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We propose a series of studies of an optically thin edge-on disk discovered
around the star BD +31 643 in the open cluster and star-forming region IC 348
by our co-investigator Kalas using visual coronagraph imaging.  This disk is a
large (d > 12000 AU = 40 arcsec) analog to the beta Pic disk, surrounding a
close binary pair of B5 main sequence stars.  The IR properties of this system
are nearly unknown so we are requesting time with all 4 of ISO's instruments.
This 2nd-call proposal is an extension of our ISO program RSTENCEL.VEGADIS.
The new disk is embedded in a 2x3 arcmin reflection nebulosity that is also
powered by the B stars.  The disk has a central region with lower surface
brightness than an inward extrapolation of the outer disk density, similar
in character to the profile of the beta Pic disk (with much larger scale),
indicating a central region of significantly depleted dust density.  The
new disk has optical depth of order 10^-3 to 10^-2, similar to or somewhat
larger than beta Pic's.  The lifetimes of micron-sized grains at the outer
edges of the central zones in the beta Pic and BD +31 643 disks are
substantially shorter than the system ages, indicating that the grain disks
must be continually replenished, perhaps by collisions of planetesimals or
cometary activity.
We plan to test via maps at 3 wavelengths with CAM and PHT whether the color
temperature and IR surface brightness of the disk are symmetric about the B
stars and decrease with radius at rates consistent with expectations for
plausible-sized particles, and whether the central depletion reveals itself
in the spectral energy distribution.  We also plan SWS and LWS spectra in
search of clues to composition and excitation of the disk in reflectance.