view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Some polarization measurements in the Pleiades and Orion regions. Hall, John S. Abstract The light from 23 stars in the Plejades cluster has been examined photoelectrically for polarization with the Ritchey- Chretien reflector. One star in this group, HD 23512, is an 8.3 magnitude Ao star with large color excess which Binnendijk had cited as a star of special interest. Binnendijk's results1 and Eggen's data2 indicate that some of the other stars chosen for observation are space reddened. Measures of HD 23512 made on three nights indicate a polarization of 2.2 per cent and a plane of polarization at 1220.1 This angle is similar to those found, for other nearby stars in the Taurus region. None of the other Pleiades stars show positive evidence of polarization, despite the fact that some are within a few minutes of arc of the highly reddened star. Both the radial velocity and proper motion of this star indicate that it is a member of the cluster. P. W. Merrill was kind enough to examine a low-dispersion spectrogram of it, secured in the photographic region, and found it to be a rather ordinary main-sequence A-type star. Its distance of about a hundred parsecs makes it the nearest star known to exhibit polarization. Markowitz has secured a number of photographs of this region through calcite. His polarization measurements, which are still in progress, include stars of the 15th visual magnitude. An attempt to measure polarization in the light of the members of the Trapezium in the spring of 1949 revealed that the Orion nebula (NGC 1976) is polarized. A micrometer, later attached to the guiding telescope of the ~o-inch, made it possible to explore this nebula in some detail. The area of the sky admitted to the cathode of the pliotomultiplier at any one time Was 380 square seconds of arc. Preliminary measures made on three nights show that the plane of polarization consistently points toward the Trapezium as the source of light. The area so far observed which shows most polarization is 2' due west of HD 37022, where the value is slightly less than 4 per cent. Since the Trapezium stars show little or no polarization it seems probable that the polarization of the reflected or scattered light is not substantially modified as it comes through the nearer regions of the nebula. The reddened,B8 star, HD 37061, just north of the Orion nebula is polarized 1.6 per cent at 1530. This star is imbedded in bright nebulosity. Polarization measurements in the Orion region are to be continued and an attempt will be made to make them in different spectral regions. I.Ann. Stw. Leiden `9, Part II, 1946. 2.Ap. J. iii, 8i, 1950. 3.Pub. U. S. Naval Obs. 17, Part II, 1950. U. S. Naval Observatory, Washington, D. C. Publication: The Astronomical Journal Pub Date: April 1951 DOI: 10.1086/106491 Bibcode: 1951AJ.....56...40H full text sources ADS | data products SIMBAD (4)