Earth 2.0 candidates stellar magnetic activity

The quantification standards include equivalent width (EW) and the ratio of bolometric luminosity to the corresponding spectral line luminosity (L_Halpha_/L_bol_, L_CaH_/L_bol_, L_CaK_/L_bol_, L_HK_/L_bol_). Utilizing Halpha and CaII H&K lines, we evaluate chromospheric activity for over 320000 and 110000 spectra based on LAMOST low-resolution spectra, respectively. Additionally, we evaluated chromospheric activity for 34000 spectra using Halpha lines based on medium-resolution spectra.

And select samples suitable for exoplanet studies based on Halpha and CaII H&K lines. Additionally, we explore the relationship between stellar activity observed by LAMOST and rotation periods obtained from Kepler and TESS surveys. Our findings confirm the presence of two distinct regions in the relationship between stellar activity and Rossby number (Ro): saturated and unsaturated.

We determined a critical Ro in the range of 0.09 to 0.12 using r-band spectra of 11921 stars and u-band spectra of 6120 stars. Moreover, we observe that CaII H&K lines exhibit greater sensitivity to Ro in the unsaturated region compared to Halpha line measurements. Lastly, we establish positive correlations between various activity indicators, including R'_CaK_, R'_CaH_, R'_HK_ and R'_Halpha_.