Spectral Characteristics and Formation Height of Off-limb Flare Ribbons

0534353 - ASÚ 2021 RIV US eng J - Journal Article
Kuridze, D. - Mathioudakis, M. - Heinzel, Petr - Koza, J. - Morgan, H. - Oliver, R. - Kowalski, A.F. - Allred, J.C.
Spectral Characteristics and Formation Height of Off-limb Flare Ribbons.
Astrophysical Journal. Roč. 896, č. 2 (2020), č. článku 120. ISSN 0004-637X. E-ISSN 1538-4357
R&D Projects: GA ČR(CZ) GA19-09489S
Institutional support: RVO:67985815
Keywords : white-light flare * h-alpha * nonthermal electrons
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 5.877, year: 2020
Method of publishing: Open access

Flare ribbons are bright manifestations of flare energy dissipation in the lower solar atmosphere. For the first time, we report on high-resolution imaging spectroscopy observations of flare ribbons situated off limb in the H beta and Caii 8542 A lines and make a detailed comparison with radiative hydrodynamic simulations. Observations of the X8.2 class solar flare SOL 2017-09-10T16:06 UT obtained with the Swedish Solar Telescope reveal bright horizontal emission layers in H beta line-wing images located near the footpoints of the flare loops. The apparent separation between the ribbon observed in the H beta wing and the nominal photospheric limb is about 300-500 km. The Caii 8542 A line-wing images show much fainter ribbon emissions located right on the edge of the limb, without clear separation from the limb. RADYN models are used to investigate synthetic spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. The simulations show that, toward the limb, where the line of sight is substantially oblique with respect to the vertical direction, the flaring atmosphere model reproduces the high contrast of the off-limb H beta ribbons and their significant elevation above the photosphere. The ribbons in the Caii 8542 A line-wing images are located deeper in the lower solar atmosphere with a lower contrast. A comparison of the height deposition of electron beam energy and the intensity contribution function shows that the H beta line-wing intensities can be a useful tracer of flare energy deposition in the lower solar atmosphere.
Permanent Link: http://hdl.handle.net/11104/0313047