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==> In this proposal, more time is being requested for MMEIXNER.PROP_TDH
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We propose to obtain linear scans of the thermal emission from dust in
two planetary nebulae (IC 418 and NGC 7293) and three proto-planetary
nebulae (GL 618, GL 915 and IRAS18184-1623).  Our strategy is to use
the the ISOPHOT FIR arrays, C100, and C200  to image these nebulae at
wavelengths greater than 100 um.  The two goals of these observations
is (1) to determine the history of mass loss as imprinted on the
circumstellar dust envelopes in these PPNe and PNe, and (2) to measure
the total mass of the circumstellar dust from which we can infer a
lower limit to the initial mass of the progenitor main sequence star.
In particular, the radial profiles of dust density derived from these
observations will test current theories of episodic mass loss and
accelerated mass loss.  Understanding this mass loss process is a key
problem within astrophysics because most of interstellar dust and gas
originates from these stellar sources.  ISO provides the necessary
sensitivity and longer wavelength coverage to detect the ~35K thermal
dust halos surrounding PPNe and PNe.