The long-term stability of the visible F corona at heights of 3-6 R_&sun;

Details The long-term stability of the visible F corona at heights of 3-6 R_&sun; The long-term stability of the visible F corona at heights of 3-6 R_&sun;

Aug 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007a%26a...471l..47m&link_type=abstract

Astronomy and Astrophysics, Volume 471, Issue 2, August IV 2007, pp.L47-L50

Astronomy and Astrophysics

Astrophysics

5

Sun: Corona, Interplanetary Medium, Sun: Activity

Scientific paper

Context: CMEs can effect the distribution of dust grains in the corona. The brightness of the visible F corona is expected therefore to change as the frequency of CMEs varies with solar cycle. Aims: We search for a variation in the F corona by comparing LASCO C2 observations from solar minimum and maximum. Methods: An established inversion method is used to calculate the visible F corona brightness from LASCO C2 solar minimum observations made during 1996/10. Good agreement is found with the F corona brightness calculated from Skylab observations during 1973/05-1974/02 for heights of 3-6 R_&sun;. The unpolarized brightness, which is dominated by the unpolarized F corona brightness at these heights, is obtained by subtracting many pairs of polarized brightness images from total brightness images and averaging over a solar rotation. We calculate the unpolarized brightness for both solar activity minimum and maximum. Results: The unpolarized brightness, and therefore the F corona, remain virtually unchanged between solar minimum and maximum at heights above 2.6 R_&sun;, despite the large change in the shape and activity of the corona. Using a simple density model, it is shown that the small variation in unpolarized brightness seen below 2.6 R_&sun; can arise from differences in the distribution of electron density, and therefore cannot be attributed to a variation in the F corona. Conclusions: Despite the large rise in frequency of CMEs from solar minimum to maximum, the F coronal brightness, at heights of 3-6 R_&sun; in the visible, remains very stable.

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