4 Aquarii

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4 Aquarii
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension  20h 51m 25.74827s[1]
Declination −05° 37′ 35.8719″[1]
Apparent magnitude (V) 5.99[2] (6.40 + 7.43)[3]
Spectral type F7 IV + F6: V:[4]
B−V color index 0.464±0.003[2]
Radial velocity (Rv)−21.50[5] km/s
Proper motion (μ) RA: 95.47[1] mas/yr
Dec.: 1.78[1] mas/yr
Parallax (π)16.47 ± 0.59[1] mas
Distance198 ± 7 ly
(61 ± 2 pc)
Absolute magnitude (MV)2.15[6]
Period (P)200.7±1.1 yr
Semi-major axis (a)0.816±0.006
Eccentricity (e)0.535+0.006
Inclination (i)64.06+0.26
Longitude of the node (Ω)174.31+0.38
Periastron epoch (T)B 1,896.8+0.39
Argument of periastron (ω)
4 Aqr A
Mass1.618±0.004[7] M
Luminosity11.0 L
Surface gravity (log g)3.79 cgs
Temperature6,440 K
Metallicity [Fe/H]0.18[8] dex
Rotational velocity (v sin i)34.6 km/s
Age1.60[8] Gyr
4 Aqr B
Mass1.331±0.003[7] M
Other designations
4 Aqr, BD−06°5604, HD 198571, HIP 102945, HR 7982, SAO 144877, WDS J2051.4-0538[9]
Database references
4 Aqr A
4 Aqr B

4 Aquarii (abbreviated 4 Aqr) is a binary star system in the constellation Aquarius,[9] located approximately 198 light years away from the Sun.[1] 4 Aquarii is the Flamsteed designation. It is visible to the naked eye as a dim, yellow-white hued star with a combined apparent visual magnitude of 5.99.[2] The system is moving closer to the Earth with a heliocentric radial velocity of −21.5 km/s.[5]

This is a visual binary with an orbital period of 200.7 years and an eccentricity of 0.535.[7] The magnitude 6.40[3] primary, designated component A, is an F-type subgiant star with a stellar classification of F7 IV,[4] suggesting that it has exhausted the hydrogen at its core and evolved off the main sequence.[7] It has a dynamically-measured mass 1.6[7] times that of the Sun and is radiating 11 times the Sun's luminosity from its photosphere at an effective temperature of 6,440 K.[6] The magnitude 7.43[3] secondary, component B, is a suspected F-type main-sequence star of class F6 V.[4] The pair are an estimated 1.6 billion years old.[8]


  1. ^ a b c d e f 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.
  2. ^ a b c 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.
  3. ^ a b c Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
  4. ^ a b c Corbally, C. J.; Garrison, R. F. (August 1980). "New spectral classifications on the MK system for visual double stars". Publications of the Astronomical Society of the Pacific. 92: 493–496. Bibcode:1980PASP...92..493C. doi:10.1086/130700.
  5. ^ a b Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  6. ^ a b c Luck, R. Earle (January 2017). "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants". The Astronomical Journal. 153 (1): 19. arXiv:1611.02897. Bibcode:2017AJ....153...21L. doi:10.3847/1538-3881/153/1/21. 21.
  7. ^ a b c d e f Mendez, Rene A.; et al. (November 2017). "Orbits for 18 Visual Binaries and Two Double-line Spectroscopic Binaries Observed with HRCAM on the CTIO SOAR 4 m Telescope, Using a New Bayesian Orbit Code Based on Markov Chain Monte Carlo". The Astronomical Journal. 154 (5): 22. arXiv:1709.06582. Bibcode:2017AJ....154..187M. doi:10.3847/1538-3881/aa8d6f. 187.
  8. ^ a b c Casagrande, L.; et al. (June 2011). "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey". Astronomy and Astrophysics. 530: A138. arXiv:1103.4651. Bibcode:2011A&A...530A.138C. doi:10.1051/0004-6361/201016276.
  9. ^ a b "* 4 Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 23 October 2014.