Abstract
We report the discovery of a new short-period, main-sequence, chromospherically active late-type binary system. EUV observations performed by the ROSAT Wide Field Camera have identified the late-type star GL 841A as a possible very active star by virtue of a large EUV-to-bolometric flux ratio. Subsequent optical observations at the wavelengths of the Hα and Ca II H and K lines have confirmed this, and also the binary nature of the system. An orbital period of 1.124 d, an inclination of 28° and a mass ratio of approximately unity are deduced from radial velocity data. Both components show Hα in emission. The photometric colours and absolute magnitude indicate that the component stars are both spectral class dM3-5e. A flare is observed in the Hα emission profile and is attributed to flares on at least one and possibly both the component stars within the space of a few hours. The GL 841A system is similar in many respects to the young eclipsing binary YY Gem but, because GL 841B (the common proper motion, visual binary companion) is a cool dQ7 white dwarf, an age of at least 2 ×109 yr is deduced.
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