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Abstract We analyze a catalog comprising 781,232 spectra from 641,095 M dwarf stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution spectroscopic data release 9. Based on the equivalent width of the H α line, we ascertain the activity properties of the stars, identifying a total of 107,134 active stars, with 31,175 exhibiting H α variations. Furthermore, we establish a positive correlation between starspot activity from Transiting Exoplanet Survey Satellite light curves, and chromospheric activity observed through LAMOST spectra on M dwarf stars. Utilizing LAMOST and Gaia data, we map the two-dimensional distribution of active fractions across all M dwarfs in the Milky Way based on H α and H β lines, confirming a decrease in the active fraction as the distance above the Galactic disk increases. Additionally, we investigate the relationship between chromospheric activity and absolute height above the Galactic disk in various M subtypes. Our findings reveal distinct trends: for M0 to M5 dwarf stars, the active fraction of H α and H β lines rapidly decreases within the 0–300 pc range. In the 300–500 pc range, M0 to M4 dwarf stars exhibit a gradual increase, followed by a decrease in the 500–1000 pc range. Conversely, M5 dwarf stars show no significant gradual increase in the 300–500 pc range and decrease in the 500–1000 pc range. More data will be needed to confirm the phenomenon.
Li et al. (Tue,) studied this question.