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Session 35 -- ISM: Abundances and Dust
Display presentation, Wednesday, June 14, 1995, 9:20am - 6:30pm

[35.03] Krypton

J. A. Cardelli (Villanova Univ.), D. M. Meyer (Northwestern Univ.)

From the chemical composition of Galactic interstellar dust to the metallicity of QSO absorption line systems, solar system (photospheric and/or meteoritic) elemental abundances have served as the standard against which such measures have been compared and interpreted. However, recent analysis of the interstellar abundance of oxygen (Meyer et al. 1994), particularly in low density sight lines, has suggested that solar abundances may not be generally representative of the true (average) cosmic abundance. Specifically, the ISM abundance measures of oxygen suggest that the solar system might be over abundant in O by as much as a factor 2. Similar results are also suggested from analyses of the Fe-peak element zinc (Roth \& Blades 1995; Sembach et al. 1995). However, a major difficulty in these analyses is that fact that both elements show some level of depletion onto dust grains which makes definitive interpretation difficult.

To avoid this potential pitfall, we have obtained interstellar abundance data of the chemically inert noble gas element krypton toward six stars in three distinct Galactic directions. Since krypton is not expected to deplete onto dust (Kr I is the dominant form in the ISM and so is characterized by a filled outer shell, 4$p^6$) its interstellar abundance should reflect the true cosmic abundance. For all six sight lines, which probe moderate to very low density gas, we find that the ISM abundance of krypton is constant and roughly a factor 2 below that inferred for the solar system. This result strongly supports the conclusions derived from the study of oxygen and zinc and suggests that elemental abundances in the solar system may be (generically?) too high by perhaps as much as a factor 2. These results are also generally consistent with elemental abundances (C, N, and O) observed in early B-type stars (Gies \& Lambert 1992).

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