Gliese 867
Nearest quadruple system with a red dwarf primary star.
Gliese 867, also cataloged as FK Aquarii and FL Aquarii, is a star system 29 light-years (8.9 parsecs) from Earth in the constellation Aquarius. It consists of two binary subsystems, designated Gliese 867 A and Gliese 867 B. This quadruple system ranks as the third-closest of its kind, after Gliese 570 and Mu Herculis, and is the nearest quadruple system whose primary star is a red dwarf. (Two quintuple systems, V1054 Ophiuchi and Xi Ursae Majoris, are closer; the former is composed entirely of red dwarfs.)
The two main components, A and B, are separated by 24.5 arcseconds, which corresponds to a projected distance of 216 astronomical units. Both are spectroscopic binaries and are classified as flare stars and BY Draconis variables; their flare activity has been known since 1978.
Gliese 867 A, known as FK Aquarii, is a close binary with an orbital period of 4.1 days. Its companion is designated Gliese 867 C. Both stars are red dwarfs, each about half the mass of the Sun. This subsystem was identified as a spectroscopic binary in 1965, originally listed under the Durchmusterung designation BD−21°6267A, and has since been characterized by Gaia astrometry. Both stars are magnetically active, possessing strong dipolar magnetic fields similar to those found in lower-mass, fully convective red dwarfs. As of 2024, the primary is the most massive red dwarf known to host such a magnetic field.
Gliese 867 B, or FL Aquarii, is a close binary with an orbital period of 1.8 days, confirmed as a spectroscopic binary in 2014. Its primary is a red dwarf, while its companion, Gliese 867 D, has a minimum mass of 61 ± 7 Jupiter masses, placing it in the brown dwarf range.
- Distance
- 29 light-years (8.9 parsecs)
- Constellation
- Aquarius
- Quadruple system rank
- third-nearest quadruple system
- Separation between a and b
- 24.5 arcseconds (216 AU projected)
- Orbital period of gliese 867 a
- 4.1 days
- Orbital period of gliese 867 b
- 1.8 days
- Minimum mass of gliese 867 d
- 61±7 Jupiter masses
Lore & Background
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, known to be flare stars since 1978. Gliese 867 A, also known as FK Aquarii, is a close binary orbiting every 4.1 days; its companion is 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, with 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. Gliese 867 B, also known as FL Aquarii, is a close binary orbiting every 1.8 days, found to be a spectroscopic binary in 2014. Its primary is a red dwarf, while the companion, Gliese 867 D, has a minimum mass of only 61±7 Jupiter masses, and so may be a brown dwarf.
Reader's Guide
Gliese 867 is notable as the third-nearest quadruple star system and the nearest such system where the primary star is a red dwarf. Its two binary sub-systems, FK Aquarii and FL Aquarii, are both flare stars and BY Draconis variables, exhibiting magnetic activity and flares observed since 1978. The primary star of FK Aquarii is the most massive red dwarf known as of 2024 to host strong dipolar magnetic fields typical of fully convective stars, making it a key object for studying stellar magnetism. The companion in FL Aquarii, Gliese 867 D, with a minimum mass of 61±7 Jupiter masses, may be a brown dwarf, adding to the system's diversity. The system has been studied via astrometry from the Gaia space telescope and through extensive photometric and X-ray observations, as documented in the referenced literature. Its proximity and complexity make it a valuable laboratory for understanding multiple star systems, flare activity, and magnetic field generation in low-mass stars.
Did You Know?
- Gliese 867 is the third-nearest quadruple system, after Gliese 570 and Mu Herculis.
- Both sub-systems, FK Aquarii and FL Aquarii, are flare stars and BY Draconis variables.
More in Variable Stars, Part 3 1-24
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