[논문]STELLAR MAGNETIC ACTIVITY MEASURE BASED ON IUE MG II H+K EMISSION LINES OF MAIN-SEQUENCE G STARS

Kim, Dowoon; Choi, Hwajin; Yi, Yu

doi:10.5303/jkas.2022.55.2.59

STELLAR MAGNETIC ACTIVITY MEASURE BASED ON IUE MG II H+K EMISSION LINES OF MAIN-SEQUENCE G STARS 원문보기

Journal of the Korean astronomical society = 천문학회지, v.55 no.2, 2022년, pp.59 - 66

Kim, Dowoon (Department of Astronomy and Space Science, Chungnam National University) , Choi, Hwajin (Department of Astronomy and Space Science, Chungnam National University) , Yi, Yu (Department of Astronomy and Space Science, Chungnam National University)

Abstract ▼ AI-Helper

Stellar magnetic activity is important for formulating the evolution of the star. To represent the stellar magnetic activity, the S index is defined using the Ca II H+K flux measure from the Mount Wilson Observatory. Mg II lines are generated in a manner similar to the formation of Ca II lines, which are more sensitive to weak chromospheric activity. Mg II flux data are available from the International Ultraviolet Explorer (IUE). Thus, the main purpose of this study was to analyze the magnetic activity of stars. We used 343 high-resolution IUE spectra of 14 main-sequence G stars to obtain the Mg II continuum surface flux and Mg II line-core flux around 2,800 Å. We calculated S index using the IUE spectra and compared it with the conventional Mount Wilson S index. We found a color (B - V ) dependent association between the S index and the Mg II emission line-core flux. Furthermore, we attempted to obtain the magnetic activity cycles of these stars based on the new S index. Unfortunately, this was not successful because the IUE observation interval of approximately 17 years is too short to estimate the magnetic activity cycles of G-type stars, whose cycles may be longer than the 11 year mean activity cycle of the sun.

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표/그림 (10)

그림 Figure 1. IUE Spectra of four representative stars: from top, HD1835 (G3V), HD10700 (G8,5V), HD20630 (G5Vv) and HD131156A (G8V).
그림 Figure 2. log(F_{cont,Mg II}) vs. B - V for 343 high resolution IUE spectra of 14 main-sequence G stars. The red solid line represents the linear least-squares fitting. The standard deviations of this slope and y-intercept are 0.81, 0.53.
표 Table 1 Main-sequence G stars
그림 Figure 3. The continuum surface flux F_{cont,Mg II} normalized to the averaged continuum surface flux cont,Mg II> vs. B - V for 343 high resolution IUE spectra of 14 mainsequence G stars.
그림 Figure 4. Continuum surface flux F_{cont,Mg II} vs. line-core surface flux F_{Mg II}. The yellow cross indicates B - V < 0.62, the blue cross indicates 0.62 < B - V 0.71, the pink circle indicates B -V = 0.62, and the brown circle indicates B -V = 0.71.
그림 Figure 5. The Mg II line-core fux vs. S index. B - V s are divided similarly to those in Figure 4.
그림 Figure 6. S index of the stars listed in Table 1. Red dots indicate the annual average .
그림 Figure 6. Continued
그림 Figure 6. Continued
그림 Figure 6. Continued

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