We report the detection of atomic chlorine emissions in the atmosphere of Io using Hubble Space Telescope observations with the Goddard High Resolution Spectrograph (GHRS). The Cl I 1349 A dipole allowed and Cl I] 1386 A forbidden transition multiplets are detected at a signal to noise ratio (SNR) of 6 and 10, respectively, in a combined GHRS spectrum acquired from 1994 through 1996. Oxygen and sulfur emissions are simultaneously detected with the chlorine which allows for self-consistent abundance ratios of chlorine to these other atmospheric species. The disk averaged ratios are: Cl/O = 0.017 +/- 0.008, Cl/S = 0.10 +/- 0.05, and S/O = 0.18 +/- 0.08. We also derive a geometric albedo of 1.0 +/- 0.4 % for Io at 1335 A assuming an SO2 atmospheric column density of 1x10^{16} cm^{-2}.
@article{arxiv.astro-ph/0404508,
title = {Detection of Atomic Chlorine in Io's Atmosphere with HST/GHRS},
author = {Lori M. Feaga and Melissa A. McGrath and Paul D. Feldman and Darrell F. Strobel},
journal= {arXiv preprint arXiv:astro-ph/0404508},
year = {2009}
}
Comments
23 pages, 5 figures, accepted for publication in ApJ, August 1, 2004