1. Reconstructing HST Images of Asteroids A. Storrs, S. Bank, H. Gerhardt (Towson Univ.), K. Makhoul (MIT) Acknowledgements: Support for this work provided by NASA through grant GO- 8583 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Abstract: We present reconstructions of images of 22 large main belt asteroids that were observed by Hubble Space Telescope with the Wide-Field/Planetary cameras. All images were restored with the MISTRAL program (Mugnier, Fusco, and Conan 2003) at enhanced spatial resolution. This is possible thanks to the well-studied and stable point spread function (PSF) on HST. We present some modeling of this process and determine that the Strehl ratio for WF/PC (aberrated) images can be improved to 130%, while WFPC-2 images can achieve a Strehl ratio over 80% after reconstruction. We report sizes, shapes, and albedos for these objects, as well as any surface features. Images taken with the WFPC-2 instrument were made in a variety of filters so that it should be possible to investigate changes in mineralogy across the surface of the larger asteroids in a manner similar to that done on 4 Vesta by Binzel et al. (1997). Of particular interest are a possible water of hydration feature on 1 Ceres (see figure), and the non- observation of a constriction or gap between the components of 216 Kleopatra. References: Mugnier, L.M., T. Fusco, and J.-M. Conan, 2003. JOSA A (submitted) Binzel, R.P., Gaffey, M.J., Thomas, P.C., Zellner, B.H., Storrs, A.D., and Wells, E.N. 1997. Icarus 128 pp. 95-103 Krist, J. 1993. The Tiny Tim User’s Manual, Space Telescope Science Institute Image Restoration: Normal astronomical deconvolution processes do not work well on extended objects with sharp brightness variations, such as asteroids. These deconvolution processes will tend to over-enhance the edges of such sources, and so here we have used the MISTRAL routine (Mugnier et al. 2003) to avoid this problem. WFPC-2 images of the asteroids were restored with a theoretical (TinyTim, Krist 1993) PSF. The resultant images have a four times resolution improvement over the unrestored images. The above images demonstrate the technique. The top row contains the unrestored images, and the second row the results of optimal MISTRAL restoration. Both log stretched and oblique surface plots of each image are shown. The left group is an image of a standard star taken with the WF/PC (aberrated) camera, and the right group is taken with the WFPC-2 camera (F439W filter). The Strehl ratio for the WF/PC images is 50% before correction, and 180% after. For WFPC-2, the reconstruction process does not improve the Strehl ratio (about 85% in this image) but does sharpen the image and lower the background level. Note companion star in WFPC-2 image. 11 Parthenope RawRestored S – type Distance from Earth: 1.39 AU Diameter: 162 km Shape: spherical Albedo: 0.15 144 Vibilia Raw Restored C – type Dist. from Earth: 1.20 AU Diameter: 146 km Shape: irregular Albedo: 0.059 89 - Julia RawRestored S – type Distance from Earth: 1.34 AU Diameter: 159 km Shape: irregular Albedo: 0.16 8 - Flora Restored S – type Distance from Earth: 0.90 AU Diameter: 141 km Shape: irregular Albedo: 0.22 Raw 1220 - Crocus RawRestored Unknown Distance from Earth: 2.05 AU Diameter: unknown Shape: irregular Albedo: unknown 10 - Hygiea RawRestored C – type Distance from Earth: 2.54 AU Diameter: 429 km Shape: spherical Albedo: 0.075 29 - Amphitrite RawRestored S – type Distance from Earth: 4.44 AU Diameter: 219 km Shape: irregular Albedo: 0.16 54 - Alexandra RawRestored C – type Distance from Earth: 1.27 AU Diameter: 171 km Shape: spherical Albedo: 0.050 1 - Ceres C – type Distance from Earth: 1.94 AU Projected size 880 x 890 km Shape: spherical Albedo: 0.10 RawRestored Ratio 2:5 Ratio 1:2 Ratio 1:2 – F439W/F673N filter- Blue Continuum Slope Ratio 2:5 – F673N /F791W filter- Water of Hydration Map WFPC-2 Images: 5 - Astraea Visit #1 RawRestored Visit #2 S – type Dist. from Earth: 2.07 AU Diameter: 125 km Shape: spherical Albedo: 0.14 46 - Hestia RawRestored P – type Dist. from Earth: 1.63 AU Diameter: 131 km Shape: spherical Albedo: 0.046 93 - Minerva RawRestored C – type Dist. from Earth: 1.99 AU Diameter: 146 km Shape: spherical Albedo: 0.085 18 - Melpomene RawRestored S – type Dist. from Earth: 1.87 AU Diameter: 148 km Shape: spherical Albedo: 0.22 46 - Pales RawRestored C – type Dist. from Earth: 2.58 AU Diameter: 154 km Shape: spherical Albedo: 0.051 RawRestored 121 - Hermione C – type Dist. from Earth: 2.31 AU Diameter: 217 km Shape: spherical Albedo: 0.042 38 - Leda RawRestored C – type Dist. from Earth: 1.38 AU Diameter: 120 km Shape: spherical Albedo: 0.058 375 - Ursula RawRestored C – type Dist. from Earth: 2.49 AU Diameter: Unknown Shape: spherical Albedo: 0.042 51 - Nemausa RawRestored G – type Dist. from Earth: 1.53 AU Diameter: 153 km Shape: spherical Albedo: 0.086 WF/PC Images: The figure to the right shows the results of running MISTRAL on an extended image. The test image is on the left, convolved with WF/PC (aberrated) PSF in the center, and after restoration with MISTRAL on the right. 9-Metis 18-Melpomene 19-Fortuna 216-Kleopatra 624-Hektor S-type R=2.32 AU,  =1.49 AU Projected size 222x182 km Albedo 0.108 S-type R=2.22 AU,  =1.26 AU Projected size 155x170 km Albedo 0.155 G-type R=2.30 AU,  =1.53 AU Projected size 225x205 km Albedo 0.028 M-type R=3.24 AU,  =2.38 AU Projected size 238x121 km Albedo 0.062 D-type R=5.24 AU,  =4.33 AU Projected size 363x207 km Albedo 0.024 Apparent rotation of 216 Kleopatra during observations. Apparent rotation of 624 Hektor during observations.