Photoelectric observations of the electron solar corona.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoelectric observations of the electron solar corona. Wlerick, Gerard ; Axtell, James ; Lee, Robert Abstract The High Altitude Observatory staff has recently installed in Boulder a new instrument designed for the detection without eclipse of the electron solar corona. This component of the corona, often called the K-corona, is strongly polarized, the direction of the polarization being practically radial. It was successfully detected without eclipse in 1930 by B. Lyot at Pic du Midi with a coronagraph and a visual polarimeter able to detect a percentage of polarization as low as 0.1 per cent. Lyot's observations went as far as 0.35 R0 from the limb. The new instrument, called the K-coronameter, has been designed to permit observations at a greater distance from the edge of the sun, of the order of 0.5 to i.o R0. It is a coronagraph supplemented by a sensitive photoelectric polarimeter. The analyzer of polarization consists essentially of an electrically birefringent crystal excited by an a.c. voltage, a polarizer and a Lallemand photomultiplier. The a.c. signal from the multiplier is fed to a narrow band amplifier with synchronous detection. The band width is of the order of a few cycles per second. To reduce as much as possible the instrumental polarization, the coronal observations are always made on the axis. Thus, when scanning around the limb, the axis of the instrument describes a cone. A complete scan, at one given distance from the limb, takes 4 minutes. During the scan, a half-wave plate rotating at the speed of I round/ 8 min. keeps the plane of polarization of the light entering the analyzer in a fixed direction. With a relatively clear sky, Brightness B5 i~-~ B0, it has been possible in Boulder to detect the main features of the corona streamers up to 0.5 R0 and in one case up to o.66 R0. There is generally a good correlation between the brightness of the green coronal emission line measured with a conventional coronograph. It is planned to move the instrument to Climax this summer, at elevation I I 000 feet where better sky conditions prevail, and to make routine observations on clear days during the International Geophysical Year. The principal development work on this instrument was supported by the U. S. National Committee for the I.G.Y. under a grant from the National Science Foundation; a portion was supported by Radio Corporation of America. High Altitude Observatory, Boulder, Colo. Publication: The Astronomical Journal Pub Date: 1957 DOI: 10.1086/107631 Bibcode: 1957AJ.....62R..39W full text sources ADS |