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ACS Multiband Coronagraphic Imaging of the Debris Disk around ß Pictoris

ACS Multiband Coronagraphic Imaging of the Debris Disk around ß Pictoris. David Golimowski. STScI/NRDD 19 Oct 2005. Collaboration. Observations part of HST/ACS GTO debris disk coronagraphic imaging program

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ACS Multiband Coronagraphic Imaging of the Debris Disk around ß Pictoris

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  1. ACS Multiband Coronagraphic Imaging of the Debris Disk around ß Pictoris David Golimowski STScI/NRDD 19 Oct 2005

  2. Collaboration • Observations part of HST/ACS GTO debris disk coronagraphic imaging program • PI: H. C. Ford (JHU) Deputy PI: G. D. Illingworth (UCSC/Lick Obs.) • GTO Debris Disk Team: Mark Clampin (NASA/GSFC) David Ardila (IPAC/SSC) John Krist (JPL) David Golimowski (JHU)

  3. Motivation • Only two multiband scattered-light imaging studies of ß Pic’s disk have been published: • Paresce & Burrows (1987) • Lecavelier des Etangs et al. (1993) • Ground-based measurements consistent with neutral colors and amin >> 1 µm, but errors are large (15-30%) • Better colors may better constrain grain properties • HST SM-3B: ACS/HRC equipped with high-contrast Lyot coronagraph with broadband filter set

  4. ACS GTO observations of ß Pic • HRC coronagraph images taken in Cycle 12 • 0".9 radius occulting spot • Short & long exps. in F435W (B), F606W (Broad V), F814W (Broad I) • 1 orbit/filter X two orients • Similar images of  Pic (A7 IV) taken for PSF reference

  5. PSF-subtracted images

  6. PSF-deconvolved images

  7. Ratio of images before & after PSF deconvolution

  8. Morphology and Brightness • Inner “warp” is clearly resolved as secondary disk inclined by ~5º to outer disk. Supports notion that giant planet has perturbed planetesimals from main disk into a coplanar orbit. • The main disk (r < 120 AU) has FWHM ~ 11-13 AU, i.e., ~50% narrower than previously measured. PSF deconvolution is crucial for accurate modeling of the disk. • The radial surface-brightness profiles of the main and secondary disks are not alike.

  9. Single power-law fit of secondary disk suggests: • No depletion of dust down to 80 AU • Smaller/larger ice-sublimation zone than main disk

  10. Midplane Colors Uncertainties are 5-10 times smaller than those of previous studies.

  11. Grain characteristics • We compared the midplane colors to simulated colors of grain distributions with various compositions, porosities, and minimum grain sizes. • r < 120 AU: Colors matched by compact or moderately porous (P < 75%), non-icy grains of astrosil/graphite with amin~ 0.15-0.2 µm  10X smaller than ground-based estimates  Consistent with cometary activity within 120 AU • r > 120 AU: Icy grains with amin increasing from 0.15 µm at 120 AU to perhaps ~2 µm at 250 AU.

  12. Legacy of ACS ß Pic Study Our multiband ACS images are the finest optical images of the inner (30-250 AU) region of ß Pic’s disk obtained to date. These images will not be superseded by TPF and other proposed exoplanet-imaging missions due to tiny FOV. Comparable IR images are expected from JWST if current imaging specs are maintained. Thus, our results will be a standard reference for comparative and theoretical studies of debris disks for at least a decade.

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