Gliese 867
Gliese 867 is a quadruple star system located away in the constellation Aquarius. It is composed of two binary sub-systems, Gliese 867 A & B, also known by their variable star designations FK Aquarii and FL Aquarii. Gliese 867 is the third-nearest quadruple system, after Gliese 570 and Mu Herculis, and the nearest such system where the primary star is a red dwarf. There are two closer quintuple systems, V1054 Ophiuchi and Xi Ursae Majoris, the former composed entirely of red dwarfs.
System
Gliese 867 A & B are separated by 24.5 arcseconds, corresponding to a projected distance of 216 AU. Both are spectroscopic binaries. Gliese 867 A & B are both flare stars and BY Draconis variables. They have been known to be flare stars since 1978.
Gliese 867 A (FK Aquarii)
Gliese 867 A, also known as FK Aquarii, is a close binary orbiting every 4.1 days. The companion star is also called Gliese 867 C. Both stars are red dwarfs around half the mass of the Sun. The system has been known to be a spectroscopic binary since 1965, at that time referred to by its Durchmusterung designation BD−21°6267A. It has also been characterized by astrometry from the Gaia space telescope.Both stars are magnetically active, and have strong dipolar magnetic fields resembling those found in lower-mass, fully convective red dwarfs. The primary star is the most massive red dwarf known to host this type of magnetic field as of 2024.