Beta Scorpii

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β Scorpii
Scorpius constellation map.svg
Red circle.svg

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]
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]
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[1] mas
Distance 400 ± 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[1] mas
Distance approx. 400 ly
(approx. 120 pc)
Absolute magnitude (MV) –1.83 (Ea: +0.24)[7]
β Sco Aa
Mass 15.0 M
Radius 6.3 R
Luminosity 31,600 L
Temperature 28,000 K
β Sco Ab
Mass 10.4 M
Radius 4.0 R
Luminosity 7,900 L
Temperature 26,400 K
β Sco C
Mass 8.2 M
Radius 2.9 R
Luminosity 3,200 L
Surface gravity (log g) 3.8 cgs
Temperature 24,000 K
Rotational velocity (v sin i) 55 km/s
β Sco Ea
Mass 3.5 M
Radius 2.4 R
Luminosity 126 L
Surface gravity (log g) 4.2 cgs
Temperature 13,000 K
Rotational velocity (v sin i) 5 km/s
Age 6.3 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
SIMBAD β Scorpii
β1 Scorpii
β2 Scorpii

Beta Scorpii (β Scorpii, abbreviated Beta Sco, β Sco) is a multiple star system in the southern zodiac constellation of Scorpius. It has the common name Acrab, technically applying only to the β Scorpii Aa component.


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.

Period = 6.82d
a = 1.42 mas
Period = 610y
a = 3.90″
13.5″ separation
Period = 39y
a = 0.1328″
Period = 10.7d

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 3.9 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[8]) and β Scorpii Ab. They are separated by 1.42 milliarcseconds and have an orbital period of 6.82 days.[9]

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.[10] Some authors have also referred to component Aa as D.[11]

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.[11]


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).[12]

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,[13][14] a name it shared with Xi Scorpii.

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 states that in the case of multiple stars the name should be understood to be attributed to the brightest component by visual brightness.[16] The WGSN approved the name Acrab for β Scorpii Aa on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[8]

It was known as 房宿四 (the Fourth star of the Room) in Chinese.[citation needed]


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


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,[17] 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 are 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.[11]

Component C has a stellar classification of B2 V and a mass of 8 M. It has an effective surface temperatire 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 and unexpectedly low.[7]

Beta Scorpii is 1.01 degree from the ecliptic and can be occulted by the Moon and, very rarely, by planets. The last occultation by a planet took place on 13 May 1971, by Jupiter.[citation needed]

In culture[edit]

Beta Scorpii appears on the flag of Brazil, symbolising the state of Maranhão.[18]


  1. ^ a b c d e f g h i j van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357 
  2. ^ a b Hoffleit, D.; Warren Jr., W. H. (1991). "Entry for HR 2491". Bright Star Catalogue, 5th Revised Ed. (Preliminary Version). CDS.  ID V/50.
  3. ^ a b 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. ^ 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): 99, Bibcode:1966CoLPL...4...99J 
  6. ^ a b Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and their Applications, University of Toronto: International Astronomical Union, 30: 57, Bibcode:1967IAUS...30...57E 
  7. ^ a b c d e f 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. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  9. ^ 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 
  10. ^ 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. 
  11. ^ a b c 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. 
  12. ^ 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:1012.0707Freely accessible [astro-ph.SR]. 
  13. ^ Aitken, R. G. (1924). "The Zodiacal Constellation Scorpio". Publications of the Astronomical Society of the Pacific. 36: 124. Bibcode:1924PASP...36..124A. JSTOR 40692425. doi:10.1086/123392. 
  14. ^ Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Revised ed.). New York: Dover Publications. p. 367. ISBN 0-486-21079-0. 
  15. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  16. ^ "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 12 October 2016. 
  17. ^ 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. Bibcode:2012ApJ...746..154P. arXiv:1112.1695Freely accessible. doi:10.1088/0004-637X/746/2/154. 
  18. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. Retrieved 2017-05-16. 

External links[edit]