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An investigation of grain properties in the Rho Ophiuchi dark cloud
A polarimetric, photometric, and spectroscopic survey of 134 stars inthe direction of the Rho Ophiuchi dark cloud, to an absorption depth ofAv less than 5-7 mag is presented. The extinction and polarization for19 stars foreground to the Rho Oph cloud are trivial compared to thoseobserved through the cloud itself. The ratio of total-to-selectiveextinction, R, determined from the color difference method, is found toincrease to R of about 4.1 at Av = 5.0 mag. Grain size, inferred fromlambda max, increases with optical depth in a manner that is consistentwith a simple model of coagulative grain growth. A high degree of grainalignment under a variety of ISM conditions is indicated. It issuggested that grain growth in Rho Oph is due to coagulation rather thanmantle accretion.
| On the Distance of the Scorpio / Centaurus Dark Cloud
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| Magnetic field structure in the vicinity of five dark cloud complexes
The magnetic-field geometry in the outer regions of five dark cloudcomplexes has been mapped by measuring the linear polarization of starsbackground to the cloud peripheries. These observations are aimed atestablishing a relationship between field geometry and cloud morphologyfor cloud complexes which are active sites of star formation. For one ofthese complexes, Barnard 42, polarization measurements were alsoobtained (at a wavelength of 2.2 microns) for several heavily obscuredstars in order to probe the magnetic-field geometry and grain-alignmentefficiency in the dense central regions of this dark cloud.
| New H-alpha emission stars in a region to the east of the T-Association near rho Ophiuchi.
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