EZ Aquarii
Triple red dwarf flare star system 11.1 light-years away.
EZ Aquarii is a triple star system in the constellation Aquarius, about 11.1 light-years from the Sun. It goes by several other names, including Luyten 789-6, Gliese 866, and LHS 68. The system is a variable star, brightening in flares and showing smaller changes as it rotates. The combined mass of all three stars is 0.3262 solar masses, and each star is close to the minimum mass needed to sustain hydrogen fusion.
All three stars are M-type red dwarfs. The pair known as EZ Aquarii AC orbit each other every 3.8 days, separated by 0.03 AU. This inner pair, in turn, orbits EZ Aquarii B once every 823 days. The A and B components together emit X-rays. The arrangement of the inner binary could allow a circumbinary planet to exist near their habitable zone, though no exoplanets have been found. EZ Aquarii is moving toward the Solar System and will reach its closest point—about 8.2 light-years away—in roughly 32,300 years. Its nearest current neighbor is Lacaille 9352, about 4.1 light-years away.
The brighter resolved star, EZ Aquarii A, is itself a spectroscopic binary made of two red dwarfs. They orbit each other every 3.78652 days in a perfectly circular path. The primary, component Aa, is an M5V star with a mass of 0.1187 solar masses and an absolute magnitude of 15.33 at 5500 Angstroms, making it the brightest of the three. The secondary, component Ab, is likely an MV red dwarf with a mass of 0.0930 solar masses and an absolute magnitude of 17.37, the dimmest of the trio.
EZ Aquarii B is less well understood. It is probably an MV red dwarf with a mass of 0.1145 solar masses. It orbits the spectroscopic pair every 822.6 days on an eccentric path (eccentricity 0.439). Its absolute magnitude is 15.58.
The system’s high proper motion may have been discovered by Willem Jacob Luyten using an automated photographic plate scanner.
- Distance
- 11.1 light-years (3.4 parsecs)
- Constellation
- Aquarius
- Aggregate mass
- 0.3262±0.0018 solar masses
- Variable star designation
- EZ Aquarii (assigned 1978)
- Flare star announced by
- William E. Kunkel (1972)
- Nearest neighbour
- Lacaille 9352 at about 4.1 ly (1.3 pc)
- Minimum distance future
- about 8.2 ly (2.5 pc) in about 32,300 years
Lore & Background
William E. Kunkel announced that Luyten 789-6 was a flare star in 1972, after having observed seven flares. It was given its variable star designation, EZ Aquarii, in 1978. The high proper motion of EZ Aquarii may have been discovered by Willem Jacob Luyten with his automated photographic plate scanner.
The system consists of three M-type red dwarfs. The pair EZ Aquarii AC form a spectroscopic binary with a 3.8-day orbit and a 0.03 AU separation. This pair share an orbit with EZ Aquarii B that has an 823-day period. The A and B components together emit X-rays. The brighter resolved star (EZ Aquarii A) is itself a spectroscopic binary of two red dwarfs orbiting every 3.78652±0.00001 days with a circular orbit. The primary (Aa) is type M5V with mass 0.1187±0.0011 solar masses and absolute magnitude 15.33; the secondary (Ab) is likely type MV with mass 0.0930±0.0008 solar masses and absolute magnitude 17.37, making it the dimmest of the three. EZ Aquarii B is likely type MV with mass 0.1145±0.0012 solar masses, orbiting the inner pair with a period of 822.6±0.2 days and eccentricity 0.439±0.001, and has absolute magnitude 15.58.
Reader's Guide
EZ Aquarii is significant as a nearby triple star system whose components are all near the hydrogen burning mass limit, making it a valuable laboratory for studying low-mass stellar evolution and flare activity. Its variability, discovered by Kunkel in 1972, includes both flares and rotational brightness changes, and it was formally designated a variable star in 1978. The system's configuration—a close spectroscopic binary (AC) orbited by a third star (B)—may permit a circumbinary planet near the habitable zone, though no exoplanets have yet been observed. EZ Aquarii is approaching the Solar System and will reach a minimum distance of about 8.2 light-years in roughly 32,300 years. Its current nearest neighbor is Lacaille 9352 at about 4.1 light-years. The system's high proper motion was likely discovered by Willem Jacob Luyten. The A and B components emit X-rays, and the orbital parameters of all three stars are well measured, providing constraints on dynamical models of multiple star systems.
Did You Know?
- EZ Aquarii is also known as Luyten 789-6, Gliese 866, and LHS 68.
- The system's aggregate mass is 0.3262±0.0018 solar masses.
- All three components are M-type red dwarfs with masses close to the hydrogen burning mass limit.
- The inner binary pair (AC) orbits every 3.8 days with a separation of 0.03 AU.
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