Abstract
X-ray photographs obtained with a zone plate camera on October 3, 1967 in the wavelength band 49.5–52.5 Å have been investigated photometrically.
The most intense X-ray emission corresponds with active regions in Hα and Ca ii. About one quarter of the total solar flux is emitted by the three brightest X-ray sources (A, E and J). X-ray emission from quiet regions is also observed. Limb brightening is found, also at the poles, which indicates a higher electron density at the poles than during solar minimum.
The brightest X-ray regions have a very small core of the order of 20″. No relation to magnetic field strengths of sunspots has been found. However, a correlation with active prominences cannot be ruled out. X-ray source A is related either to prominence activity or to flare activity. One X-ray region (J) is probably related to flare activity.
Assuming an electron temperature of 3 × 106K to 5 × 106K for coronal active regions an emission measure of a few times 1049 cm−3 is derived, which yields an electron density of a few times 1010 cm−3.
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Burger, M., Dijkstra, J.H. Photographs of the Sun in the XUV-region. Sol Phys 24, 395–404 (1972). https://doi.org/10.1007/BF00153381
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DOI: https://doi.org/10.1007/BF00153381