Alpha Pavonis

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Alpha Pavonis
Diagram showing star positions and boundaries of the Pavo constellation and its surroundings
Cercle rouge 100%.svg

Location of α Pavonis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pavo
Right ascension 20h 25m 38.85705s[1]
Declination −56° 44′ 06.3230″[1]
Apparent magnitude (V) 1.94[2]
Spectral type B2 IV[3]
U−B color index −0.71[2]
B−V color index −0.20[2]
Radial velocity (Rv) +2.0[4] km/s
Proper motion (μ) RA: 6.90[1] mas/yr
Dec.: −86.02[1] mas/yr
Parallax (π) 18.24 ± 0.52[1] mas
Distance 179 ± 5 ly
(55 ± 2 pc)
Mass 6.3 ± 0.2[5] to 9.0 ± 0.1[6] M
Radius 4.5–5.6[7] R
Luminosity 2,200[5] L
Surface gravity (log g) 3.8[8] cgs
Temperature 18,000[8] K
Rotational velocity (v sin i) 39[8] km/s
Age 0.2[9] to 30[6] Myr
Other designations
Peacock, CD -57°9674, FK5 764, HD 193924, HIP 100751, HR 7790, SAO 246574.[3]
Database references

Alpha Pavonis (α Pavonis, abbreviated Alpha Pav, α Pav), also named Peacock,[10] is a binary star in the southern constellation of Pavo, near the shared border with the Telescopium constellation.


α Pavonis (Latinised to Alpha Pavonis) is the star's Bayer designation.

The historical name Peacock was assigned by Her Majesty's Nautical Almanac Office in the late 1930s during the creation of the Air Almanac, a navigational almanac for the Royal Air Force. Of the fifty-seven stars included in the new almanac, two had no classical names: Alpha Pavonis and Epsilon Carinae. The RAF insisted that all of the stars must have names, so new names were invented. Alpha Pavonis was named "Peacock" ('pavo' is Latin for 'peacock') whilst Epsilon Carinae was called "Avior".[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[13] included a table of the first two batches of names approved by the WGSN; which included Peacock for this star and Avior for Epsilon Carinae.


At an apparent magnitude of 1.94,[2] this is the brightest star in Pavo. Based upon parallax measurements, this star is about 179 light-years (55 parsecs) distant from the Earth.[1] It has an estimated six times the Sun's mass and 5–6 times the Sun's radius,[7] but 2,200 times the luminosity of the Sun.[5] However, Tetzlaff et al. (2011) suggest a much higher mass of 9 times the mass of the Sun.[9] The effective temperature of the photosphere is 18,000 K,[8] which gives the star a blue-white hue.[14] A stellar classification of B2 IV suggests it is a subgiant star that has begun to evolve from the main sequence with the exhaustion of the hydrogen at its core.

Stars with the mass of Alpha Pavonis are believed not to have a convection zone near their surface. Hence the material found in the outer atmosphere is not processed by the nuclear fusion occurring at the core. This means that the surface abundance of elements should be representative of the material out of which it originally formed. In particular, the surface abundance of deuterium should not change during the star's main sequence lifetime. The measured ratio of deuterium to hydrogen in this star amounts to less than 5 × 10−6, which suggests this star may have formed in a region with an unusually low abundance of deuterium, or else the deuterium was consumed by some means. A possible scenario for the latter is that the deuterium was burned through while Alpha Pavonis was a pre-main-sequence star.[8]

Alpha Pavonis is a spectroscopic binary consisting of a pair of stars that orbit around each other with a period of 11.753 days.[8] However, in part because the two stars have not been individually resolved, little is known about the companion.

The system may be a member of the Tucana-Horologium association of stars that share a common motion through space.[6] The estimated age of this association is 30 million years, which, as the members share a common origin, suggests a similar age for Alpha Pavonis.[15] However, Tetzlaff et al. (2011) suggest an age for this star of only 200,000 years. This star has a peculiar velocity of 13 km s−1 relative to its neighbors.[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 d Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N 
  3. ^ a b "PEACOCK -- Spectroscopic binary", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-23 
  4. ^ Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington, Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W 
  5. ^ a b c Jerzykiewicz, M.; Molenda-Zakowicz, J. (September 2000), "Empirical Luminosities and Radii of Early-Type Stars after Hipparcos", Acta Astronomica, 50: 369–380, Bibcode:2000AcA....50..369J 
  6. ^ a b c Zuckerman, B.; Song, Inseok; Webb, R. A. (September 2001), "Tucana Association", The Astrophysical Journal, 559 (1): 388–394, Bibcode:2001ApJ...559..388Z, doi:10.1086/322305 
  7. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics, 367 (2): 521–524, arXiv:astro-ph/0012289Freely accessible, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451 
  8. ^ a b c d e f Vidal-Madjar, A.; et al. (August 1988), "Deuterium in early-type stars - The case of Alpha-Pavonis", Astronomy and Astrophysics, 201 (2): 273–275, Bibcode:1988A&A...201..273V 
  9. ^ a b c Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  10. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  11. ^ Sadler, D. H. (1993), A Personal History of H.M. Nautical Almanac Office (PDF), Edited and privately published by Wilkins, G. A., p. 48 
  12. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  13. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  14. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  15. ^ da Silva, L.; et al. (December 2009), "Search for associations containing young stars (SACY). III. Ages and Li abundances", Astronomy and Astrophysics, 508 (2): 833–839, arXiv:0909.0677Freely accessible, Bibcode:2009A&A...508..833D, doi:10.1051/0004-6361/200911736