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.^[11] 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	0.35[5] R☉
Luminosity	0.019[6] L☉
Temperature	3,585[7] K
Rotation	1.061 days[5]
B
Mass	0.16527±0.00025[4] M☉
Radius	0.25[5] R☉
Luminosity	0.008[6] L☉
Temperature	3,309[8] K
Rotation	0.404 days[5]
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[9]
EQ Peg A: TYC 1723-23-1, 2MASS J23315208+1956142[10]
EQ Peg B: LFT 1800, LHS 3966, LTT 16920, NLTT 57136, TYC 1723-23-2, 2MASS J23315244+1956138[10]
Database references
SIMBAD	The system
	A
	B

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.^[12]

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,^[13][14] 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".^[15]

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.^[16]

Gallery

• 
  A visual band light curve for EQ Pegasi A, adapted from Norton et al. (2007)^[17]
• 
  An ultraviolet band light curve for a flare on EQ Pegasi B, adapted from Mathioudakis et al. (2006)^[18]

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
3. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
4. Curiel, Salvador; Ortiz-León, Gisela N.; Mioduszewski, Amy J.; Sanchez-Bermudez, Joel (September 2022). "3D Orbital Architecture of a Dwarf Binary System and Its Planetary Companion". The Astronomical Journal. 164 (3): 93. arXiv:2208.14553. Bibcode:2022AJ....164...93C. doi:10.3847/1538-3881/ac7c66. S2CID 251953478.
5. Morin, J.; Donati, J.-F.; et al. (October 2008). "Large-scale magnetic topologies of mid M dwarfs". Monthly Notices of the Royal Astronomical Society. 390 (2): 567–581. arXiv:0808.1423. Bibcode:2008MNRAS.390..567M. doi:10.1111/j.1365-2966.2008.13809.x. S2CID 11240756.
6. Morales, J. C.; Ribas, I.; Jordi, C. (2008). "The effect of activity on stellar temperatures and radii". Astronomy and Astrophysics. 478 (2): 507. arXiv:0711.3523. Bibcode:2008A&A...478..507M. doi:10.1051/0004-6361:20078324. S2CID 16238033.
7. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
8. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
9. "BD+19 5116". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 18 August 2017.
10. "BD+19 5116A". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 18 August 2017.
11. Crosley, M. K.; Osten, R. A. (2018). "Constraining Stellar Coronal Mass Ejections through Multi-wavelength Analysis of the Active M Dwarf EQ Peg". The Astrophysical Journal. 856 (1). 39. arXiv:1802.03440. Bibcode:2018ApJ...856...39C. doi:10.3847/1538-4357/aaaec2. S2CID 55448675.
12. Wirtanen, C. A. (1941). "A New dMe Double Star". Publications of the Astronomical Society of the Pacific. 53 (316): 340. Bibcode:1941PASP...53..340W. doi:10.1086/125371.
13. Tokovinin, A. "Multiple Star Catalog". Retrieved 2019-08-12.
14. Delfosse, X.; Forveille, T.; et al. (April 1999). "New neighbours. I. 13 new companions to nearby M dwarfs". Astronomy and Astrophysics. 344: 897–910. arXiv:astro-ph/9812008. Bibcode:1999A&A...344..897D.
15. Reylé, Céline; Jardine, Kevin; Fouqué, Pascal; Caballero, Jose A.; Smart, Richard L.; Sozzetti, Alessandro (30 April 2021). "The 10 parsec sample in the Gaia era". Astronomy & Astrophysics. 650: A201. arXiv:2104.14972. Bibcode:2021A&A...650A.201R. doi:10.1051/0004-6361/202140985. S2CID 233476431. Data available at https://gruze.org/10pc/
16. "BBC News | Sci/Tech | Alien hoax dismays scientists". news.bbc.co.uk. Retrieved 2018-09-25.
17. Norton, A. J.; Wheatley, P. J.; West, R. G.; Haswell, C. A.; Street, R. A.; Collier Cameron, A.; Christian, D. J.; Clarkson, W. I.; Enoch, B.; Gallaway, M.; Hellier, C.; Horne, K.; Irwin, J.; Kane, S. R.; Lister, T. A.; Nicholas, J. P.; Parley, N.; Pollacco, D.; Ryans, R.; Skillen, I.; WilsonD. M. (May 2007). "New periodic variable stars coincident with ROSAT sources discovered using SuperWASP". Astronomy and Astrophysics. 467 (2): 785–905. arXiv:astro-ph/0702631. Bibcode:2007A&A...467..785N. doi:10.1051/0004-6361:20077084. S2CID 16358048. Retrieved 11 February 2022.
18. Mathioudakis, M.; Bloomfield, D. S.; Jess, D. B.; Dhillon, V. S.; Marsh, T. R. (September 2006). "The periodic variations of a white-light flare observed with ULTRACAM". Astronomy and Astrophysics. 456 (1): 323–327. arXiv:astro-ph/0605196. Bibcode:2006A&A...456..323M. doi:10.1051/0004-6361:20054752. S2CID 8572363. Retrieved 12 February 2022.