Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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STELLAR MAGNETIC ACTIVITY MEASURE BASED ON IUE MG II H+K EMISSION LINES OF MAIN-SEQUENCE G STARS

  • 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)
  • Received : 2021.04.08
  • Accepted : 2022.04.12
  • Published : 2022.04.30
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Abstract

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.

Keywords

Acknowledgement

This work was supported by the research fund of Chungnam National University.

References

  1. Buccino, A. P. & Mauas, J. D. 2008, Mg II h + k emission lines as stellar activity indicators of main-sequence F-K stars, A&A, 483, 903 https://doi.org/10.1051/0004-6361:20078925
  2. Choi, H., Lee, J., Oh, S., Kim, Bo., Kim, H., & Yi, Y. 2015, Cycle Length Dependence of Stellar Magnetic Activity and Solar Cycle 23, ApJ, 802, 67 https://doi.org/10.1088/0004-637X/802/1/67
  3. Flower, P. J. 1996, Transformations form theoretical Hertzsprung-Russell Diagrams to color-magnitude diagrams: Effective Temperatures, B - V colors, and bolometric corrections, ApJ, 469, 355 https://doi.org/10.1086/177785
  4. Friis-Christensen, E., & Lassen, K. 1991, Length of the Solar Cycle: An Indicator of Solar Activity Closely Associated with Climate, Sci, 254, 698 https://doi.org/10.1126/science.254.5032.698
  5. Metcalfe, T. S., Dziembowski, W. A., Judge, P. G., & Snow, M. 2007, Asteroseismic signatures of stellar magnetic activity cycles, MNRAS, 379, L16 https://doi.org/10.1111/j.1745-3933.2007.00325.x
  6. Middelkoop, F. 1982, Magnetic structure in cool stars. IV - Rotation and CA II H and K emission of main-sequence stars, A&A, 107, 31
  7. Olmedo, M., ChAvez, M., Bertone, E., & Voctor De La Luz 2013, Mg II h+k flux - Rotational period correlation for G-type stars, PASP, 125, 1436 https://doi.org/10.1086/674332
  8. Oranje, B. J., Zwaan, C, & Middelkoop, F. 1982, Magnetic structure in cool stars: V. Chromospheric and Transition-region Emission from Giants, A&A, 110, 30
  9. Oranje, B. J., & Zwaan, C. 1985, Magnetic structure in cool stars: VII. The Mg II h and k surface fluxes in relation to the Mt. Wilson photometric Ca II H and K measurements, A&A, 147, 265
  10. Rutten, R. G. M. 1984, Magnetic structure in cool stars: VII. Absolute surface fluxes in Ca II H and K line core, A&A, 130, 353
  11. Rutten, R. G. M, Schrijver, C. J., Lemmens, A. F. P., & Zwaan, C. 1991, Magnetic structure in cool stars: XVII. Minimum radiative losses from the outer atmosphere, A&A, 252, 203
  12. Schrijver, C. J. 1987, Magnetic structure in cool stars: XI. Relations between radiative fluxes measuring stellar activity, and evidence for two components in stellar chromospheres, A&A, 172, 111
  13. Schrijver, C. J., Dobson. A. K., & Radick, R. R. 1992, Nearly simultaneous observations of chromospheric and coronal radiative losses of cool stars, A&A, 258, 432
  14. Vaughan, A. H., Preston, G. W., & Wilson, O. C. 1978, Flux measurements of Ca II and K emission, PASP, 90, 267 https://doi.org/10.1086/130324
  15. Wilson, O. C. 1978, Chromospheric variations in main-sequence stars, ApJ, 226, 379 https://doi.org/10.1086/156618