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Delta Equulei
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Equuleus
Right ascension	21h 14m 28.81531s
Declination	+10° 00′ 25.1259″
Apparent magnitude (V)	5.19 + 5.52
Characteristics
Spectral type	F7V + F7V
U−B color index	−0.03
B−V color index	+0.49
Astrometry
Radial velocity (Rv)	−16.2±0.3 km/s
Proper motion (μ)	RA: +42.39 mas/yr ; Dec.: −304.19 mas/yr
Parallax (π)	54.89 ± 0.50 mas
Distance	59.4 ± 0.5 ly ; (18.2 ± 0.2 pc)
Absolute magnitude (MV)	+3.14
Orbit
Period (P)	2,084.03±0.10 d
Semi-major axis (a)	231.9650±0.0080 mas
Eccentricity (e)	0.436851±0.000025
Inclination (i)	99.4083±0.0098°
Longitude of the node (Ω)	23.362±0.012°
Periastron epoch (T)	53112.071±0.052 MHJD
Argument of periastron (ω); (secondary)	7.735±0.013°
Details
δ Equ A
Mass	1.192±0.012 M☉
Radius	1.30±0.08 R☉
Luminosity	2.25 L☉
Temperature	6,200±150 K
Metallicity [Fe/H]	−0.07±0.09 dex
Age	3.0 Gyr
δ Equ B
Mass	1.187±0.012 M☉
Radius	1.25±0.08 R☉
Luminosity	2.07 L☉
Temperature	6,200±150 K
Other designations
	δ Equ, 7 Equulei, BD+09° 4746, GJ 822.0, HD 202275, HIP 104858, HR 8123, LTT 16227, SAO 126643.
Database references
SIMBAD	data

Delta Equulei, Latinized from δ Equulei, is the second brightest star in the constellation Equuleus. Delta Equulei is a binary star system about 60 light years away,^[9] with components of class G0 and F5.^[10] Their combined magnitude is 4.47, and their absolute magnitude is 3.142. There is controversy as to the exact masses of the stars. One study puts the larger at 1.22 solar masses and the smaller at 1.17, while another pegs them at 1.66 and 1.593.^[10] The luminosity of the larger star is calculated to be 2.23 solar, and the smaller to be 2.17.^[10]

System

William Herschel listed Delta Equulei as a wide binary. Friedrich Georg Wilhelm von Struve later showed this to be an unrelated optical double star. However his son Otto Wilhelm von Struve while making follow-up observations in 1852 found that while the separation of the optical double continued to increase, Delta Equulei itself appeared elongated. He concluded that it is a much more compact binary.^[11]

References

^ ^a ^b ^c ^d ^e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
^ Malkov, O. Yu.; et al. (2012), "Dynamical Masses of a Selected Sample of Orbital Binaries", Astronomy & Astrophysics, 546: 5, Bibcode:2012A&A...546A..69M, doi:10.1051/0004-6361/201219774, A69
^ ^a ^b ^c ^d ^e ^f ^g Torres, G.; et al. (February 2010), "Accurate masses and radii of normal stars: modern results and applications", The Astronomy and Astrophysics Review, 18 (1–2): 67–126, arXiv:0908.2624, Bibcode:2010A&ARv..18...67T, doi:10.1007/s00159-009-0025-1, S2CID 14006009.
^ ^a ^b Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, Bibcode:1986EgUBV........0M.
^ ^a ^b Casagrande, L.; et al. (2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy & Astrophysics, 530 (A138): 21, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276, S2CID 56118016.
^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
^ ^a ^b ^c Muterspaugh, Matthew W.; et al. (March 2008), "Masses, Luminosities, and Orbital Coplanarities of the μ Orionis Quadruple-Star System from Phases Differential Astrometry", The Astronomical Journal, 135 (3): 766–776, arXiv:0710.2126, Bibcode:2008AJ....135..766M, doi:10.1088/0004-6256/135/3/766, S2CID 6531922. See Table 5.
^ "del Equ". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-02-17.
^ Muterspaugh, Matthew W.; et al. (2005). "PHASES High-Precision Differential Astrometry of δ Equulei". The Astronomical Journal. 130 (6): 2866–2875. arXiv:astro-ph/0507585. Bibcode:2005AJ....130.2866M. doi:10.1086/497035. S2CID 12044718.
^ ^a ^b ^c "Delta Equulei". University of Illinois Astronomy department. Archived from the original on 2006-12-16.
^ Struve, Otto Wilhelm (1859). "On some lately discovered Double Stars" (PDF). Monthly Notices of the Royal Astronomical Society. 20: 8–13. Bibcode:1859MNRAS..20....8S. doi:10.1093/mnras/20.1.8.