Abstract
We present medium-resolution spectra (R ∼ 7.5 km s −1 ) of the interstellar NaI and CaII interstellar absorption lines observed towards 16 early-type stars with distances of 160-1 kpc in the line-of-sight towards the Orion-Eridanus Superbubble (OE-S). These data have been supplemented with measurements of NaI absorption towards a further 13 stars with similar sight-lines taken from the literature. We detect two major absorption components with velocities of Vlsr ∼ +7.0 and −8.0 km s −1 . The former component, seen in 70% of the sight-lines is associated with the boundary to the Local Bubble cavity located at a distance of 140-150 pc. The other absorption component is only detected towards a limited region of the sky bounded by (190 ◦ 220 pc within an area coincident with that of the 0.75 keV X-ray enhancement of the OE-S. Column density ratios, N(NaI)/N(CaII), for the most negative velocity components have values 500 pc. Finally, we place a similar distance limit for any coherently structured rear shell of neutral gas associated with expansion of the OE-S towards the galactic halo.
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