Observations of Interstellar Argon with IMAPS

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Session 12 -- Interstellar medium
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[12.04] Observations of Interstellar Argon with IMAPS

U. J. Sofia (NASA/GSFC/NRC), E. B. Jenkins (Princeton Univ. Obs.), G. Sonneborn (NASA/GSFC)

Argon has a first ionization potential of 15.76 eV, therefore it exists as Ar {\sc i} in the neutral interstellar medium. Since it is a noble gas, Ar is unlikely to produce bonds which would deplete it onto dust grains. The same argument can be put forth for Kr, however recent measurements by Cardelli et al. show an apparent depletion of this element. Since their data indicate approximately the same level of depletion in each of their sight lines, one may infer that the cosmic abundance of Kr is in error. Data from Copernicus ($\sim$15 km s$^{-1}$ resolution) however suggest that Ar may also be depleted with respect to hydrogen in some neutral interstellar clouds. The location of the Ar {\sc i} resonance transition lines at $\lambda\lambda$1048 and 1066\AA \space has made confirmation of this finding difficult. Using data obtained with the Interstellar Medium Absorption Profile Spectrograph (IMAPS) which produces $\sim$2 km s$^{-1}$ resolution spectra in the 950 - 1150\AA\space wavelength region, we will determine interstellar argon abundances and depletion levels in the sight lines toward $\gamma^{2}$ Vel, $\zeta$ Pup and $\alpha$ Eri. The high-resolution of the IMAPS data will help to alleviate the problem of blended saturated lines which are often a large source of error in abundance determinations.

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