ANOMALOUS WIDENING OF 5434.5 LINE IN SUNSPOTS: SUPER-STRONG MAGNETIC FIELDS?

Анотація

We present results of spectral
observations of two sunspots in six metal lines near Fe I
5434.5 Å, which have effective Lande factors g eff from –
0.014 to 2.14. The observations were made on July 8 and
August 25, 2015, with the ATsU-5 telescope of GAO NAS
of Ukraine using a circular polarization analyzer and
spectra registration with the SBIG ST-8300 CCD camera.
The following line parameters are compared: observed
splitting of I ± V profiles, the width and depth of the Stokes
I profiles. Significant differences of the measured magnetic
field strengths B eff were found in separate places of the
spots and by lines with different g eff values. The Fe I 5434.5
Ǻ line (g eff = –0.014) shows measurable splitting in some
locations of the sunspots, which corresponds to the
magnetic field B obs ≈ 20 kG. Comparison of the widths and
depths of the line profiles revealed several special places in
the sunspots, where the Fe I 5434.5 Ǻ line was expanded
additionally by ≈ 15–35%, whereas other lines with larger
Lande factors did not have such a feature. One of the
reasons for this expansion could be a sharp and local
increase of turbulent velocities, but no active processes such
as solar flares or significant Doppler flows were observed at
these locations. A semi-empirical model constructed for the
first sunspot by FeI 5434.5 line using inverse code with
Tikhonov`s stabilizers shows an anomalous feature – the
maximum of microturbulent velocities in the upper
photosphere and the temperature minimum zone instead of
the usual small increase of microturbulence at these heights.
This may be the effect of very strong magnetic fields of
mixed polarity or unresolved turbulent structures. As to first
case, the estimated value of the magnetic field in such
locations of sunspots is ~10 5 G, which requires additional
careful verification.