ON THE POSSIBLE EXISTENCE OF SUPERSTRONG MAGNETIC FIELDS IN A LIMB SOLAR FLARE

Анотація

We present the simultaneous
observations of the K Ca II 3933.7 Å, H δ 4101.7 Å and
He I 4471.5 Å lines in the limb solar flare of July 17,
1981. For two moments of the flare we analyzed Stokes
I ± V and V profiles of these lines from observations
made on the Echelle spectrograph of the horizontal solar
telescope of the Astronomical Observatory of Taras
Shevchenko National University of Kiev. In the flash
phase of the flare, all named lines had very wide
emissions, with a wing length of 6–8 Å. An interesting
feature was observed in the violet wings of these lines,
namely, narrow emission peaks with a width of only 0.25–
0.35 Å. The Zeeman splitting of these emission peaks
correspond to magnetic field strength in range 1300-2900
G at altitudes of 10–15 Mm above the level of the
photosphere. Magnetic fields of ‘kilogauss’ range (up to
3200 G) were found for some locations also in post-peak
phase of the flare. Likely, the true local magnetic fields in
the flare could be even larger, since the obtained results
represent a longitudinal component of the magnetic field
assuming that the filling factor equals unity. A new
indication of the existence of superstrong magnetic fields
follows from a comparison of the kinetic temperatures and
turbulent velocities found from the narrow emission
component in the flash phase of the flare. Considering this
emission component to be optically thin, we found that
there is an anti-correlation between temperature and
turbulent velocity. Such a dependence seems unlikely and,
possibly, the widths of the line profiles reflect, in our case,
not turbulent velocities, but very strong magnetic fields.
The corresponding estimates of the magnetic field by the
K Ca II line lead to the value B = 8.3 kG, and by the He I
4471.5 line - to the value B = 6.7 kG. Considering that the
He I line is clearly closer to the case of an optically thin
layer, the closeness of these estimates is very encouraging.
Our results are apparently the first indications of
superstrong magnetic fields of 6-7 kG at an altitude of
about 10 Mm in a solar flare