IUE observations of high velocity interstellar gas tentatively associated with Radio Loop II.

Abstract

Red-shifted high velocity gas components (HVC) have been positively detected in IUE spectra of six out of a sample of eleven selected stars across a region of sky of some 40°. Properties of the HVC determined from the spectra of three stars indicate that the material is cool gas with a density n_H ≈ 100 cm^-3 and thickness ≈0.1 pc. The HVC velocities are consistent with a large expanding spherical shell of gas having the parameters of Radio Loop II, in which case the expansion velocity deduced for the shell is ≈100 km s^-1. Whilst the authors tentatively associate the HVC with Loop II the IUE observations suggest also that they may be smaller scale features which are connected with the larger loop.