Circular Polarimetry of Fifteen Interesting Objects

Abstract

A search is desci ibed for circular polarization of visible light in 15 objects: two eclipsing binaries (P Lyr and EM Ori); six magnetic Ap stars; three planetary nebulae; NGC 2261 (Rubble's Nebula); M87; Sirius; and the Orion A region. Broadly speaking, the results were null, down to typical upper limits for q of 0.01 percent. Maiginal but probably real resufts were obtained for IC 2022, q = +(0.070 I 0.025) percent, presumably due to the central star; and for a region in the Ori A region, wherein q = (0.060 t 0.025) percent in the red. Of the Ap stars only RD 126515 and RD 215441 appear to warrant more work at the photon-collection rate of the 88-inch telescope; in the others, topper limits for broad-band circular polarization of 0.01 percent or less are reported. The paper also contains a complete description of the photoelastic polarimeter, with special attention to the incidental linear-circular conversion.