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   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)

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 a min >> 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

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

PSF-subtracted images

PSF-deconvolved images

Ratio of images before & after PSF deconvolution

Morphology and Brightness  Inner “warp” is clearly resolved as secondary disk inclined by ~ 5 º 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 ~ 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.

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

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

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 a min ~ µm  10X smaller than ground-based estimates  Consistent with cometary activity within 120 AU  r > 120 AU: Icy grains with a min increasing from 0.15 µm at 120 AU to perhaps ~ 2 µm at 250 AU.

Legacy of ACS ß Pic Study Our multiband ACS images are the finest optical images of the inner ( 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 These images will not be superseded by TPF and other proposed exoplanet-imaging missions due to tiny FOV.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.

Optical Colors

Grain characteristics We compared the midplane colors to simulated colors of non-icy grains with various compositions, porosities, and minimum grain sizes.