The nearby interstellar material in the general direction towards M22

Abstract

The globular cluster M22 |$(l\approx10^\circ; \enspace b\approx-8^\circ)$| lies well beyond an extensive region of gas and dust which is associated with the nearby H I cloud first mapped by Reigel & Crutcher. The gas foreground to the cluster at distance |$\approx 2.6$| kpc is essentially concentrated in two features at the approximate velocities (LSR) of + 6 and + 40 km s−1. High-resolution optical spectra of interstellar absorption lines are used to examine reddening variations across the cluster which are produced by the nearby, low-velocity material. Although equivalent width variations are detected on subparsec spatial scales the column densities which are derived from these data only provide some possible evidence for variability in the foreground gas column and reddening on such scales. Optical and ultraviolet spectra of closer stars which lie within several degrees of M22 confirm that a rapid increase in gas column density occurs at a distance of approximately 100 pc but the material is considerably more extensive in thickness than has been suggested previously. Although the current schematic models for the Loop I and local bubbles describe in a general way some of the observed features of this local interstellar material, they cannot account directly for the properties and thickness of the gas determined from this investigation.