The Equatorial Background Solar Corona during Solar Minimum

Details The Equatorial Background Solar Corona during Solar Minimum The Equatorial Background Solar Corona during Solar Minimum

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...648..707r&link_type=abstract

The Astrophysical Journal, Volume 648, Issue 1, pp. 707-711.

Astronomy and Astrophysics

Astronomy

2

Scattering, Sun: Activity, Sun: Corona, Sun: Radio Radiation

Scientific paper

We report two-frequency (51 and 77 MHz) radio observations of the equatorial brightness distribution of the ``undisturbed'' solar corona, close to the minimum between sunspot cycles 22 and 23. The contributions from different discrete structures in the observed one-dimensional profiles were identified and removed through an iterative multi-Gaussian least-squares curve fitting technique, and the ``background'' corona was obtained for each observation. Its average east-west (E-W) diameter is 43'+/-4' and 38'+/-2' at 51 and 77 MHz respectively. This indicates that the plasma levels corresponding to the above two frequencies are located at radial distances (r, measured from center of the Sun) of ~1.35 and 1.19 Rsolar and the electron density (Ne) there is 3.2 and 7.3×107 cm-3, respectively. Using the above values, we derived the corresponding density gradient, ~r-6.5. We also calculated the integrated flux densities (S) of emission from the background corona; the average values are ~0.46 and 1.12 sfu (1 sfu = solar flux unit = 10-22 W m-2 Hz-1) at the above two frequencies. The corresponding brightness temperatures (Tb) are 3.85 and 5.44×105 K. We estimated the spectral dependence of the former, finding that it scales as ν2.2, where ν is the frequency of observation. The day-to-day values of the E-W diameter show significant variation at both 51 and 77 MHz, even after the removal of contributions from discrete sources.

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