Mapping Cool Gas in the ISM with ROSAT

Abstract We have investigated the distribution of cool gas within the local interstellar medium (<150 pc) using data derived from both the ROSAT X-ray and EUV all-sky surveys. The EUV/X-ray spectra for a sample of 89 white dwarf stars and 200 active late-type stars have been analysed to give an estimate of the gas column density along each object’s line of sight. In order to extend the sky coverage we have also included in the analysis 190 late-type stars detected only in the X-ray band. The derived NHI measurements confirm the size of the local low density bubble as typically 50-100 pc and also show that in the general direction of Loop I there is a substantial excess of absorption at a range of distances from 10-150 pc.