We have used the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) low-resolution and medium-resolution spectroscopic surveys to explore the chromospheric statistical properties and variations of M stars. There are 738,477 LAMOST low-resolution spectra of 622,523 M stars. We have calculated equivalent widths of the Ca ii H&K, Hα, Hβ, Hγ, Hδ, He i D3, and Ca ii infrared triplet lines. Based on the Hα EWs, we found that 33,374 objects showed Hα emissions. We revised the relationship between the active fraction and spectral subtype, and confirmed that the active fractions increased from M0 to M3, and possibly declined from M4 to subsequent types. Among 86,005 objects with repeated spectra, 19,422 objects showed Hα variations. The variation fraction of stars with M4 and subsequent types with a fully convective envelope was higher than those of M0–M3 with a partially convective envelope. By combining the distances from Gaia, we have determined the positions of the M dwarfs in the catalog for M stars. The active fraction decreased rapidly in the height range of 0–400 pc above and below the Galactic plane, and maintained a steady trend in 400–1000 pc. We cross-matched the M catalog of the LAMOST low-resolution survey with LAMOST medium-resolution spectra. We obtained 272,181 spectra of 13,355 M objects and calculated the Hα EWs. Among them, 3813 stars show variations, which might be caused by chromospheric activity evolution with orbital phase or time. The Hα emission for 972 objects shows variations over short and long timescales, especially on short timescales of 20 minutes.

我们使用大天区多目标光纤光谱望远镜 (LAMOST) 低分辨率和中分辨率光谱调查来探索 M 星的色球统计特性和变化。有 738,477 个 LAMOST 低分辨率光谱，由 622,523 M 颗恒星组成。我们已经计算了 Ca ii H&K、H α、H β、H γ、H δ、He i D3 和​​ Ca ii红外三重线的等效宽度。基于 H α EW，我们发现 33,374 个物体显示 H α排放。我们修正了活动部分与光谱亚型之间的关系，并确认活动部分从 M0 增加到 M3，并可能从 M4 下降到后续类型。在86,005个重复光谱的物体中，19,422个物体显示H α变化。具有完全对流包络的 M4 及后续类型的恒星的变异分数高于具有部分对流包络的 M0-M3 的恒星。通过结合到盖亚的距离，我们已经确定了 M 矮星在 M 星目录中的位置。在银面上下0-400 pc高度范围内，活跃度迅速下降，并在400-1000 pc保持稳定趋势。我们将 LAMOST 低分辨率调查的 M 目录与 LAMOST 中分辨率光谱进行了交叉匹配。我们获得了 13,355 M 个物体的 272,181 个光谱并计算了 H α EW。其中，3813颗恒星出现变化，这可能是色层活动随轨道相位或时间演化引起的。H α 972 个物体的发射在短期和长期的时间尺度上显示出变化，特别是在 20 分钟的短时间尺度上。