Alpha Pavonis

Alpha Pavonis (α Pavonis, abbreviated Alpha Pav, α Pav), formally named Peacock /ˈpiːkɒk/, is a binary star in the southern constellation of Pavo, near the border with the constellation Telescopium.

α Pavonis
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]
Characteristics
Spectral type B3 V[3]
U−B color index −0.71[2]
B−V color index −0.20[2]
Astrometry
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
Distance179 ± 5 ly
(55 ± 2 pc)
Absolute magnitude (MV)−1.762[5]
Details
Mass5.91[6] M☉
Radius4.83[7] R☉
Luminosity2,200[7] L☉
Surface gravity (log g)3.94[6] cgs
Temperature17,711[6] K
Rotational velocity (v sin i)16[6] km/s
Age48[6] Myr
Other designations
Peacock, CD-57° 9674, FK5 764, HD 193924, HIP 100751, HR 7790, SAO 246574.[8]
Database references
SIMBADdata

Nomenclature

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".[9] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[11] 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.[12]

In Chinese caused by adaptation of the European southern hemisphere constellations into the Chinese system, 孔雀 (Kǒng Qiāo), meaning Peacock, refers to an asterism consisting of α Pavonis, η Pavonis, π Pavonis, ν Pavonis, λ Pavonis, κ Pavonis, δ Pavonis, β Pavonis, ζ Pavonis, ε Pavonis and γ Pavonis. Consequently, α Pavonis itself is known as 孔雀十一 (Kǒng Qiāo shíyī, English: the Eleventh Star of Peacock.)[13]

Properties

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 6 times the Sun's radius, but 2,200 times the luminosity of the Sun.[7] The effective temperature of the photosphere is 17,700 K, which gives the star a blue-white hue.[14] It has a stellar classification of B3 V,[3] although older studies have often given it a subgiant luminosity class.[15] It is classified as B2.5 IV in the Bright Star Catalogue.[16]

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.[17]

The system is likely to be a member of the Tucana-Horologium association that share a common motion through space.[5] The estimated age of this association is 45 million years.[5] α Pavonis star has a peculiar velocity of 13 km s−1 relative to its neighbors.[18]

Companions

Three stars have been listed as visual companions to α Pavonis: two ninth magnitude stars at about four arc minutes; and a 12th magnitude F5 main sequence star at about one arc minute.[19][3] The two ninth magnitude companions are only 17 arc seconds from each other.[19]

α Pavonis A is a spectroscopic binary consisting of a pair of stars that orbit around each other with a period of 11.753 days.[17] However, in part because the two stars have not been individually resolved, little is known about the companion except that it has a mass of at least 0.26 M☉.[20] One attempt to model a composite spectrum estimated components with spectral types of B0.5 and B2, and a brightness difference between the two components of 1.3 magnitudes.[21]

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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.
  2. 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. Gahm, G. F.; Ahlin, P.; Lindroos, K. P. (1983). "A study of visual double stars with early type primaries. I - Spectroscopic results". Astronomy and Astrophysics Supplement Series. 51: 143. Bibcode:1983A&AS...51..143G.
  4. Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington, Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W
  5. Bell, Cameron P. M.; Mamajek, Eric E.; Naylor, Tim (2015). "A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood". Monthly Notices of the Royal Astronomical Society. 454: 593. arXiv:1508.05955. Bibcode:2015MNRAS.454..593B. doi:10.1093/mnras/stv1981.
  6. David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146.
  7. 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
  8. "PEACOCK -- Spectroscopic binary", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-23
  9. Sadler, D. H. (1993), A Personal History of H.M. Nautical Almanac Office (PDF), Edited and privately published by Wilkins, G. A., p. 48
  10. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  11. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  12. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  13. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 30 日
  14. "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
  15. Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)". VizieR On-line Data Catalog: B/mk. Originally Published in: Lowell Observatory (October 2014). 1. Bibcode:2014yCat....1.2023S.
  16. Hoffleit, D.; Jaschek, C. (1991). The Bright star catalogue. New Haven: Yale University Observatory. Bibcode:1991bsc..book.....H.
  17. 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
  18. 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:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x
  19. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  20. Bonavita, M.; Desidera, S.; Thalmann, C.; Janson, M.; Vigan, A.; Chauvin, G.; Lannier, J. (2016). "SPOTS: The Search for Planets Orbiting Two Stars. II. First constraints on the frequency of sub-stellar companions on wide circumbinary orbits". Astronomy & Astrophysics. 593: A38. arXiv:1605.03962. Bibcode:2016A&A...593A..38B. doi:10.1051/0004-6361/201628231.
  21. Beavers, W. I.; Cook, D. B. (1980). "Scanner studies of composite spectra. I - Dwarfs". Astrophysical Journal Supplement Series. 44: 489. Bibcode:1980ApJS...44..489B. doi:10.1086/190702.


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