An ultra-high-resolution study of the interstellar medium in the direction of α Ophiuchi

I present very high resolution (R = 400 000 and R = 880 000) observations of interstellar Ca ii absorption lines towards eight early-type stars situated within 15 degrees of alpha Oph on the sky. I confirm an earlier result that the interstellar structure responsible for the anomalously strong Ca ii absorption towards a Oph has a spatial extent of less than or similar to1 pc (and is probably very much smaller). Many discrete interstellar absorption components are apparent in these high-resolution data, but while several have velocities in the range expected for the local interstellar medium (LISM), no convincing detections of either the local interstellar cloud (LIC), or the so-called G cloud, were made. In the former case, I argue that the relatively weak LIC components are masked by components arising in more distant clouds, but which have LISM-like velocities owing to the pervasive influence of outflow from the Sco-Cen association. The non-detection of the G cloud is more problematical, and I tentatively argue that, previous claims notwithstanding, this feature does not extend to galactic latitudes as high as + 15 degrees in this direction.