[P-EM11] Frontiers in solar physics

[PEM11-P11] Comparison of multiple chromospheric lines for postflare loops accompanied by a flare

*Junya Natsume¹, Ayumi Asai¹, Satoru Ueno¹, Takato Otsu¹, Kiyoshi Ichimoto^1,2 (1.Graduate School of Science, Kyoto University, 2.Ritsumeikan University)

Keywords:solar flare, stellar flare, flare loop, chromosphere, Sun-as-a-star

Solar/stellar flares are phenomena where magnetic energy is released by magnetic reconnection and brightened over a wide range of electromagnetic waves. While solar flares can be observed in a spatially resolved manner, stellar ones can be observed as a single point and we can obtain spectra or light curves. To understand stellar flares through knowledge of solar physics, an analysis of spatial integration of solar observational data into data mimicking stellar observation (Sun-as-a-star analysis) has been conducted. Flare ribbons are ribbon-like brightening structures in the chromosphere heated by non-thermal particles and thermal flows. Postflare loops are ~10⁴ K plasmas along reconnected magnetic loops which are cooled from 10^6-7 K plasma evaporated by the heating of chromospheric plasma and are observed in the late phase of the flare. In stellar observation, red-shifted brightening components of H-alpha (Ha) line in a flare on an M-type dwarf have been detected and the component in the late phase can be considered as postflare loops. In solar research, Sun-as-a-star analysis of postflare loops in Ha line has revealed that the brightening/darkening components from postflare loops can be detected in Sun-as-a-star data. The chromospheric line used in Sun-as-a-star analysis is mainly H-alpha line like these previous researches. However, the H-alpha line's brightening and darkening actually cancel each other and lose quantitative information about postflare loops. By using multiple chromospheric lines with sensitivity to different physical conditions, we can obtain more information about flare than using a single line. Sun-as-a-star analysis of postflare loops in multiple chromospheric lines has not been conducted and the differences between these lines are not well known. The aim of our research is to investigate the difference in the signal of postflare loops between multiple chromospheric lines and help to understand stellar flares. We observed an X1.6 class flare with postflare loops that occurred in NOAA 13386 on 2023 August 5 by using Domeless Solar Telescope (DST) at Hida Observatory of Kyoto University. Using the horizontal spectrograph on DST, we observed the flare ribbons and the postflare loops in four chromospheric lines simultaneously: Ha, Ca II K (CaK), Ca II 8542 angstroms (CaIR) and He I 10830 angstroms (He). Flare ribbons were observed and postflare loops appeared almost simultaneously as brightening in line centers of these four lines. The brightening of the postflare loops in He disappeared 10 minutes after the postflare loop appeared. Brightening of the postflare loops was detected in the wing images of CaK while darkening of the postflare loops was detected in the wing images of the other lines. The dynamic spectra generated by spatial integration over the postflare loops region show that line centers of the four lines had enhancement at the time postflare loops appeared and the enhancement in He disappeared within 10 minutes. The wings of Ha, CaIR and He had darkening and the wings of CaK had brightening. These signals originated from postflare loops. By spatial integration over the region including postflare loops and flare ribbons, signals coming from postflare loops can be seen. We are going to show a detailed description of the spectra and physical interpretation of the differences in postflare loops among the lines.