Beta Scorpii

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Beta 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]
Spectral type B1V + B2V
U−B color index –0.08 / –0.70[3]
B−V color index –0.08 / –0.02[3]
HR 5984
Radial velocity (Rv) –1.0[4] 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)
HR 5985
Radial velocity (Rv) –3.6[4] 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)
HR 5984
Mass 10[5] M
Radius 19 R
Luminosity 20,000[5] L
Temperature 27,000[5] K
Rotational velocity (v sin i) 100[6] km/s
HR 5985
Temperature 22,000[5] K
Rotational velocity (v sin i) 65[6] km/s
Other designations
Acrab, Elacrab, Graffias, Grassias, 8 Scorpii, ADS 9913.
A: β1 Sco, BD–19 4307, HD 144217, HIP 78820, HR 5984, SAO 159682.
B: β2 Sco, BD–19 4308, HD 144218, HIP 78821, HR 5985.
Database references

Beta Scorpii (β Scorpii, abbreviated Beta Sco, β Sco) is a multiple star system in the southern zodiac constellation of Scorpius.

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

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 the hierarchy of orbiting components in this 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[7]) and β Scorpii Ab, separated by 1.42 milliarcseconds and an orbital period of 6.82 days.[8]

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.

This brings the total number of stars in the system to six. (There is no D component; this is now an artifact of earlier system models.[8])


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).[9]

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,[10][11] a name it shared with Xi Scorpii.

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] 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.[13] 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.[7]

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


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


The two most massive members of the system have the spectrum of B-type main sequence stars. Component C has a stellar classification of B2V.[8] They are both hot stars at least 10 times as massive as the Sun, and will have short lives. Both are expected to end their stellar evolution with massive Type II supernova explosions.

The Beta 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).[14] A recent analysis of the HR diagram position for the most massive star Beta-1 Scorpii A[14] estimates its effective temperature to be 26,240 Kelvin with a luminosity of 19,500 Suns, consistent with an isochronal age of 11 million years and an estimated mass of 12 solar masses.

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.

In culture[edit]

Beta Scorpii appears on the flag of Brazil, symbolising the state of Maranhão.[15]


  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, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, 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 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 
  4. ^ 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 
  5. ^ a b c d Kaler, James B. "GRAFFIAS (Beta Scorpii)". University of Illinois. Retrieved 2010-02-20. 
  6. ^ a b 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 
  7. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  8. ^ a b c 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 
  9. ^ 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]. 
  10. ^ R. G. Aitken Publications of the Astronomical Society of the Pacific Vol. 36, No. 211 (June, 1924), pp. 124-130 JSTOR 40692425
  11. ^ Allen, R. H., (1899) Star-names and Their Meanings, New York: G. E. Stechert, p. 367.
  12. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  13. ^ "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 12 October 2016. 
  14. ^ a b 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:1112.1695Freely accessible. Bibcode:2012ApJ...746..154P. doi:10.1088/0004-637X/746/2/154. 
  15. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. Archived from the original on June 28, 2009. 

External links[edit]