EQ Pegasi

EQ Pegasi (also known as Gliese 896) is a nearby binary system of two red dwarfs. Both components are flare stars, with spectral types of M4Ve and M6Ve respectively, and a current separation between the components of 5.8 arcseconds. The system is at a distance of 20.4 light-years, and is 950 million years old.^[10] The primary star is orbited by one known exoplanet.^[4]

EQ Pegasi

EQ Location of EQ Pegasi in the constellation Pegasus
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Pegasus
EQ Pegasi A
Right ascension	23h 31m 52.17385s[1]
Declination	+19° 56′ 14.1304″[1]
Apparent magnitude (V)	10.38 (min)[2]
EQ Pegasi B
Right ascension	23h 31m 52.57534s[3]
Declination	+19° 56′ 14.0050″[3]
Apparent magnitude (V)	12.58 (min)[2]
Characteristics
EQ Pegasi A
Evolutionary stage	red dwarf
Spectral type	M4Ve[2]
Variable type	Flare star[2]
EQ Pegasi B
Evolutionary stage	red dwarf
Spectral type	M6Ve[2]
Variable type	Flare star[2]
Astrometry
EQ Pegasi A
Radial velocity (Rv)	−0.21±0.82[1] km/s
Proper motion (μ)	RA: 578.009(35) mas/yr[1] Dec.: −59.769(23) mas/yr[1]
Parallax (π)	159.6634±0.0341 mas[1]
Distance	20.428 ± 0.004 ly (6.263 ± 0.001 pc)
EQ Pegasi B
Proper motion (μ)	RA: 552.349(55) mas/yr[3] Dec.: 20.275(36) mas/yr[3]
Parallax (π)	159.9085±0.0513 mas[3]
Distance	20.396 ± 0.007 ly (6.254 ± 0.002 pc)
Orbit[4]
Period (P)	83,664.63 ± 1.98 days (229.0613 ± 0.0054 a)
Semi-major axis (a)	5.05797±0.00043" (31.635±0.033 AU)
Eccentricity (e)	0.108047±0.000053
Inclination (i)	130.065±0.010°
Longitude of the node (Ω)	255.0919±0.0034°
Periastron epoch (T)	2,401,891.34±1.19
Argument of periastron (ω) (secondary)	307.1416±0.0045°
Details
A
Mass	0.43599±0.00092[4] M☉
Radius	0.409±0.016[5] R☉
Luminosity	0.019[6] L☉
Temperature	3,353±60[5] K
Rotation	1.061 days[7]
B
Mass	0.16527±0.00025[4] M☉
Radius	0.303±0.013[5] R☉
Luminosity	0.008[6] L☉
Temperature	3,072±60[5] K
Rotation	0.404 days[7]
Other designations
EQ Peg, BD+19°5116, GJ 896, HIP 116132, WDS J23317+1956AB, G 68-24, G 129-19, G 128-71, LFT 1799, LHS 3965, LTT 16919, NLTT 57135[8]
EQ Peg A: TYC 1723-23-1, 2MASS J23315208+1956142[9]
EQ Peg B: LFT 1800, LHS 3966, LTT 16920, NLTT 57136, TYC 1723-23-2, 2MASS J23315244+1956138[9]
Database references
SIMBAD	The system
	A
	B
Exoplanet Archive	data

Discovery

EQ Pegasi was first noticed to be a binary star by Carl A. Wirtanen who in the course of a systematic survey of the McCormick Observatory photographic plates for M-type dwarfs, detected a companion about two magnitudes fainter at a separation of 3.5 arcseconds.^[11]

Both components were also thought to be single-lined spectroscopic binaries, with faint companions that have not been resolved in orbits of a few years,^[12][13] but this is no longer thought to be the case. A 2021 study of nearby stars states that "the spectroscopic binarity classification [...] is almost certainly due to activity".^[14]

Planetary system

In 2022, a Jovian planet was discovered in orbit around the system's primary star via radio astrometry. Along with the planet around TVLM 513-46546, this is the first confirmed exoplanet discovered entirely using astrometry.^[4]

The Gliese 896 A planetary system^[4]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	2.26±0.57 MJ	0.64282±0.00068	284.39±1.47	0.35±0.19	69.20±25.61°	—

In culture

In 1998, it was the basis of a hoax, as a telecommunications company claimed it had discovered "alien" signals originating from the star.^[15]

Gallery

• 
  A visual band light curve for EQ Pegasi A, adapted from Norton et al. (2007)^[16]
• 
  An ultraviolet band light curve for a flare on EQ Pegasi B, adapted from Mathioudakis et al. (2006)^[17]