Observations and physical interpretations of coronal rays from white light, soft X-ray, red (FeX) and green (FeXIV) lines analyses

Abstract

The purpose of this investigation is to determine the physical and morphological characteristics of the coronal rays as seen in white light and compare these structures to rays seen in soft X-ray, FeX (red) and FeXIV (green) line emissions. During the quiescent phase in solar activity, coronal rays were observed in white light both in the polar and equatorial regions by Spartan 201 and Mark-III. White light coronal rays have a brightness contrast of 10–40% compared to the adjacent structures. Polar coronal rays were observed in the red line emission and part of the time rays were also observed in soft X-ray and green line emission. The intensity contrast of the rays and the adjacent structures in these lines are ≈20–100%, in agreement with the white light observations. Polar rays observed in red line emission are designated as ‘cool’ rays while those observed in soft X-ray and green line emission are called ‘hot’ rays. Cool rays are a dominant feature of the polar corona during the quiescent phase of the solar cycle. The hot rays when present form a small subset of the rays seen in white light which can be either ‘cool’ or ‘hot’. Hot rays seem to emerge from the boundary of the polar coronal hole (polar crown filament belt). The location of the cool rays on the other hand seems to remain an open question. The average half width of all the rays, in the plane of the sky, were found to be about 2–3° and did not change with height. This width is similar to that of the supergranular cells. The fact that the scale height temperature in the hole and rays shows a rise and reaches a peak as a function of height suggests that heat is being deposited in the corona extending from 1.4–2.6 R⊙.