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Epoch J2000 Equinox J2000
|Right ascension||21h 14m 28.815s|
|Declination||+10° 00′ 25.13″|
|Apparent magnitude (V)||4.49 / 5.4|
|Spectral type||F5V+ / G0|
|U−B color index||−0.01|
|B−V color index||0.5|
|Radial velocity (Rv)||–15.4 km/s|
|Proper motion (μ)||RA: 42.39 ± 0.68 mas/yr
Dec.: –304.19 ± 0.42 mas/yr
|Parallax (π)||54.39 ± 0.15 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"|
|Longitude of the node (Ω)||23°|
|Periastron epoch (T)||1912.77|
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, with components of class G0 and F5. 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. The luminosity of the larger star is calculated to be 2.23 solar, and the smaller to be 2.17.
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.
- van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv: . Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
- Muterspaugh, Matthew W.; et al. (2005). "PHASES High-Precision Differential Astrometry of δ Equulei". The Astronomical Journal. 130 (6): 2866–2875. arXiv: . Bibcode:2005AJ....130.2866M. doi:10.1086/497035.
- "Delta Equulei". University of Illinois Astronomy department.
- 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.