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A search for SH(+) and CH(+) in diffuse and translucent clouds
Results are reported from a search for SH(+) absorption at about 336 nmfrom diffuse interstellar clouds and high-latitude molecular clouds inthe direction of nine early-type stars. Two of the lines of sight in thedirection of translucent high-latitude molecular clouds were alsosearched for CH(+) absorption at 4232 nm. Both CH(+) and SH(+) arebelieved to be formed by endothermic reactions which require the passageof a shock through the diffuse cloud. SH(+), in particular, is thoughtto form as a consequence of an MHD shock. SH(+) was not detected fromany of the lines of sight, nor was CH(+) detected from either of thehigh-latitude clouds. The N(SH+) upper limits obtained are marginallyinconsistent with the presence of MHD shocks with velocities greaterthan 14 km/s, and the nondetections of CH(+) for the high-latitudeclouds are inconsistent with current shock-chemistry models.
| On the nearest molecular clouds. II - MBM 12 and 16
The paper presents echelle spectra recorded at the D lines of Na I forthree stars projected on the high-latitude molecular cloud MBM 16 at l =172 deg, b = -38 deg. The A stars HD 21142 at about 95 pc and HD 21134at about 240 pc show strong D-line absorption at the same velocities asthe CO emission observed at these positions. The distance to MBM 16therefore is in the range of 60 to 95 pc. MBM 16 is only 11 deg awayfrom MBM 12, previously placed by the same method at distance of about65 pc. Consideration is given to the relationship between clouds 12 and16 and the local hot low-density interstellar gas.
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