Beta Scorpii

Beta Scorpii (β Scorpii, abbreviated Beta Sco, β Sco) is a multiple star system in the southern zodiac constellation of Scorpius. It bore the traditional proper name of Acrab /ˈækræb/,[8] though the International Astronomical Union now regards that name as applying only to the β Scorpii Aa component.

β Scorpii
Location of β Scorpii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Scorpius
HR 5984
Right ascension 16h 05m 26.23198s[1]
Declination –19° 48′ 19.6300″[1]
Apparent magnitude (V) 2.62[2]
HR 5985
Right ascension 16h 05m 26.57128s[1]
Declination –19° 48′ 06.8556″[1]
Apparent magnitude (V) 4.92[2]
Characteristics
HR 5984
Spectral type B1V[3] (B0.5IV-V + B1.5V)[4]
U−B color index –0.08[5]
B−V color index –0.08[5]
HR 5985
Spectral type B2V[3]
U−B color index –0.70[5]
B−V color index –0.02[5]
Astrometry
HR 5984
Radial velocity (Rv)–1.0[6] km/s
Proper motion (μ) RA: –5.20[1] mas/yr
Dec.: –24.04[1] mas/yr
Parallax (π)8.07 ± 0.78 mas[1]
Distance400 ± 40 ly
(120 ± 10 pc)
Absolute magnitude (MV)–3.92 / –2.60[7]
HR 5985
Radial velocity (Rv)–3.6[6] km/s
Proper motion (μ) RA: –5.07[1] mas/yr
Dec.: –25.87[1] mas/yr
Parallax (π)8.19 ± 1.17 mas[1]
Distanceapprox. 400 ly
(approx. 120 pc)
Absolute magnitude (MV)–1.83 (Ea: +0.24)[7]
Details[7]
β Sco Aa
Mass15.0 M☉
Radius6.3 R☉
Luminosity31,600 L☉
Temperature28,000 K
β Sco Ab
Mass10.4 M☉
Radius4.0 R☉
Luminosity7,900 L☉
Temperature26,400 K
β Sco C
Mass8.2 M☉
Radius2.9 R☉
Luminosity3,200 L☉
Surface gravity (log g)3.8 cgs
Temperature24,000 K
Rotational velocity (v sin i)55 km/s
β Sco Ea
Mass3.5 M☉
Radius2.4 R☉
Luminosity126 L☉
Surface gravity (log g)4.2 cgs
Temperature13,000 K
Rotational velocity (v sin i)5 km/s
Age6.3 Myr
Other designations
Acrab, Elacrab, Graffias, 8 Scorpii, ADS 9913, WDS J16054-1948
β1 Sco: BD–19 4307, HD 144217, HIP 78820, HR 5984
β2 Sco: BD–19 4308, HD 144218, HIP 78821, HR 5985
Database references
SIMBADβ Scorpii
β1 Scorpii
β2 Scorpii

Components

Observed through a small telescope, Beta Scorpii appears as a binary star with a separation between the two components of 13.5 arcseconds and a combined apparent magnitude of 2.50. This pair, designated β¹ Scorpii and β² Scorpii, form the top branches of a hierarchy of six orbiting components.

Aa
Period = 6.82d
a = 1.42 mas
Ab
Period = 610y
a = 0.30″
B
13.5″ separation
C
Period = 39y
a = 0.1328″
Ea
Period = 10.7d
Eb

Hierarchy of orbits in the β Scorpii system

β¹ Scorpii, the brighter of the pair, consists of two sub-components, designated β Scorpii A and β Scorpii B, orbiting at an angular separation of 0.3 arcseconds with an orbital period of 610 years. β Scorpii A is itself a spectroscopic binary, with the two components designated β Scorpii Aa (also named Acrab[9]) and β Scorpii Ab. They are separated by 1.42 milliarcseconds and have an orbital period of 6.82 days.[10]

β² Scorpii also has two sub-components, designated β Scorpii C and β Scorpii E, orbiting at an angular separation of 0.1328 arcseconds with an orbital period of 39 years. β Scorpii E in turn is a spectroscopic binary with components designated β Scorpii Ea and β Scorpii Eb and having an orbital period of 10.7 days.

Component β Scorpii D is the unrelated seventh magnitude star HD 144273, 520" away.[11] Some authors have also referred to component Ab as D.[12]

A companion to component B, β Scorpii G, has been proposed to account for missing mass in the system, but no further evidence of its existence has been found.[7] β Scorpii F refers to a theorised companion to component E.[12]

Nomenclature

β Scorpii (Latinised to Beta Scorpii) is the star's Bayer designation; β¹ and β² Scorpii, those of its two components. The designations of the sub-components - β Scorpii A, Aa, Ab, B, C, E, Ea and Eb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]

Beta Scorpii bore the traditional names Acrab, Akrab or Elacrab, all deriving from the Arabic name (Arabic: العقرب) al-'Aqrab 'the Scorpion' for the whole constellation, as well as Graffias /ˈɡræfiəs/,[14] Italian for "the claws", a name it shared with Xi Scorpii.[15][16]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[17] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[18] It approved the name Acrab for the component β Scorpii Aa on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[9]

In Chinese, 房宿 (Fáng Xiù), meaning Room, refers to an asterism consisting of both of β1 Scorpii and β2 Scorpii, π Scorpii, ρ Scorpii and δ Scorpii, .[19] Consequently, the Chinese name for both of β1 Scorpii and β2 Scorpii is 房宿四 (Fáng Xiù sì), "the Fourth Star of Room".[20]

Namesake

USS Graffias (AF-29) was once a United States navy ship named after the star.

Properties
Image of Scorpius and the Milky Way with β Scorpii in the top right corner

The β Scorpii system is a kinematic member of the Upper Scorpius subgroup of the Scorpius–Centaurus association, a group of thousands of young stars with mean age 11 million years at distance 470 light years (145 parsecs). Analysis of β1 Scorpii as a single star derived an evolutionary age between 9 and 12 million years,[21] but analysis of the β Scorpii system as a whole suggest an age closer to 6 million years.[7]

The two components of β Scorpii A are the most massive members of the system, 15 M☉ and 10 M☉ respectively. The combined spectral type is B1 V. The individual spectral types cannot be clearly measured, but are estimated to be B0.5 and B1.5. Component Aa is evolving slightly away from the zero age main sequence and its luminosity class is estimated to be intermediate between subgiant (IV) and main sequence (V). Component Ab has a main sequence luminosity class, a temperature of 26,400 K, and a luminosity of 7,900 L☉.

Component B is over 20 times fainter than the combined component A stars and a clear spectral type has not been measured. Its mass is estimated to be approximately 8 M☉.[12]

Component C has a stellar classification of B2 V and a mass of 8 M☉. It has an effective surface temperature of 24,000 K, a radius of 2.9 R☉ and a bolometric luminosity of 3,200 L☉.

Component E is determined to have a temperature of 13,000 K, radius of 2.4 R☉, and luminosity of 126 L☉. It is chemically peculiar, with high abundances of manganese and strontium. It is possibly a mercury-manganese (HgMn) star, but abundances of other metals are unexpectedly low.[7]

Beta Scorpii is 1.01 degree from the ecliptic and can be occulted by the Moon and, very rarely, by planets. On December 9, 1906, it was occulted by Venus.[22] The last occultation by a planet took place on 13 May 1971, by Jupiter.[23]

In culture

Beta Scorpii appears on the flag of Brazil, symbolising the state of Maranhão.[24]

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. Hoffleit, D.; Warren Jr., W. H. (1991). "Entry for HR 2491". Bright Star Catalogue, 5th Revised Ed. (Preliminary Version). CDS. ID V/50.
  3. Abt, H. A. (1981). "Visual multiples. VII - MK classifications". Astrophysical Journal Supplement Series. 45: 437. Bibcode:1981ApJS...45..437A. doi:10.1086/190719.
  4. Holmgren, D.; Hadrava, P.; Harmanec, P.; Koubsky, P.; Kubat, J. (1997). "Search for forced oscillations in binaries. II. β Scorpii A. New physical parameters and a search for line profile variability". Astronomy and Astrophysics. 322: 565. Bibcode:1997A&A...322..565H.
  5. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
  6. Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications. IAU Symposium no. 30. Vol. 30. University of Toronto: International Astronomical Union. p. 57. Bibcode:1967IAUS...30...57E.
  7. Catanzaro, G. (2010). "First spectroscopic analysis of β Scorpii C and β Scorpii E. Discovery of a new Hg Mn star in the multiple system β Scorpii". Astronomy and Astrophysics. 509: A21. Bibcode:2010A&A...509A..21C. doi:10.1051/0004-6361/200913332.
  8. Rumrill, H. B. (June 1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific. San Francisco, California. 48 (283): 139. Bibcode:1936PASP...48..139R. doi:10.1086/124681. S2CID 120743052.
  9. "Naming Stars". IAU.org. Retrieved 18 June 2018.
  10. Mason, Brian D.; Hartkopf, William I.; Tokovinin, Andrei (September 2010), "Binary Star Orbits. IV. Orbits of 18 Southern Interferometric Pairs", The Astronomical Journal, 140 (3): 735–743, Bibcode:2010AJ....140..735M, doi:10.1088/0004-6256/140/3/735
  11. 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.
  12. Van Flandern, T. C.; Espenschied, P. (1975). "Lunar occultations of beta Scorpii in 1975 and 1976". Astrophysical Journal. 200: 61. Bibcode:1975ApJ...200...61V. doi:10.1086/153760.
  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. Davis, George A. (1944). "The pronunciations, derivations, and meanings of a selected list of star names". Popular Astronomy. 52: 8–30. Bibcode:1944PA.....52....8D.
  15. Aitken, R. G. (1924). "The Zodiacal Constellation Scorpio". Publications of the Astronomical Society of the Pacific. 36 (211): 124–130. Bibcode:1924PASP...36..124A. doi:10.1086/123392. JSTOR 40692425.
  16. Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Revised ed.). New York: Dover Publications. p. 367. ISBN 0-486-21079-0.
  17. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  18. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  19. (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.
  20. (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.
  21. 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. S2CID 118461108.
  22. Können, G. P.; Van Maanen, J. (April 1981), "Planetary occultations of bright stars.", Journal of the British Astronomical Association, 91: 148–157, Bibcode:1981JBAA...91..148K
  23. Bartholdi, P.; Owen, F. (1972). "The Occultation of Beta Scorpii by Jupiter and Io. II. Io". Astronomical Journal. 77: 60–65. Bibcode:1972AJ.....77...60B. doi:10.1086/111245.
  24. "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. Retrieved 2017-05-16.
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