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A. Li (University of Missouri-Columbia)
In 1926--1927, two Dutch physicists -- H.A. Kramers (1894--1952) and R. Kronig (1904--1995) independently derived a relation between the real (dispersive) and imaginary (absorptive) parts of the index of refraction. In 1969, E.M. Purcell (1912-1997), a Nobel Prize laureate, applied this relation to the interstellar medium (ISM) and related the interstellar extinction integrated over wavelength to the total volume of grains in the ISM and derived a lower bound on the dust-to-gas ratio. In this talk, I will demonstrate how the Kramers-Kronig relation can be applied to place constraints on (1) the carrier of the mysterious ``21 micron feature'' (only) detected in 12 protoplanetary nebulae, (2) interstellar grain models in the context of ``subsolar'' abundances, and (3) the hypothesis of ``metallic needles'' as an agent responsible for the 3--8 micron flat extinction (seen both in the Galactic Center and in the Galactic plane regions) which is well above expected from standard interstellar grains models.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.