Published online by Cambridge University Press: 26 May 2016
We present recent X-ray and optical observations of five M-type giants which were detected as strong X-ray sources. One of these stars, HR 5512, shows short-term variations in both X-ray flux as well as in the shape of the Hα and Ca ii H+K lines, and it rotates much faster than M-type giants usually do. No indication of binarity has been found for this star. We propose that the X-ray emission of HR 5512 is related to a large degree of stellar activity. For two other stars (15 Tri, HR 7547) radial velocity observations seem to indicate spectroscopic binarity.
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