A photoelectric photometer designed for measuring polarization, color, magnitude and spectral type.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A photoelectric photometer designed for measuring polarization, color, magnitude and spectral type. Hall, John S. Abstract As the light is transmitted through a cylinder of calcite it is split into two beams. The foci of the two beams are near two limiting apertures which rotate with the calcite at 15 cycles per second. The axial beam, or ordinary ray, passes through a hole in the center of a mirror and continues along the optical axis, to a photomultiplier. The alternating current which results if the starlight is polarized is presented as a sine wave on an automatic recorder once every two minutes.1 The off-axis beam, or extraordinary ray, is reflected from the mirror and made to pass through one of a sequence of four interference filters to a second photomultiplier. The direct current from this multiplier is amplified and displayed by a second recorder. A deflection, lasting about twenty seconds, for each color filter occurs once every two minutes. Preliminary reduction of the observations of 50 stars indicates that the polarization, magnitude and color of stars of the 10th magnitude and brighter can be accurately measured in this way with the ~o-inch telescope. The work of Stro~mgren2 has shown that observations with a narrow filter centered at H~ can be compared with those centered in adjacent spectral regions to determine spectral types. Suitable filters for accurate spectral classification have not yet been obtained here. A second direct-current amplifier and associated recorder is used for calibration purposes and to record possible changes in observed light intensity as the other measures are being made. This amplifier measures the average directcurrent level of the alternating current produced by the first photomultiplier. Polarized sky background can be automatically eliminated. Care must be exercised to make sure that there are no field stars close to the object under observation. With this photometer a new series of measurements of the Pleiades has been initiated. A year ago a polarization of 2.2 per cent was reported3 for the cluster member Hertzsprung 371. Recent measures have shown that another cluster member, Hertzsprung 322, shows equally strong polarization. A 470 difference in observed position angle exceeds the probable error of measurement b~ a factor of 15. The distance between these two cluster stars is probably less than two parsecs; if they are at equal distance from the sun, they are only 1/3 parsec apart. Several other cluster members are now suspected of showing polarization of 0.2 or 0.3 per cent. These observations suggest that this polarization is produced by clouds which are very small and possibl~ independent. I.Pub. U. S. Naval Obs. `7, Part I, 1950. 2.Trans. I. A. U. 7, 404, 1950. 3. A. J. ~6, 40, 1951. U. S. Naval Obseroatory, Washington, D. C. Publication: The Astronomical Journal Pub Date: April 1952 DOI: 10.1086/106772 Bibcode: 1952AJ.....57Q..12H full text sources ADS |