Helioseismology from the South Pole: comparison of 1987 and 1981 results.
Abstract
Full disk images with ≡10 arc sec pixels and filtered to a ≡7 Å passband centered on the Ca II K line were obtained from the geographic South Pole in 1981 and 1987. In 1981, about 50 hours of essentially uninterrupted data were obtained. In 1987, three such runs were obtained over a period of 325 hours for a duty cycle of about 47%. The 1987 observations are characterized by a much lower level of solar activity than 1981, a much improved CCD camera, considerably better image stability and a varying amount of instrumental scatter. The 1987 data have a substantially better signal-to-noise ratio than the 1981 data so that oscillations with degrees from 0 to 150 and frequencies from 2 to 7 mHz are well observed. The observations were reduced to spectra in l, m and ν. This paper presents a comparison of p-mode frequencies measured in 1981 and 1987 and coefficients of Legendre polynomial expansions of frequency shifts caused by solar rotation. The authors also study the time behavior of systematic frequency shifts which depend upon m but which do not arise from rotation.
- Publication:
-
Seismology of the Sun and Sun-Like Stars
- Pub Date:
- December 1988
- Bibcode:
- 1988ESASP.286..279J
- Keywords:
-
- Helioseismology;
- Solar Interior;
- Solar Oscillations;
- Sun;
- Annual Variations;
- Ground Stations;
- P Waves;
- Solar Activity;
- Solar Rotation;
- Solar Physics;
- Sun: Seismicity;
- Solar Oscillations: Astronomical Instruments;
- Solar Oscillations: Solar Patrol