grenoble), Murray Silverstone (Eureka), Karl Stapelfeldt (JPL), Barbara A. Whitney (Space Science Institute) Optically Thick T-Tauri Disk Scattering Optically Thin Debris Disk Scattering Figure 3: Optical coronagraphic imaging polarimetry of the debris disk associated ~100 Myr old star HD 61005, which is a G9V star at D = 34.6 pc. These optical images were obtained with the Advanced Camera for Surveys (ACS) aboard HST. This extraordinary system was fisrt imaged in total light with NICMOS (Hines et al. 2007, ApJ, 671, L165). The swept morphology appears to be caused by a collision between the debris system and an enhanced density cloud within the interstellar medium. The polarized intensity image reveals a ridge of highly polarized (~30%) light along the putative leading egde of the disk. Total Intensity (I) Polarized Intensity (P*I) Position Angle (  ) Polarization (P) 0˚ 180˚ 0% 100% HD ACS 0.6  m Coronagraphic Polarimetry