We present spectroscopic observations of two halo M subdwarfs that have Hα emission lines. We show that in both cases close companions are the likely cause of the chromospheric activity in these old, metal-poor stars. We argue that Gl 781A's unseen companion is most likely a cool helium white dwarf. Gl 455 is a near–equal-mass M subdwarf (sdM) system. Gl 781A is rapidly rotating, with v sin i ≈ 30 km s-1. The properties of the chromospheres and X-ray coronae of these systems are compared with M dwarfs with emission (dMe's). The X-ray hardness ratios and optical chromospheric line emission ratios are consistent with those seen in dMe stars. Comparison with active near–solar metallicity stars indicates that, despite their low metallicity ([M/H] ≈ -1.2), the sdMe stars are roughly as active in both X-rays and chromospheric emission. Measured by LX/Lbol, the activity level of Gl 781A is no more than a factor of 2.5 subluminous with respect to near–solar-metallicity stars.
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机译：我们介绍了具有Hα发射谱线的两个晕M亚矮的光谱观察。我们表明，在这两种情况下，这些金属贫乏的旧恒星中，色球活动的可能原因是近邻。我们认为，Gl 781A看不见的同伴很可能是冷氦白矮星。 GL 455是质量近似的M亚矮（sdM）系统。 GL 781A正在快速旋转，其中v sin i≈30 km s-1。将这些系统的色球层和X射线日冕的特性与带有发射的M个矮星（dMe's）进行了比较。 X射线硬度比和光学色球线发射比与dMe恒星中的一致。与活跃的近太阳金属星比较，表明，尽管它们的金属性较低（[M / H]≈-1.2），但sdMe恒星在X射线和色球发射中的活性大致相同。用LX / Lbol测得，相对于近太阳金属星，Gl 781A的活动水平不超过2.5次发光的因数。
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