25 Aquarii

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25 Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of 88 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 21h 39m 33.26758s[1]
Declination +02° 14′ 36.8173″[1]
Apparent magnitude (V) +5.09[2]
Spectral type K0 III[3]
U−B color index +0.90[2]
B−V color index +1.032[4]
Radial velocity (Rv) –34.63 ± 0.11[4] km/s
Proper motion (μ) RA: –29.55[1] mas/yr
Dec.: –83.22[1] mas/yr
Parallax (π) 14.40 ± 0.30[1] mas
Distance 226 ± 5 ly
(69 ± 1 pc)
Radius 11[4] R
Luminosity 54[4] L
Surface gravity (log g) 2.5[4] cgs
Temperature 4,721[4] K
Metallicity [Fe/H] –0.17[4] dex
Rotational velocity (v sin i) 2.5[4] km/s
Other designations
BD+01 4517, FK5 3729, HD 206067, HIP 106944, HR 8277, SAO 126965.[5]
Database references

25 Aquarii (abbreviated 25 Aqr) is a single[3] star in the equatorial constellation of Aquarius. 25 Aquarii is the modern Flamsteed designation; in the past it held the designation 6 Pegasi.[6] It also bears the Bayer designation of d Aquarii. It is located near the border with the modern Pegasus constellation. Although faint at an apparent visual magnitude of +5.09,[2] it is bright enough to be viewed from suburban skies. Based upon an annual parallax shift of 0.01440 arcseconds,[1] it is located at a distance of around 226 light-years (69 parsecs) from Earth. The visual magnitude of the star is diminished by 0.09 from extinction caused by intervening gas and dust.[7]

The spectrum of this star matches a stellar classification of K0 III,[3] with the luminosity class of III indicating that this is a giant star that has evolved away from the main sequence after exhausting the supply of hydrogen at its core. It belongs to a population known as clump giants and hence is generating energy through the nuclear fusion of helium at the core.[8] The outer envelope has expanded to 11 times the radius of the Sun and it is radiating 54 times the Sun's luminosity.[4] This energy is being emitted from the stellar atmosphere at an effective temperature of 4,721 K,[4] causing it to glow with the orange hue of a K-type star.[9]


  1. ^ a b c d e f van Leeuwen, F. (November 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. 
  2. ^ a b c Argue, A. N. (1966), "UBV photometry of 550 F, G and K type stars", Monthly Notices of the Royal Astronomical Society, 133: 475–493, Bibcode:1966MNRAS.133..475A, doi:10.1093/mnras/133.4.475. 
  3. ^ a b c Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878Freely accessible. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. 
  4. ^ a b c d e f g h i j Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209. 
  5. ^ "d Aqr -- Star in double system", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-13. 
  6. ^ Wagman, M. (August 1987), "Flamsteed's Missing Stars", Journal for the History of Astronomy, 18 (3): 220, Bibcode:1987JHA....18..209W, doi:10.1177/002182868701800305. 
  7. ^ Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430: 165–186, arXiv:astro-ph/0409579Freely accessible, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272. 
  8. ^ Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329Freely accessible, Bibcode:2000ApJ...539..732A, doi:10.1086/309278. 
  9. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 10, 2012, retrieved 2012-01-16. 

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