Published February 26, 2021 | Version v1
Poster Open

Rotation-Activity Relation of Ca II and Mg I Infrared Emission Lines of Young Stars

  • 1. University of Hyogo
  • 2. National Astronomical Observatory of Japan

Description

To reveal the detail of the internal structure, the relationship between chromospheric activity and the Rossby number, NR(= rotational period P / convective turnover time τc), has been extensively examined for main-sequence stars. The goal of our work is to apply the same methods to pre-main-sequence (PMS) stars and identify the appropriate model of τc for them. Yamashita et al. (2020) investigated the relationship between NR and strengths of the Ca I\hspace{-.1em}I infrared triplet (λ8498,8542,8662 \angstrom) emission lines of 60 PMS stars. Their equivalent widths are converted into the emission line to the stellar bolometric luminosity ratio (R). The 54 PMS stars have NR<101.0 and show R104.2 as large as the maximum R of the zero-age main-sequence (ZAMS) stars. However, because all R was saturated against NR, it was not possible to estimate the appropriate τc model for the PMS stars. We noticed that Mg I emission lines at 8807.8\angstrom is an optically thin chromospheric line, appropriate for determination of the adequate τc for PMS stars. Using the archive data of the AAT/the University College London Echelle Spectrograph, we investigated the Mg I line of 52 ZAMS stars. After subtracting photospheric absorption component, the Mg I line is detected as an emission line in 45 ZAMS stars, whose RMgI is between 105.9 and 104.1. The Mg I line is not saturated yet in "the saturated regime for the Ca I\hspace{-.1em}I emission lines", i.e. 101.6<NR<100.8. Therefore, the adequate τc for PMS stars can be determined by measuring of their RMgI values. 

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