Magnetic Activity in M-type Stars Based on LAMOST DR11 and TESS Observations

Abstract We have used 898,351 M-type stellar spectra released by Large Sky Area Multi-Object Fiber Spectroscopic Telescope DR11 to calculate the equivalent width of the Ca II infrared triplet (IRT) lines, the residual chromospheric emission, and the parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>8542</mml:mn> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> , which is defined as the ratio of the luminosity of the 8542 Å line to the stellar bolometric luminosity. The chromospheric activity of M dwarfs reaches its maximum around an effective temperature of 3700 K, corresponding to a spectral type of approximately M6. The stellar photospheric activity begins to become significant at around 3800 K, and the trend gradually becomes weaker when approaching 3200 K, which may be due to the influence of the magnetic activity saturation zone. Furthermore, metallicity also influences the intensity of the chromospheric activity. We found that chromospheric and photospheric activity in M dwarfs are correlated, and that both types of activity are influenced by stellar rotation. Additionally, we crossmatched our catalog with the Transiting Exoplanet Survey Satellite and identified 23,079 flare events from 3280 stars. Our results show that the majority of the M dwarf flare radiation energy is below 10 36 erg, and the flare duration and energy of nearly all spectral types follow a power-law distribution, i.e., <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfrac> <mml:mrow> <mml:mi>d</mml:mi> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>d</mml:mi> <mml:mi>E</mml:mi> </mml:mrow> </mml:mfrac> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mi>a</mml:mi> </mml:mrow> </mml:msup> </mml:math> with α = 2. For the cumulative flare frequency distribution’s power-law index, we found the range to be between 1.44 and 2. We found that the power-law index α for fully convective M-type stars is approximately 1.61 ± 0.08, while for non–fully convective M-type stars, it is around 1.78 ± 0.11.