Luyten 726-8

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Luyten 726-8 A/B
Observation data
Epoch J2000
Constellation
(pronunciation)		 Cetus
Right ascension 01h 39m 01.3s
Declination -17° 57' 01"
Apparent magnitude (V) 12.54/12.99
Characteristics
Spectral type M5.5 V/M6 V
U-B color index 1.10/?
B-V color index 1.87/?
Variable type Flare stars
Astrometry
Radial velocity (Rv) +29.0 km/s
Proper motion (μ) RA: 3321 mas/yr
Dec.: 562 mas/yr
Parallax (π) 373.70 ± 2.70 mas
Distance 8.73 ± 0.06 ly
(2.68 ± 0.02 pc)
Absolute magnitude (MV) 14.92/15.37
Visual binary orbit
Companion Luyten 726-8 B
Period (P) 26.5 yr
Semimajor axis (a) 1.95"
Eccentricity (e) 0.62
Inclination (i) 127.3°
Longitude of the node (Ω) 150.5°
Periastron epoch (T) 1971.91
Details
Mass 0.10/0.10 M☉
Radius 0.14/0.14 R☉
Luminosity 0.00006/0.00004 L☉
Temperature 2,670 K
Age ?/? years
Other designations
BL Ceti/UV Ceti, GCTP 343.10 A/B, LHS 9/10, GJ 65 A/B

Luyten 726-8 is a binary star system that is one of Earth's nearest neighbors, the closest star in the constellation Cetus. One of its components is the well-known flare star UV Ceti (Luyten 726-8 B).

Although UV Ceti was not the first flare star discovered, it is the most prominent example of such a star, and in fact flare stars are sometimes called "UV Ceti variables". It goes through fairly extreme changes of brightness: for instance, in 1952, its brightness increased by 75 times in only 20 seconds. UV Ceti is a red dwarf of spectral type M6.0e.

The other component is BL Ceti (Luyten 726-8 A), a red dwarf of spectral type M5.5e. It is also a flare star, but not nearly as remarkable or extreme in its behavior as UV Ceti.

The two stars are of nearly equal brightness, with visual magnitudes of 15.3 and 15.8 as seen from Earth. They orbit one another every 26.5 years. The distance between the two stars varies from 2.1 to 8.8 Astronomical units. Luyten 726-8 is approximately 2.63 pc or 8.57 light-years from Earth's Solar System, in the constellation Cetus, and is thus the sixth-closest star system to Earth. Its own nearest neighbour is Tau Ceti, 0.88 pc or 2.87 ly away from it.

BL Ceti (Luyten 726-8 A) is also catalogued as G 272-061.

[edit] Discovery

The star system was discovered in 1948 by Willem Jacob Luyten in the course of compiling a catalogue of stars of high proper motion; he noted its exceptionally high proper motion of 3.37 arcsec annually and catalogued it as Luyten 726-8. Soon after it was discovered that the fainter B component of this system was a flare star, and it was accordingly given the variable star designation UV Ceti.

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