Investigating the emission mechanism of the Fe K; α; and L; α; lines of stellar flares on RS CVn-type stars Journal Article uri icon

Overview

abstract

  • Abstract; ; The low-ionized Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; fluorescence line (; ; ; ; tilde; ; ; ∼; ; $sim$; ; ; 6.4 keV) has been observed during both solar and stellar flares. The emission mechanism of the Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; line has been attributed to the photoionization of neutral or low-ionized iron in the photosphere by coronal X-rays. Alternatively, some studies have suggested that collisional ionization by nonthermal electrons may also contribute. Determining whether photoionization or collisional ionization dominates is important because the Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; line has the potential to probe the spatially unresolved geometry of stellar flare loops. RS CVn-type stars are magnetically active systems that produce powerful superflares exceeding; ; ; ; 10 Superscript 35; ; ; ; 10; ; 35; ; ; ; $10^{35}$; ; ; erg, providing X-ray spectra of stellar flares with high photon statistics. In this proceeding, we summarize the results of our systematic analysis of the Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; line in RS CVn-type stars (Inoue et al. 2025). We identified 25 new Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; detections and found a positive correlation between the Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; line luminosity (; ; ; ; upper L Subscript normal upper K alpha; ; ; ; L; ; ; K; α; ; ; ; ; $L_{mathrm{K alpha}}$; ; ; ) and the 7.11-20 keV thermal plasma luminosity (; ; ; ; upper L Subscript normal upper H normal upper X normal upper R; ; ; ; L; ; ; H; X; R; ; ; ; ; $L_{mathrm{HXR}}$; ; ; ), with a power-law index of; ; ; ; 0.86 plus or minus 0.46; ; ; 0.86; ±; 0.46; ; $0.86 pm 0.46$; ; ; (i.e.,; ; ; ; upper L Subscript normal upper K alpha Baseline proportional to upper L Subscript normal upper H normal upper X normal upper R Superscript 0.86 plus or minus 0.46; ; ; ; L; ; ; K; α; ; ; ; ∝; ; L; ; ; H; X; R; ; ; ; 0.86; ±; 0.46; ; ; ; $L_{mathrm{K alpha}} propto L_{mathrm{HXR}}^{0.86pm0.46}$; ; ; ), and a negative correlation between the Fe K; ; ; ; alpha; ; ; α; ; $alpha$; ; ; line equivalent width (; ; ; ; normal upper E normal upper W Subscript normal upper K alpha; ; ; ; ; E; W; ; ; ; K; α; ; ; ; ; $mathrm{EW}_{mathrm{K alpha}}$; ; ; ) and the 7.11; ; ; ; minus; ; ; −; ; $-$; ; ; 20 keV thermal plasma luminosity with its powerlaw index of; ; ; ; negative 0.27 plus or minus 0.10; ; ; −; 0.27; ±; 0.10; ; $-0.27 pm 0.10$; ; ; (i.e.,; ; ; ; normal upper E normal upper W Subscript normal upper K alpha Baseline proportional to upper L Subscript normal upper H normal upper X normal upper R Superscript negative 0.27 plus or minus 0.10; ; ; ; ; E; W; ; ; ; K; α; ; ; ; ∝; ; L; ; ; H; X; R; ; ; ; −; 0.27; ±; 0.10; ; ; ; $mathrm{EW}_{mathrm{K alpha}} propto L_{mathrm{HXR}}^{-0.27pm0.10}$; ; ; ). These results support the dominance of photoionization from a new perspective that has not previously been explored in the context of stellar flares.;

publication date

  • October 1, 2025

Date in CU Experts

  • October 15, 2026 7:57 AM

Full Author List

  • Inoue S; Enoto T; Notsu Y; Iwakiri WB; Kimura T; Uchida H; Hamaguchi K; Namekata K; Arzoumanian Z; Gendreau K

author count

  • 15

Other Profiles

International Standard Serial Number (ISSN)

  • 1743-9213

Electronic International Standard Serial Number (EISSN)

  • 1743-9221

Additional Document Info

start page

  • 129

end page

  • 134

volume

  • 21

issue

  • S400