AAS 196th Meeting, June 2000
Session 26. The Galactic ISM: Observations and Modelling
Display, Tuesday, June 6, 2000, 10:00am-6:30pm, Empire Hall South

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[26.16] X-Ray Halos and Large Grains in the Diffuse Interstellar Medium

A.N. Witt (University of Toledo), R.K. Smith (HEAD, SAO), E. Dwek (NASA GSFC)

The fraction of metals that is currently locked up in dust is an extremely important astrophysical quantity, yet poorly determined. The total mass of interstellar dust depends critically on the mass fraction of grains with radii larger than about 0.25 \mum. Recent observations with dust detectors onboard the interplanetary spacecraft Ulysses and Galileo have recorded a substantial flux of interstellar grains with radii between 0.25 and 2.0 \mum entering the solar system from the local interstellar cloud. To investigate whether this population of larger dust particles prevails in the general interstellar medium we examined their effect on the intensity and profile of the x-ray scattering halo around Nova Cygni 1992. The results of our study confirm the need to extend the interstellar grain size distribution in the direction of this source to 2 \mum. The augmentation of the previously accepted general interstellar dust population with such larger particles may increase the interstellar dust-to-gas ratio above the accepted Galactic average, further exascerbating the so-called interstellar abundance crisis. The degree of increase in the dust-to-gas ratio depends on assumptions regarding the line-of-sight distribution of the dust. Additional observations of x-ray halos probing other spatial directions are badly needed to test the general validity of these results.

The author(s) of this abstract have provided an email address for comments about the abstract: awitt@dusty.astro.utoledo.edu

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