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Magnetic fields around BOK globules: CCD polarimetry of CB 4
The small Bok globule CB 4 was probed using a CCD imaging polarimeter inorder to create a detailed map of the magnetic field associated withthis cloud. Stars as faint as 17th mag at V band were measuredpolarimetrically with uncertainties less than 1%. Sky transmissionvariations were minimized via a system of synchronous polaroid rotationand bidirectional charge shifting. In all, 80 stars behind the peripheryof the globule were accurately analyzed polarimetrically. Thelarge-scale (1-2 pc) magnetic field direction around CB 4 was found tobe very uniform (P.A. = 63.3 deg +/- 1.1 deg). Double-Gaussian fittingof the polarization position angle histogram gave a dispersion of 10 degabout the primary field direction. Possible field-line compression wasfound inward of approximately 0.2 pc from the cloud center. Noappreciable twisting of field lines was found. By plotting stellarseparations against differences of polarization angles, CB 4 was foundto have a magnetic field decorrelation length of approximately 0.1 pc,similar to the size of the visually opaque cire, but much smaller thanthe size of the bright optical rim or CO half-power contour ofapproximately 0.5 pc. The magnetic field decorrelation length may berelated to a characteristic transient clumping size, or perhaps even toclumps of a more permanent nature.
| Four-colour and H beta photometry of southern B stars at high galactic latitudes
Four-color and H beta photometry has been obtained for 105 early-type HDstars with galactic latitudes less than -45 deg. They are mostly late Bstars of luminosity class V to III. Two new Am stars and several Ap orBp stars are detected photometrically. Absolute magnitudes aredetermined from the photometry and from MK types where available. Theinterstellar reddening of many of the more distant stars is very small,suggesting either the existence of undetected peculiar stars in thesample or that there are areas of effectively zero reddening at highsouthern galactic latitudes.
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