Wavelength Dependence of Solar Granulation- A Preliminary Report.
Abstract
A photoelectric study of the continuum brightness fluctuations in the solar granulation is being undertaken. The spectral range covers the interval 0.4 to 5 microns, and 10 microns with reduced accuracy. Maps, 16X32 sec of arc, made with an exploring hole of 0.5 sec of arc, require two minutes of time. Two such maps are made simultaneously for the same area, one in the visible with a photomultiplier, one in the infrared using a helium-cooled germanium bolometer. The process is then repeated at other pairs of wavelengths. Isobrightness contour maps are plotted by computer. The range of optical depths covered goes from 75000=1.58 (N=1.7~) to r~~~~=1.20 (N=0.4~) or 75000=0.12 (N 10~). Thus, the vertical scale involved is of the order of 125 km. Three-dimensional time-varying pictures of granulation are then provided. Fine structures, of the order of 1 sec of arc, have been observed at both 1.7 and 5 microns, correlating with the structures observed in the visible region. The rms value of the observed contrast between bright and dark areas varies from 4% (at 1.7~) to 1.2% (at 5~). The contrast observed is strongly affected by atmospheric seeing. Theory predicts that improved atmospheric seeing should be found at longer wavelengths, although the quantitative aspect of this wavelength dependence is not yet very clear. Measurements have been made in this study to evaluate the smearing of the solar limb by the atmospheric turbulence as a function of wavelength. Narrower smearing functions are found at longer wavelength, with a 1/NP dependence, where -13~p~-21. Despite the fact that the granular contrast on the sun decreases with increasing wavelengths, ground observations in the infrared may provide a picture of the granulation which would be closer to the actual contrast than is found from visible pictures.
- Publication:
-
The Astronomical Journal Supplement
- Pub Date:
- 1968
- Bibcode:
- 1968AJS....73R..67L