0559604 - ASÚ 2023 RIV GB eng J - Journal Article
Lörinčík, J. - Dudík, Jaroslav - Polito, V.
Blueshifted Si iv 1402.77 angstrom Line Profiles in a Moving Flare Kernel Observed by IRIS.
Astrophysical Journal. Roč. 934, č. 1 (2022), č. článku 80. ISSN 0004-637X. E-ISSN 1538-4357
R&D Projects: GA ČR GA20-07908S
Institutional support: RVO:67985815
Keywords : solar transition region * solar ultraviolet emission * solar flares
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 4.9, year: 2022
Method of publishing: Open access

We analyze the spectra of a slipping flare kernel observed during the 2015 June 22 M6.5-class flare by the Interface Region Imaging Spectrograph (IRIS). During the impulsive and peak phases of the flare, loops exhibiting an apparent slipping motion along the ribbons were observed in the 131 angstrom channel of SDO/AIA. The IRIS spectrograph slit observed a portion of the ribbons, including a moving kernel corresponding to a flare loop footpoint in Si iv, C ii, and Mg ii at a very-high 1 s cadence. The spectra observed in the kernel were mostly redshifted and exhibited pronounced red wings, as typically observed in large flares. However, in a small region in one of the ribbons, the Si iv 1402.77 angstrom line was partially blueshifted, with the corresponding Doppler velocity divide v (D) divide exceeding 50 km s(-1). In the same region, the C ii 1334.53, 1335.66, and 1335.71 angstrom lines were weakly blueshifted ( divide v (D) divide < 20 km s(-1)) and showed pronounced blue wings, which were also observed in the Mg ii k 2796.35 angstrom as well as the Mg ii triplet 2798.75 and 2798.82 angstrom lines. Using high-cadence AIA observations we found that the region where the blueshifts occurred corresponds to the accelerating kernel front as it moved through a weak field region. The IRIS observations with high resolution allowed us to capture the acceleration of the kernel under the slit for the first time. The unique observations of blueshifted chromospheric and TR lines provide new constraints for current models of flares.
Permanent Link: https://hdl.handle.net/11104/0333348