Session 7 - Gas and Dust in the ISM.
Display session, Monday, June 10
Great Hall,

## [7.11] The Abundance and Depletion of Interstellar Argon

U. J. Sofia (Villanova University), E. B. Jenkins (Princeton Univ. Obs.)

Observations of nine stars obtained with the Interstellar Medium Absorption Profile Spectrograph (IMAPS) have been used to determine the gas-phase abundance and depletion level of neutral interstellar argon. A direct ratio of the total interstellar Ar to H abundances toward \zeta Pup and \gamma^2 Vel indicate that argon is depleted in these two sightlines. The total Ar and/or total H interstellar abundances are not available for the seven remaining sightlines, \gamma Cas, \alpha Eri, \epsilon Ori, \zeta Ori, \kappa Ori, \beta Cru and \beta Cen. We therefore compare their interstellar Ar to interstellar N column densities as a function of velocity. Nitrogen shows little to no depletion in the interstellar medium, so the comparison of the two species can be used to identify Ar depletion. These results support the idea that Ar is depleted from the gas-phase ISM as compared to cosmic reference abundances. We will discuss explanations for the observed depletion of this neutral inert element.