Volume 471, Number 2, August IV 2007
|Page(s)||L47 - L50|
|Published online||09 July 2007|
Letter to the Editor
The long-term stability of the visible F corona at heights of 3–6 R\odot
Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA e-mail: email@example.com
Accepted: 3 July 2007
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 . 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 , 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 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 in the visible, remains very stable.
Key words: Sun: corona / interplanetary medium / Sun: activity
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.