Study of the red coronal line with altitude from out-of-eclipse observations during solar cycle 24

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Abstract

The article presents the results of studies of the emission coronal line λ = 6374 Å (FeX) for the period of solar cycle 24. The spectral data were obtained with an out-of-eclipse Lyot coronagraph at the Mountain Astronomical Station of the Pulkovo Observatory, Russian Academy of Sciences (near Kislovodsk). Based on the processing of the results of out-of-eclipse observations, a database of three types of daily coronal maps with a distribution by altitude h from 1 Rʘ to 1.38 Rʘ (Rʘ is the radius of the Sun) of the red line intensity (I6374) was created. Throughout the solar cycle, spectral observations demonstrating a Doppler shift along the red line λ = 6374 Å were found. The extension of the red line from the limb position angle of the Sun was calculated. It was shown that the maximum value of the average extension of the coronal line over the entire limb falls on the ascent branch of solar cycle 24. For different phases of the considered solar cycle (for the ascending branch, the period of maximum, the descending branch and the minimum of solar activity) and for different regions of solar activity, the dependences of the change in I6374 values with altitude were plotted and explained. A regression analysis of the obtained relationships is carried out. The regression equations are presented. The changes in I6374 with altitude for the polar regions (for all phases of the cycle except for the maximum and the descending branch) and for the middle latitudes (for the minimum of activity) most likely have a logarithmic dependence, and the approximating trend curves for the remaining latitudinal zones are determined by a third-order power function.

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About the authors

S. A. Guseva

Kislovodsk Mountain Astronomical Station of Central (Pulkovo) Astronomical Observatory, Russian Academy of Sciences

Author for correspondence.
Email: svgual@yandex.ru
Russian Federation, Kislovodsk

A. D. Shramko

Kislovodsk Mountain Astronomical Station of Central (Pulkovo) Astronomical Observatory, Russian Academy of Sciences

Email: а_shramko@inbox.ru
Russian Federation, Kislovodsk

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Supplementary files

Supplementary Files
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2. Fig. 1. Change in the intensity of the coronal line λ = 6374 Å (FeX) during the 24th SA cycle. The thin line shows the daily values of I6374 (abs. units) averaged over the entire limb, and the thick line shows their monthly average values

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3. Fig. 2. Panel (a) – examples of the inhomogeneous coronal line λ = 6374 Å during the emission of an eruptive prominence of the “surge” type in the Hα line (λ = 6563 Å) and in the emission line of the Mg triplet (λ = 5167 Å, λ = 5173 Å, λ = 5184 Å). The date and position angle are indicated; Panel (b) – an example of a spectrum with emission in the coronal line λ = 6374 Å, Hα (λ = 6563 Å) and Ba (λ = 6497 Å), where 125° is the position angle; Panel (c) – examples of irregularities along the coronal line λ = 6374 Å above active regions near the limb

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4. Fig. 3. Examples of daily coronal maps of the spectral corona with I6374 at an altitude of h (1–1.32) Rʘ: (a) – maps with plotted isolines of I6374 values at different altitudes from the solar limb; (b) – maps displaying the distribution of I6374 values with altitude, as a gray scale (in inversion); (c) – 3D maps of the I6374 spectral corona at a certain altitude, where h = 40”

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5. Fig. 4. Graphs showing the dynamics of the extension of the coronal line λ = 6374 Å (FeX) for the 24th solar activity cycle: (a) – changes in the values of the maximum hmax and average hсp extension of the line over the entire limb; (b) – variations in the average hсp extension of the line over certain latitudinal zones of solar activity: 1 – equatorial; 2 – average; 3 – polar

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6. Fig. 5. Change in the intensity of the λ 6374Å line with altitude h for the 24th solar activity cycle: (a) – dependence of I6374 for different latitudinal zones of the solar limb: 1 – equatorial; 2 – average; 3 – polar; 4 – the entire solar limb; (b) – distribution of I6374 separately for the ascent branch (↗) and decline (↘), maximum (max) and minimum (min) phases of the SA cycle, where the numbers indicate the latitudinal zone

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