1. Strong Photospheric Heating Indicated by Fe I 6173 {\AA} Line Emission During White-Light Solar Flares
- Author
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Granovsky, Samuel, Kosovichev, Alexander G., Sadykov, Viacheslav M., Kerr, Graham S., and Allred, Joel C.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
Between 2017 and 2024, the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory has observed several white-light solar flares. Notably, for the X9.3 flare of September 6, 2017, HMI spectro-polarimetric observations reveal one or more locations within the umbra of the associated active region where the Fe I 6173 {\AA} line goes into full emission, indicating significant heating of the photosphere and lower chromosphere. For these flares, we performed a spectro-polarimetric analysis at the aforementioned locations using HMI 90s cadence Stokes data. At the Fe I emission locations, line-core emission is observed to last for a single 90 s frame and is either concurrent with or followed by increases in the line continuum intensity lasting 90 to 180 seconds. This is followed by a smooth decay to pre-flare conditions over the next three to twenty minutes. For most locations, permanent changes to the Stokes Q, U, and/or V profiles were observed, indicating long-lasting non-transient changes to the photospheric magnetic field. These emissions coincided with local maxima in hard X-ray emission observed by the Konus instrument onboard the Wind spacecraft, as well as local maxima in the time derivative of soft X-ray emission observed by GOES satellites. Comparison of the Fe I 6173 {\AA} line profile synthesis for the ad-hoc heating of the initial empirical VAL-S umbra model and quiescent Sun (VAL-C-like) model indicates that the Fe I 6173 {\AA} line emission in the white-light flare kernels could be explained by the strong heating of initially cool photospheric regions.
- Published
- 2024