Sigma Scorpii

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Sigma Scorpii
Diagram showing star positions and boundaries of the Scorpius constellation and its surroundings
Cercle rouge 100%.svg
Location of σ Scorpii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Scorpius
Right ascension  16h 21m 11.31571s[1]
Declination –25° 35′ 34.0515″[1]
Apparent magnitude (V) +2.88[2]
Characteristics
Spectral type B1 III[3] + B1 V[4]
U−B color index –0.70[2]
B−V color index +0.13[2]
Astrometry
Radial velocity (Rv)–0.4[5] km/s
Proper motion (μ) RA: –10.60[1] mas/yr
Dec.: –16.28[1] mas/yr
Distance568+75
−59
 ly
(174+23
−18
[4] pc)
Absolute magnitude (MV)−4.12±0.34 / −3.32±0.34[4]
Orbit[4]
Primaryσ Sco Aa1
Companionσ Sco Aa2
Period (P)33.010±0.002 days
Semi-major axis (a)3.62±0.06 mas
Eccentricity (e)0.3220±0.0012
Inclination (i)158.2±2.3°
Longitude of the node (Ω)104±5°
Periastron epoch (T)34889.0±1.0 MJD
Argument of periastron (ω)
(secondary)
283±5°
Details
σ Sco Aa1
Mass18.4±5.4,[4] 17.2-18.0[6] M
Radius12.7±1.8[4] R
Luminosity(2.9±0.8)×104,[4] 95500[6] L
Surface gravity (log g)3.85[4] cgs
Temperature26150±1070,[4]27700[6] K
Metallicity [Fe/H]−0.20±0.20[7] dex
Rotational velocity (v sin i)25[8] km/s
Age8.0±0.2,[9] 8-10[6] Myr
σ Sco Aa2
Mass11.9±3.1[4] M
Radius11[4] R
Luminosity(1.6±0.4)×104[4] L
Other designations
Alniyat, Al Niyat, Pekehāwani, 20 Scorpii, ADS 10009, CD-25 11485, FK5 607, HD 147165, HIP 80112, HR 6084, SAO 184336, WDS 16212-2536.[10]
Database references
SIMBADdata

Sigma Scorpii (or σ Scorpii and abbreviated Sigma Sco, σ Sco), is a multiple star system in the constellation of Scorpius, located near the red supergiant Antares, which outshines it. This system has a combined apparent visual magnitude of +2.88,[2] making it one of the brighter members of the constellation. Based upon parallax measurements made during the Hipparcos mission, the distance to Sigma Scorpii is roughly 696 light-years (214 parsecs).[1] North et al. (2007) computed a more accurate estimate of 568+75
−59
 light years (174+23
−18
 parsecs).[4]

The system consists of a spectroscopic binary with components designated Sigma Scorpii Aa1 (also named Alniyat[11] and a Beta Cephei variable) and Aa2; a third component (designated Sigma Scorpii Ab) at 0.4 arcseconds from the spectroscopic pair, and a fourth component (Sigma Scorpii B) at about 20 arcseconds.[12]

Nomenclature[edit]

The red at bottom right is light from Sigma Scorpii being reflected off the surrounding dust.

σ Scorpii (Latinised to Sigma Scorpii) is the star system's Bayer designation. The designations of the four components as Sigma Scorpii Aa1, Aa2, Ab and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]

Sigma Scorpii and Tau Scorpii together bore the traditional name Al Niyat (or Alniyat) derived from the Arabic النياط an-niyāţ meaning "the arteries (of the scorpion)" and referring to their position flanking the star Antares, the scorpion's heart.[14] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[16] It approved the name Alniyat for the component Sigma Scorpii Aa1 on February 1, 2017 and it is now so included in the List of IAU-approved Star Names.[11]

In Chinese, 心宿 (Xīn Xiù), meaning Heart, refers to an asterism consisting of Sigma Scorpii, Antares and Tau Scorpii.[17] Consequently, Sigma Scorpii itself is known as 心宿一 (Xīn Xiù yī), "the First Star of Heart".[18]

The indigenous Boorong people of northwestern Victoria in Australia saw this star and Tau Scorpii as wives of Djuit (Antares).[19]

Properties[edit]

The brightest component of the system, Sigma Scorpii Aa, is a double-lined spectroscopic binary, which means that the pair has not been resolved using a telescope. Instead, their orbit is determined by changes in their combined spectrum caused by the Doppler shift. This indicates that the pair complete an orbit every 33.01 days and have an orbital eccentricity of 0.32.[4]

The primary component of the spectroscopic binary, Sigma Scorpii Aa1, is an evolved giant star with a stellar classification of B1 III.[3] It has around 18 times the mass of the Sun and 12 times the Sun's radius.[4] This star is radiating about 29000 times the luminosity of the Sun from its outer envelope at an effective temperature of 26150 K.[4] This is a variable star of the Beta Cephei type, causing the apparent magnitude to vary between +2.86 and +2.94 with multiple periods of 0.2468429, 0.239671, and 8.2 days. During each pulsation cycle, the temperature of the star varies by 4000±2000 K.[4] The other member of the core pair, Sigma Scorpii Aa2, is a main sequence star with a classification of B1 V.[4]

Orbiting this binary at a separation of half an arcsecond, or at least 120 Astronomical units (AU), four times the SunNeptune distance, is the magnitude +5.2 Sigma Scorpii Ab, which has an orbital period of over a hundred years. Even farther out at 20 arcseconds, or more than 4500 AU, is Sigma Scorpii B with a magnitude of +8.7. It is classified as a B9 dwarf.

Given its position, youth, and space velocity, the Sigma Scorpii system is a likely member of the Gould Belt,[20] and in particular the Upper Scorpius subgroup of the Scorpius-Centaurus Association (Sco OB2). Recent isochronal age estimates for the system yield ages of 8–10 million years through comparison of the HR diagram positions for the stars to modern evolutionary tracks.[4][6] This agrees well with the mean age for the Upper Scorpius group which is approximately 11 million years.[6]

References[edit]

  1. ^ a b c d e 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. ^ a b c d Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J.
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H
  4. ^ a b c d e f g h i j k l m n o p q r s North, J. R.; et al. (September 2007), "Orbital solution and fundamental parameters of σ Scorpii", Monthly Notices of the Royal Astronomical Society, 380 (3): 1276–1284, arXiv:0707.0897, Bibcode:2007MNRAS.380.1276N, doi:10.1111/j.1365-2966.2007.12188.x
  5. ^ Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington D.C. Bibcode:1953GCRV..C......0W.
  6. ^ a b c d e f Mark J. Pecaut; Eric E. Mamajek & Eric J. Bubar (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association". Astrophysical Journal. 746 (2): 154. arXiv:1112.1695. Bibcode:2012ApJ...746..154P. doi:10.1088/0004-637X/746/2/154.
  7. ^ Niemczura, E.; Daszyńska-Daszkiewicz, J. (April 2005), "Metallicities of the β Cephei stars from low-resolution ultraviolet spectra", Astronomy and Astrophysics, 433 (2): 659–669, arXiv:astro-ph/0410440, Bibcode:2005A&A...433..659N, doi:10.1051/0004-6361:20040396. Note: value taken from [m/H].
  8. ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  9. ^ 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
  10. ^ "sig Sco". SIMBAD. Centre de données astronomiques de Strasbourg.
  11. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  12. ^ "Washington Double Star Catalog". United States Naval Observatory. Archived from the original on 14 February 2011. Retrieved 2 January 2018.
  13. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  14. ^ Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 371. ISBN 0-486-21079-0.
  15. ^ "International Astronomical Union | IAU". www.iau.org. Retrieved 2017-03-31.
  16. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  17. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  18. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  19. ^ Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae" (PDF). Journal of Astronomical History & Heritage. 13 (3): 220–34. arXiv:1010.4610. Bibcode:2010JAHH...13..220H.
  20. ^ Bobylev, V. V.; Bajkova, A. T. (September 2007), "Kinematics of the Scorpius-Centaurus OB association", Astronomy Letters, 33 (9): 571–583, arXiv:0708.0943, Bibcode:2007AstL...33..571B, doi:10.1134/S1063773707090010