Delta Equulei

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Delta Equulei
Observation data
Epoch J2000      Equinox J2000
Constellation Equuleus
Right ascension 21h 14m 28.815s[1]
Declination +10° 00′ 25.13″[1]
Apparent magnitude (V) 4.49 / 5.4
Spectral type F5V+ / G0
U−B color index −0.01
B−V color index 0.5
Variable type None
Radial velocity (Rv) –15.4 km/s
Proper motion (μ) RA: 42.39 ± 0.68[1] mas/yr
Dec.: –304.19 ± 0.42[1] mas/yr
Parallax (π) 54.39 ± 0.15[2] mas
Distance 60.0 ± 0.2 ly
(18.39 ± 0.05 pc)
Absolute magnitude (MV) 4.99
Mass 1.22 / 1.17 M
Radius 1.19 / 0.525 R
Luminosity 2.23 / 2.17 L
Age 1.6 – 2.8 billion years
Companion Delta Equulei B
Period (P) 5.7 yr
Semi-major axis (a) 0.26"
Eccentricity (e) 0.42
Inclination (i) 100°
Longitude of the node (Ω) 23°
Periastron epoch (T) 1912.77
Other designations
del Equ, 7 Equ, HD 202275, LTT 16227, GJ 822.0, HIP 104858, BD+09°4746, HR 8123, SAO 126643
Database references

Delta Equulei (δ Equulei, δ Equ) is the second brightest star in the constellation Equuleus. Delta Equulei is a binary star system about 60 light years away,[2] with components of class G0 and F5.[3] 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.[3] The luminosity of the larger star is calculated to be 2.23 solar, and the smaller to be 2.17.[3]


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.[4]


  1. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.  Vizier catalog entry
  2. ^ a b Muterspaugh, Matthew W.; et al. (2005). "PHASES High-Precision Differential Astrometry of δ Equulei". The Astronomical Journal. 130 (6): 2866–2875. arXiv:astro-ph/0507585Freely accessible. Bibcode:2005AJ....130.2866M. doi:10.1086/497035. 
  3. ^ a b c "Delta Equulei". University of Illinois Astronomy department. 
  4. ^ Struve, Otto Wilhelm (1859). "On some lately discovered Double Stars" (PDF). Monthly Notices of the Royal Astronomical Society. 20: 8. Bibcode:1859MNRAS..20....8S. doi:10.1093/mnras/20.1.8. 

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