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==> This proposal requests an upgrade from Priority 3 for APENNY.AJP_GLOB
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Why is there so little dust in globular clusters?
ISO raster maps of the central 6x16 arcmin of four clusters, with a detection
limit of 1E-4 solar masses of dust (50 times better than the IRAS Surveys),
will either detect dust in these clusters, or give new lower limits. Looking
at clusters of differing masses, metallicities, and differing heights from the
Galactic plane, it is hoped to discriminate between the different mechanisms
proposed to account for fact that there is much less dust than expected.
In the 1E7 years since a typical cluster last crossed the galactic plane
(when all the dust would be stripped out) its stars will have ejected 0.1
solar masses of dust. The dust should be at about 50K, so observations at 50
to 100 microns are needed. (Observations at other wavelengths only give higher
upper limits.) Pointed IRAS observations of 47 Tuc found 4E-4 solar masses and
the IRAS surveys only found higher upper limits for other clusters. Dust is
being removed from clusters, on a timescale of 1E4-1E5 years. With only the
47 Tuc detection, we can neither say if its 3E-4 solar masses of dust is
typical, nor discriminate between the different proposed stripping mechanisms.
ISO is already doing 18000s of Priority 2 time on this project. A further
18000s was allocated at Priority 3. This proposal is to upgrade that Priority
3 time to Priority 2. This is needed both to allow for the fact that the
observing sensitivity is lower than estimated before launch, and also to use
the extended mission lifetime so that the time originally allocated to
Priority 3 can in fact be carried out.
The original proposal has been adapted following new information from our
ISO observations of 47 Tuc, from new knowledge of the cluster orbits from
astrometry, and from new millimetre observations of M 3 and M 22.