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Local Interstellar Matter: The Apex Cloud
Several nearby individual low column density interstellar cloudlets havebeen identified previously on the basis of kinematical features evidentin high-resolution Ca+ observations near the Sun. One ofthese cloudlets, the ``Apex Cloud'' (AC), is within 5 pc of the Sun inthe solar apex direction. The question of which interstellar cloud willconstitute the next Galactic environment of the Sun can, in principle,be determined from cloudlet velocities. The interstellar absorptionlines toward α Cen (the nearest star) are consistent withinmeasurement uncertainties with the projected ``G'' cloud (GC) and ACvelocities, and also with the velocity of the cloud inside of the solarsystem (the local interstellar cloud [LIC]), provided a small velocitygradient is present in the LIC. The high GC column density towardα Oph compared to α Aql suggests that α Aql may beembedded in the GC so that the AC would be closer to the Sun than theGC. This scenario favors the AC as the next cloud to be encountered bythe Sun, and the AC would have a supersonic velocity with respect to theLIC. The weak feature at the AC velocity toward 36 Oph suggests that theAC cloud is either patchy or does not extend to this direction.Alternatively, if the GC is the cloud that is foreground to α Cen,the similar values for N(H0) in the GC components towardα Cen and 36 Oph indicate this cloud is entirely contained withinthe nearest ~1.3 pc, and the Ca+ GC data toward α Ophwould then imply a cloud volume density of ~5 cm-3, withdramatic consequences for the heliosphere in the near future.
| CCD measurements of visual binaries
CCD measurements of visual double stars were obtained with the ESO 1.5 mdanish reflector. All binaries observed are candidates for the HIPPARCOSInput Catalogue. More than 400 observations have been made in four clearnights. The accuracy obtained is comparable to the accuracy of thephotographic technique, but the observing and reduction times are oneorder of magnitude smaller.
| A spectral survey of the southern Milky Way 1 : general description and catalogue 1 (l=306 -318 degrees).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...16..445S&db_key=AST
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