Spectral lines formed at lower atmospheric layers show peculiar profiles at the “leading edge” of ribbons during solar flares. In particular, increased absorption of the BBSO/GST He
- NSF-PAR ID:
- 10320726
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 924
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract While solar flares are predominantly characterized by an intense broadband enhancement to the solar radiative output, certain spectral lines and continua will, in theory, exhibit flare-induced dimmings. Observations of transitions of orthohelium He i λ λ 10830 Å and the He i D3 lines have shown evidence of such dimming, usually followed by enhanced emission. It has been suggested that nonthermal collisional ionization of helium by an electron beam, followed by recombinations to orthohelium, is responsible for overpopulating those levels, leading to stronger absorption. However, it has not been possible observationally to preclude the possibility of overpopulating orthohelium via enhanced photoionization of He i by EUV irradiance from the flaring corona followed by recombinations. Here we present radiation hydrodynamics simulations of nonthermal electron-beam-driven flares where (1) both nonthermal collisional ionization of helium and coronal irradiance are included, and (2) only coronal irradiance is included. A grid of simulations covering a range of total energies deposited by the electron beam and a range of nonthermal electron-beam low-energy cutoff values were simulated. In order to obtain flare-induced dimming of the He i 10830 Å line, it was necessary for nonthermal collisional ionization to be present. The effect was more prominent in flares with larger low-energy cutoff values and longer lived in weaker flares and flares with a more gradual energy deposition timescale. These results demonstrate the usefulness of orthohelium line emission as a diagnostic of flare energy transport.more » « less
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Abstract In this paper, we report the observed temporal correlation between extreme-ultraviolet (EUV) emission and magneto-acoustic oscillations in an EUV moss region, which is the footpoint region only connected by magnetic loops with million-degree plasma. The result is obtained from a detailed multi-wavelength data analysis of the region with the purpose of resolving fine-scale mass and energy flows that come from the photosphere, pass through the chromosphere and finally heat the solar transition region or the corona. The data set covers three atmospheric levels on the Sun, consisting of high-resolution broad-band imaging at TiO 7057 Å and the line of sight magnetograms for the photosphere, high-resolution narrow-band images at helium i 10830 Å for the chromosphere and EUV images at 171 Å for the corona. The 10830 Å narrow-band images and the TiO 7057 Å broad-band images are from a much earlier observation on 2012 July 22 with the 1.6 meter aperture Goode Solar Telescope (GST) at Big Bear Solar Observatory (BBSO) and the EUV 171 Å images and the magnetograms are from observations made by Atmospheric Imaging Assembly (AIA) or Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We report the following new phenomena: (1) Repeated injections of chromospheric material appearing as 10830 Å absorption are squirted out from inter-granular lanes with a period of ∼ 5 minutes. (2) EUV emissions are found to be periodically modulated with similar periods of ∼ 5 minutes. (3) Around the injection area where 10830 Å absorption is enhanced, both EUV emissions and strength of the magnetic field are remarkably stronger. (4) The peaks on the time profile of the EUV emissions are found to be in sync with oscillatory peaks of the stronger magnetic field in the region. These findings may give a series of strong evidences supporting the scenario that coronal heating is powered by magneto-acoustic waves.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/2041-8213/ac447c
