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==> Time for this proposal is to be transferred from RSTENCEL.VEGADIS2
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We request 7.6 hours of supplemental observing time to obtain improved
oversampled PHOT P32-C100 maps of many of the brightest Vega-disk systems not
already included in Central Programmes.  As part of our NASA Key Project
RSTENCEL VEGADIS2, we have obtained ISO maps of 5 of these sources, during
early release observations last spring. In 2 systems, we see evidence for
extended 60 micron emission out to 30" from the stars.  In all cases, the
data obtained have inadequate S/N to provide definitive statements concerning
their disks.  Thus, we propose to reobserve these 5 systems with longer
integration times to improve the S/N, and observe the remaining autumn and
spring sources from RSTENCEL VEGADIS2 with an improved strategy for optimized
S/N results.
With this imaging survey we want to find out: (1) How frequently
Vega-type stars show resolvable extended structures of cool dust, at about
100 AU from the stars. (2) For those systems with definite extended
emission, we want to infer the geometry of the circumstellar dust
distribution. The sample we started to observe (in RSTENCEL VEGADIS2
program) consists of bright (total 60 micron flux greater than 0.5 Jansky)
nearby (closer than 20 parsecs) Vega-type main-sequence stars. IRAS
photometry of these sources show far-infrared excesses, but there are no
IRAS spatially-resolved measurements for the majority of these systems.