25 Aquarii

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]

25 Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Location of 25 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]
Characteristics
Spectral type K0 III[3]
U−B color index +0.90[2]
B−V color index +1.032[4]
Astrometry
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 mas[1]
Distance226 ± 5 ly
(69 ± 1 pc)
Details
Radius11[4] R☉
Luminosity54[4] L☉
Surface gravity (log g)2.5[4] cgs
Temperature4,721[4] K
Metallicity [Fe/H]–0.17[4] dex
Rotational velocity (v sin i)2.5[4] km/s
Other designations
d  Aquarii, 25 Aqr, 6 Pegasi, BD+01 4517, FK5 3729, HD 206067, HIP 106944, HR 8277, SAO 126965[5]
Database references
SIMBADdata

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]

References
  1. van Leeuwen, F. (November 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.
  2. Argue, A. N. (1966), "UBV photometry of 550 F, G and K type stars", Monthly Notices of the Royal Astronomical Society, 133 (4): 475–493, Bibcode:1966MNRAS.133..475A, doi:10.1093/mnras/133.4.475.
  3. 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:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
  4. 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". SIMBAD. 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, S2CID 118445625.
  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/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272, S2CID 17804304.
  8. Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.
  9. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on February 22, 2012, retrieved 2012-01-16.
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