X‐Ray Shadows by High‐latitude Molecular Clouds. I. Cartography

Abstract

We have observed X-ray shadowing by nine nearby high-latitude molecular clouds with the ROSAT PSPC. The $f {1}{4} $ --> keV emission from the Local Bubble is used to calculate an average electron density, ne, toward all of our sample clouds. Given the uniformity of emission within the Local Bubble, and previously determined cloud distances, one can determine whether the clouds are within or without the Local Bubble. We confirm that three of the sample clouds, MBM 12, MBM 16, and possibly MBM 20, which have been thought to be within the Local Bubble, are actually within. A combination of $f {1}{4} $ --> keV and ne measures suggest that MBM 6 and LDN 1563 may also lie within the Local Bubble or its boundary layer. The shadows cast by the clouds at $f {3}{4} $ --> keV and 1.5 keV imply little if any foreground emission in those bands, and produce lower limits for the distance to the hotter emission component responsible for the observed flux. The results are in agreement with previous estimates for the distances to the Loop I Bubble and the Eridion Bubble.