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A.B. Schultz (CSC/STScI), H.M. Hart (CSC/JHU), M. Kochte (CSC/STScI), G.F. Bruhweiler, M.A. DiSanti, C. Miskey (IACS/CUA), K.-P. Cheng (CSUF), K. Reinhard (Wesleyan Unv.), G. Schneider (Steward Observatory)
The extreme differences in surface brightness between a central bright star and any surrounding disk material normally precludes direct optical or near-Infrared imaging of the disk. Ground-based coronagraphs and telescope occulting masks have provided a modest capability to detect and study disks. Three instruments onboard the Hubble Space Telescope (HST), the Wide Field and Planetary Camera 2 (WFPC2), the Space Telescope Imaging Spectrograph (STIS), and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), provide imaging opportunities to study disks. A novel WFPC2 observing mode called "Pyramid Imaging" was used during three HST observing cycles to image six bright infrared excess stars. A total of nine stars were imaged, six target stars (\beta Pictoris, \beta Leo, 51~Oph, \epsilon Eri, \alpha CrB, \alpha PsA) and three PSF stars (\alpha Pictoris, \iota Cen, 98~Aqr). Except for the disk about \beta Pictoris, no disk material was optically detected for the other Vega-like stars. Depending upon the target, we reached as close as ~5\arcsec\ with a limiting optical magnitude of 22nd with 0.04\arcsec\ resolution out to 30\arcmin\ from each star in the planetary camera (PC) chip and in the three wide field (WF) chips we reached 0.1\arcsec\ resolution out to 60\arcmin. These observations suggest that the disk material is possibly confined to a few tens of AU from the stars, the optical scattering is small, or the density of particles is too low to detect them with optically scattered light. The WFPC2 Pyramid Imaging technique, though it failed to provide the capability to optically detect these disks, provided imaging across large fields adjacent to the stars.
Support for this work provided by by NASA through HST/GO grants GO-06058.01-94A and GO-0649.01-95A.
The author(s) of this abstract have provided an email address for comments about the abstract: schultz@stsci.edu