The Astrophysical Journal Supplement Series (Jan 2024)

The Near-infrared Ca ii Triplet as a Stellar Activity Indicator: A Library and Comparative Study

  • Xin Huang,
  • Yuji He,
  • Zhongrui Bai,
  • Hailong Yuan,
  • Mingkuan Yang,
  • Ming Zhou,
  • Yiqiao Dong,
  • Mengxin Wang,
  • Han He,
  • Jinghua Zhang,
  • Yaoquan Chu,
  • Yongheng Zhao,
  • Yong Zhang,
  • Haotong Zhang

DOI
https://doi.org/10.3847/1538-4365/ad33bc
Journal volume & issue
Vol. 272, no. 1
p. 6

Abstract

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We have established and released a new stellar index library of the Ca ii triplet, which serves as an indicator for characterizing the chromospheric activity of stars. The library is based on data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Low-Resolution Spectroscopic Survey (LRS) Data Release 9. To better reflect the chromospheric activity of stars, we have defined new indices R and R ^+ . The library includes measurements of R and R ^+ for each Ca ii infrared triplet (IRT) from 699,348 spectra of 562,863 F, G, and K-type solar-like stars with a signal-to-noise ratio higher than 100, as well as the stellar atmospheric parameters and basic information inherited from the LAMOST LRS catalog. We compared the differences between the three individual indices of the Ca ii triplet and also conducted a comparative analysis of ${R}_{\lambda 8542}^{+}$ to the Ca ii H and K S and ${R}_{\mathrm{HK}}^{+}$ index databases. We observe the fraction of less active stars decreases with T _eff and the fraction of more active stars first decreases with decreasing temperature and turns to increase with decreasing temperature at 5800 K. We also find that a significant fraction of stars that show a high activity index in both Ca ii H and K and IRT are binaries with low activity; some of them could be discriminated in the Ca ii H and K S index and ${R}_{\lambda 8542}^{+}$ space. This new stellar library serves as a valuable resource for studying chromospheric activity in stars and can be used to improve our comprehension of stellar magnetic activity and other astrophysical phenomena.

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