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==> OTAC SOLICITED PROPOSAL
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Note: The project is an OTAC solicited proposal. The data will be made
public within 1 month of despatch from ESA on the public ftp/www server
of the ISO SOC.
One of the exciting discoveries made using IRAS was the dust disc
around Vega and other evolved stars. So far, only Beta Pic has had its
disc confirmed optically. Due to the low spatial resolution of IRAS,
relatively  little is known about the immediate environment of Beta Pic
in the infrared. ISOPHOT is being used to make oversampled maps (PHT32 at
60um and 90um, H. Walker et al), as well as for long wavelength photometry
and low resolution spectroscopy.
The reduction of the OTF from 10 to 2 arcsec has made high resolution
scans possible. Recently the P3 detector was used to scan Vega at 60um,
using an aperture below the diffraction limit and with a very small step
size, giving a high resolution scan across the disc. This showed the extent
of the disc very clearly when compared to the point source Gamma Dra
(HR6705). This new observing technique, resulting from ISO's excellent
pointing accuracy, means that the Airy disc can be sampled with around
7 to 8 positions across it, revealing the extended dust disc with ease.
We propose to use this method on Beta Pictoris at 25 and 60 microns to
perform 4 scans across Beta Pic using the P3 detector as indicated above
and 8 scans using the P2 detector at 25 microns.  We also request
the identical scan pattern to be repeated across Gamma Dra (HR6705),
for confirmation of the behaviour of the detector for a genuine point
source (from the influence of the tripod).