Stellar magnetic activity in Earth 2.0 candidates based on LAMOST DR10

Abstract

Aims. Stellar chromospheric activity can impact the search for exoplanets. Earth 2.0 (ET 2.0) is a space telescope designed for exoplanet detection. In this work, we survey the stellar chromospheric activity in the ET 2.0 target regions to enhance the detection rate of exoplanets. Methods. This work uses Hα and Ca II H&K lines as indicators of chromospheric activity and conducts a survey of stellar chromospheric activity in the ET 2.0 target regions using LAMOST low- and medium-resolution spectra. After cross-referencing with the ET 2.0 input catalog, we obtained over 349 000 low-resolution spectra and over 30 000 medium-resolution spectra from LAMOST. We quantified the chromospheric activity intensity for all spectra and selected the results for those with a signal-to-noise ratio (S/N) above 10 for further studies of the chromospheric activity. The quantification standards include equivalent width (EW) and the ratio of bolometric luminosity to the corresponding spectral line luminosity (L_Hα/L_bol, L_CaH/L_bol, L_CaK/L_bol, L_HK/L_bol). Results. Utilizing Hα and Ca II H&K lines, we evaluated the chromospheric activity for over 320 000 and 110 000 spectra based on LAMOST low-resolution spectra, respectively. In addition, we evaluated chromospheric activity for 34000 spectra using Hα lines based on medium-resolution spectra. We selected samples that are suitable for exoplanet studies, based on Hα and Ca II H&K lines. Additionally, we explored 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 terms of their relationship between stellar activity and Rossby number (Ro), namely: saturated and unsaturated. We determined a critical Ro in the range of 0.09–0.12 using the r-band spectra of 11 921 stars and u-band spectra of 6120 stars. Moreover, we observe that Ca II H&K lines exhibit greater sensitivity to Ro in the unsaturated region, compared to Ha line measurements. Lastly, we have established positive correlations between various activity indicators, including R'_CaK, R'_CaH, R'_HK, and R'_Hα.