H 2 S 3(1) and S 4(1) transitions in the atmospheres of Neptune and Uranus: Observations and analysis

Abstract

Observations of the S 3(1) and S 4(1) H 2 lines for Neptune are reported. The S 3(1) H 2 line yielded a measured equivalent width of 57 ± 6 m A ̊ , slightly one-half of the 107 ± 10 m A ̊ found for the same feature in Uranus. Both planets' H 2S 4(1) features were found to have equal equivalent widths to within the S/N, as also found previously. The equivalent width measurements for the S 3(1) and the S 4(1) H 2 lines in the atmospheres of Neptune and Uranus were obtained with the same instrumental configuration on the same nights. The observed ratio of the H 2S 3(0)/S 3(1) lines for Neptune's atmosphere is reproduced by members of the family of models derived by K. H. Baines and W. H. Smith (1990, Icarus 85, 65–108). Compared with the Uranus models of K. H. Baines and J. T. Bergstralh (1986, Icarus 65, 406–441) greater continuum absorption, produced largely by a deeper and/or darker tropospheric reflecting layer in Neptune, is responsible for the increased Neptune S 3(0)/S 3(1) line ratio near 0.82 μm.