2017/10/11 by Vincenzo Capparelli, Francesca Zuccarello, Paolo Romano +8 · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Balmer series #Chromosphere #Flare #Intensity (physics) #Radiative transfer #Solar and Space Plasma Dynamics #Solar flare #Solar physics #Spectrometer #Stellar, planetary, and galactic studies #Wavelength #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/aa9187
14 pages, 17 figures
arxiv created 2017/10/11 · openalex created_date 2017/10/20 · openalex publication_date 2017/11/14 · arxiv updated 2017/11/29 · openalex updated_date 2026/08/05
Abstract The hydrogen Balmer series is a basic radiative loss channel from the flaring solar chromosphere. We report here on the analysis of an extremely rare set of simultaneous observations of a solar flare in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> </mml:math> lines, at high spatial and temporal resolutions, that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22) made at various wavelengths along the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> line profile by the Interferometric Bidimensional Spectrometer (IBIS) and in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> </mml:math> with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband imager are analyzed to obtain the intensity evolution. The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> </mml:math> intensity excesses in three identified flare footpoints are well-correlated in time. We examine the ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>β</mml:mi> </mml:math> flare excess, which was proposed by previous authors as a possible diagnostic of the level of electron-beam energy input. In the stronger footpoints, the typical value of the the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> /H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>β</mml:mi> </mml:math> intensity ratio observed is ∼0.4–0.5, in broad agreement with values obtained from a RADYN non-LTE simulation driven by an electron beam with parameters constrained (as far as possible) by observation. The weaker footpoint has a larger <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> /H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>β</mml:mi> </mml:math> ratio, again consistent with a RADYN simulation, but with a smaller energy flux. The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> line profiles observed have a less prominent central reversal than is predicted by the RADYN results, but can be brought into agreement if the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:math> -emitting material has a filling factor of around 0.2–0.3.