2022/11/10 by A. Sainz Dalda, Dalda, Alberto Sainz, Bart De Pontieu +1
Computer Science · Energy · Physics and Astronomy · #Astronomy #Astrophysics #Chromosphere #Computational physics #Electron #Electron temperature #FOS: Physical sciences #Flare #K-line #Nuclear physics #Oil, Gas, and Environmental Issues #Optics #Physics #Radiative transfer #Solar Radiation and Photovoltaics #Solar and Space Plasma Dynamics #Solar and Stellar Astrophysics (astro-ph.SR) #Solar flare #Spectral line #Stars #Thermodynamic equilibrium #Thermodynamics #Turbulence
paper · pdf · doi:10.48550/arxiv.2211.05459
openalex publication_date 2022/11/10 · openalex created_date 2022/11/16 · openalex updated_date 2026/07/28
The flare activity of the Sun has been studied for decades, using both space- and ground-based telescopes. In particular, the Interface Region Imaging Spectrograph (IRIS) provides unique diagnostics to investigate the thermodynamics of flares in the solar atmosphere. The Mg II h&k and Mg II UV triple lines provide key information about the thermodynamics of low to upper chromosphere, while the C II 1334 & 1335 AA lines cover the upper-chromosphere and low transition region. The Mg II h&k and Mg II UV triplet lines show a peculiar, pointy shape before and during the flare activity. The physical interpretation that can explain these profiles has remained elusive. In this paper, we show the results of a non-LTE inversion of such peculiar profiles. To better constrain the atmospheric conditions, the Mg II h&k and Mg II UV triple lines are simultaneously inverted with the C II 1334 & 1335 AA lines. This combined inversion leads to more accurate derived thermodynamic parameters, especially the temperature and the turbulent motions (micro-turbulence velocity). We use the inversion code STiC to look for the best fit between the observed profile and a synthetic profile obtained by solving the radiative transfer problem considering non-local thermodynamic equilibrium and partial frequency redistribution of the radiation due to scattered photons. We are able to conclude that these unique, pointy profiles are associated with a simultaneous increase of the temperature and the electron density in the chromosphere, while the micro-turbulence velocity has values between 5-15 km/s, which seem to be more realistic values than the ones suggested in previous work. More importantly, the line-of-sight velocity shows a large gradient along the optical depth in the high chromosphere. This seems to be the parameter that gives the pointy aspect to these profiles.