Sigma Scorpii

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"Al Niyat" redirects here. For the other star that traditionally bore this name, see Tau Scorpii.
Sigma Scorpii
Location of σ Scorpii (circled)
Observation data
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]
Distance
568+75
−59 ly
(174+23
−18[4] pc)
Absolute magnitude (MV)−4.12±0.34 / −3.32±0.34[4]
Argument of periastron
(ω)
(secondary)		283±5°
Details
σ Sco Aa1
Myr
σ Sco Aa2
Mass11.9±3.1[4] M☉
Radius11[4] R☉
Luminosity16000±4000[4] L☉
FK5 607, HD 147165, HIP 80112, HR 6084, SAO 184336, WDS 16212-2536.[10]
Database references
SIMBADdata

Sigma Scorpii (or σ Scorpii, abbreviated Sigma Sco or σ Sco), is a

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

arcseconds from the spectroscopic pair, and a fourth component (Sigma Scorpii B) at about 20 arcseconds.[13]

Nomenclature

Rho Ophiuchi cloud complex in the infrared: the "red" at bottom right is 22-micron infrared light from Sigma Scorpii being reflected off the surrounding dust (Sh2-9).

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).[14]

Sigma Scorpii and Tau Scorpii together bore the traditional name Al Niyat (or Alniyat) derived from the Arabic النياط al-niyāţ "the arteries" and referring to their position flanking the star Antares, the scorpion's heart, with Sigma Scorpii just to the north.[15]

In 2016, the

multiple systems.[17] 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.[12]

In

Chinese name for Sigma Scorpii itself is 心宿一 (Xīn Xiù yī), "the First Star of Heart".[19]

The indigenous

Victoria in Australia saw this star and Tau Scorpii as wives of Djuit (Antares).[20]

Properties

A light curve for Sigma Scorpii, plotted from Hipparcos data[21]

The brightest component of the system, Sigma Scorpii Aa, is a double-lined

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 Sun–Neptune 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

evolutionary tracks.[4][6] This agrees well with the mean age for the Upper Scorpius group which is approximately 11 million years.[6]

References

  1. ^
    S2CID 18759600
    .
  2. ^
    Bibcode:1966CoLPL...4...99J
    .
  3. ^
    Bibcode:1988mcts.book.....H
  4. ^
    S2CID 14636283
  5. Bibcode:1953GCRV..C......0W
    .
  6. ^
    S2CID 118461108
    .
  7. S2CID 14295631
    . Note: value taken from [m/H].
  8. doi:10.1086/340590
  9. S2CID 118629873
  10. ^ "sig Sco". SIMBAD. Centre de données astronomiques de Strasbourg.
  11. ISBN 978-1-931559-44-7
    .
  12. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  13. ^ "Washington Double Star Catalog". United States Naval Observatory. Archived from the original on 14 February 2011. Retrieved 2 January 2018.
  14. arXiv:1012.0707 [astro-ph.SR
    ].
  15. ISBN 0-486-21079-0
    .
  16. ^ "International Astronomical Union | IAU". www.iau.org. Retrieved 2017-03-31.
  17. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  18. ISBN 978-986-7332-25-7
    .
  19. ^ (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.
  20. S2CID 118454721
    .
  21. ^ "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
  22. S2CID 15785349
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