Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.2201p&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #22.01; Bulletin of the American Astronomical Society, Vol. 24, p.1156
Other
Scientific paper
We present results from a comprehensive observational study of the high galactic latitude molecular clouds. Using photometric observations of over 320 stars, we charactarize the distance and extinction toward 25 high galactic latitude cloud regions. Methods of photometric stellar classification using both the UBV,Hβ and the uvby,Hβ systems are refined and applied to the high galactic latitude clouds. A new technique of automated digital spectral classification is also developed, and MK spectral types are assigned for 115 stars. The work provides distance estimates for MBM3, MBM 15, MBM 41, and several other high latitude clouds, and identifies many reddened stars toward high latitude clouds. In the second part of the work, high resolution spectra (delta lambda /lambda > 50,000) are used to examine the velocity and kinematics of several high galactic latitude complexes, and to further constrain the distances of the clouds. We present high resolution Na I D spectra for over 90 stars, and detections of optical absorption in the molecular species CH, CH(+) , for 17 sightlines. The optical absorption lines are used to derive physical conditions in the clouds, by using ionic ratios of N(Ca I)/N(Ca II) and N(Na I)/N(H I) to estimate the cloud densities, and N(CH)/N(CH(+) ) to compare the HLC's with molecular models. The high galactic latitude clouds are found to be very dense and compact, with densities of n{_H} > 1,000 cm(-2) and sizes of r < 0.1 pc in many cases. The high galactic latitude clouds appear to offer an ideal laboratory for studying the conditions in the molecular phase of the galaxy, and offer the opportunity for many further advances in understanding the structure and composition of molecular clouds.
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