M dwarfs dominate the stellar population, accounting for three of every four stars, the nearest of which is Proxima Centauri, the closest destination beyond our Solar System. These cool stars span large ranges in luminosities (one ten-thousandth to 6% L⊙) and temperatures (2,100–3,900 K) and have spectra dominated by absorption bands of titanium oxide (TiO) and, for the latest spectral types, vanadium oxide (VO). They have masses that span 0.075 to 0.61 M⊙, a factor of eight, which is comparable with a spread in masses for dwarf types mid-B through K. Unlike these more massive stars, in the age of the Universe no M dwarfs have evolved in any significant way. M dwarf systems are multiple roughly one-quarter of the time, with the closest binaries found in orbits that have been circularized via tides for orbital periods of about one week. Unlike any other type of main sequence star, there is a gap in the distribution of M dwarfs near masses of 0.35 M⊙ that pinpoints the separation of partially and fully convective stars, yet both types of M dwarfs are often active, showing both Hα in emission and flares. Many planets are found orbiting M dwarfs, and most of them are terrestrial or neptunian in size, rather than jovian, yet much more work remains to be done to characterize the exoplanet population. Overall, the Solar Neighborhood is dominated by M dwarfs that are likely orbited by many small, as yet unseen, planets—some of which may harbor life very near to that in our Solar System: ▪M dwarfs account for three of every four stars.▪M dwarf counts increase all the way to the end of the main sequence.▪M dwarfs are partially radiative at high masses and fully convective at low masses.

中文翻译：

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M 小矮人的性格


M 矮星在恒星中占主导地位，占四颗恒星中的三颗，其中最近的是比邻星，它是我们太阳系之外最近的目的地。这些冷星的光度范围很广（万分之一到 6% L⊙）和温度 （2,100–3,900 K），光谱以氧化钛 （TiO） 的吸收带为主，对于最新的光谱类型，还包括氧化钒 （VO）。它们的质量跨度为 0.075 至 0.61 M⊙，是 8 倍，这与 B 到 K 中矮人类型的质量分布相当。与这些质量更大的恒星不同，在宇宙时代，没有 M 矮星以任何显着的方式演化。M 矮星系统大约有四分之一的时间是多重的，最近的双星是在轨道上发现的，这些轨道已经通过潮汐循环了大约一周。与任何其他类型的主序星不同，在质量为 0.35 M 附近⊙ 的 M 矮星的分布存在差距，这可以精确地指出部分对流恒星和全对流恒星的分离，但两种类型的 M 矮星通常都是活跃的，在发射和耀斑中都显示出 Hα。许多行星被发现围绕 M 矮星运行，其中大多数的大小是类地或海王星，而不是木星，但要描述系外行星群的特征，还有很多工作要做。总体而言，太阳邻域以 M 矮星为主，它们可能由许多尚未见过的小行星围绕运行，其中一些行星的生命可能非常接近我们太阳系中的行星：▪M 矮星占四颗恒星中的三颗。▪M 矮星的数量一直增加，直到主序列的末尾。▪M 矮星在高质量时部分辐射，在低质量时完全对流。