Beta Capricorni

β¹/β² Capricorni
Beta Capricorni circled on a chart of Capricorn; the map is to be held up as with most sky maps so that the right of page is west.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Capricornus
β1 Cap
Right ascension 20h 21m 0.6667s[1]
Declination 14° 46′ 53.067″[1]
Apparent magnitude (V) +3.05[citation needed]
β2 Cap
Right ascension 20h 20m 46.5479s[2]
Declination 14° 47′ 05.604″[2]
Apparent magnitude (V) +6.09[citation needed]
Characteristics
Spectral type K0II+B8V/A0III
U−B color index 0.28/−0.11
B−V color index 0.79/−0.02
Variable type none
Astrometry
Parallax (π)9.98±1.09 mas[3]
Distanceapprox. 330 ly
(approx. 100 pc)
Absolute magnitude (MV)−2.03/+1.03[4]
Details
β1 Cap Aa
Mass4[5] M☉
Radius35[5] R☉
Luminosity600[5] L☉
Temperature4,900[5] K
β Cap Ab1
Mass3.28[6] M☉
β Cap Ab2
Mass0.94[6] M☉
β Cap Ba
Mass2.53[6] M☉
β Cap Bb
Mass1.23[6] M☉
Other designations
Dabih, Dabikh, Dikhabda, 9 Capricorni, FK5 762, WDS J20210-1447AB
β1 Cap: BD−15°5629, HD 193495, HIP 100345, HR 7776, WDS J20210-1447A
β2 Cap: BD−15°5626, HD 193452, HIP 100325, HR 7775, WDS J20210-1447B
Database references
SIMBADβ Cap
β1 Cap
β2 Cap

Beta Capricorni (β Capricorni, abbreviated Beta Cap, β Cap) is a multiple star system in the constellation of Capricornus and located 328 light-years from the Sun. Because it is near the ecliptic, Beta Capricorni can be occulted by the Moon,[7] and also (rarely) by planets.

The system is believed to consist of five stars.[8] With binoculars or a small telescope, Beta Capricorni can be resolved into a binary pair. The brighter of the two is designated Beta1 Capricorni or Beta Capricorni A; the dimmer, Beta2 Capricorni or Beta Capricorni B. Both are themselves made up of multiple stars. Beta1 Capricorni has three components; a single star designated Beta Capricorni Aa (formally named Dabih /ˈdeɪbiː/, the traditional name of the system)[9][10] and a binary pair, Beta Capricorni Ab (whose two components are designated Beta Capricorni Ab1 and Ab2). Beta2 Capricorni is also a binary pair, with components designated Beta Capricorni Ba and Bb.

Two other nearby stars were discovered by John Herschel. Sometimes referred to as Beta Capricorni D and E, it is unclear whether they are simply optical doubles or part of the Beta Capricorni system.

Nomenclature

β Capricorni (Latinised to Beta Capricorni) is the system's Bayer designation; β1 and β2 Capricorni those of its two constituents. The designations of the two constituents as Beta Capricorni A and B, and those of the sub-components - Beta Capricorni Aa, Ab, Ab1, Ab2, Ba and Bb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[11]

Beta Capricorni bore the traditional name Dabih, deriving from the Arabic الذابح al-dhābiḥ "the butcher", with Beta1 and Beta2 subsequently named Dabih Major and Dabih Minor, respectively.[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[14] It approved the name Dabih for the component Beta Capricorni Aa on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[10]

In Chinese, 牛宿 (Niú Su), meaning Ox (asterism), refers to an asterism consisting of Beta Capricorni, Alpha2 Capricorni, Xi2 Capricorni, Pi Capricorni, Omicron Capricorni and Rho Capricorni.[15] Consequently, the Chinese name for Beta Capricorni itself is 牛宿一 (Niú Su yī, English: the First Star of Ox).[16]

Properties

Beta1 Capricorni is the brighter of the two components with an apparent magnitude of +3.05, while the dimmer Beta2 Capricorni has an apparent magnitude of +6.09. The two components are separated by 3.5 arcminutes on the sky, putting them at least 21,000 AU (0.34 light-years) apart. They take approximately 700,000 years to complete one orbit.

Aa
Sep. = 0.05″
Ab1
Period = 8.7d
Ab2
Ba
Sep. = 3″
Bb

Hierarchy of orbits in the β Capricorni system

Beta1 Capricorni

Beta1 Capricorni is the more complex of the pair and has a spectrum that is difficult to interpret. Its dominant pair of stars are the orange K-type bright giant Beta Capricorni Aa, with an apparent magnitude of +3.08, and the close binary system Beta Capricorni Ab1 with an apparent magnitude of +7.20. They are separated by 0.04 arcseconds (5 AU[5]) and have an orbital period of 3.77 years.[6] Beta1 Capricorni is sufficiently close to the ecliptic to be occulted by the Moon.[5]

The Aa component has a surface temperature of 4,900 K, a radius 35 times that of the Sun, and a luminosity 600 times that of the Sun.[5] The Ab1 and Ab2 components are separated by about 0.1 au[5] and complete an orbit around each other every 8.68 days. The Ab1 component is a B-type main-sequence star, while Ab2 does not has a spectral class, but is estimated to have 0.94 times the mass of the Sun.[6]

Beta2 Capricorni

Beta2 Capricorni is simpler and more studied. Its brighter component, Beta Capricorni Ba, has a magnitude of 6.1 and is an A0-giant with 40 times the luminosity of the Sun. The companion, Beta Capricorni Bb, is approximately 3 arcseconds from Ba. Ba is unusual for having large amounts of mercury and manganese in its atmosphere.

References

  1. ^ a b Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. ^ van Leeuwen, Floor (13 August 2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. eISSN 1432-0746. ISSN 0004-6361.
  4. ^ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  5. ^ a b c d e f g h "Dabih". stars.astro.illinois.edu. Retrieved 2025-07-22.
  6. ^ a b c d e f Tokovinin, Andrei (2018-03-01). "The Updated Multiple Star Catalog". The Astrophysical Journal Supplement Series. 235 (1): 6. arXiv:1712.04750. Bibcode:2018ApJS..235....6T. doi:10.3847/1538-4365/aaa1a5. ISSN 0067-0049.{{cite journal}}: CS1 maint: postscript (link)
  7. ^ White, Nathaniel M.; Feierman, Barry H. (September 1987). "A Catalog of Stellar Angular Diameters Measured by Lunar Occultation". Astronomical Journal. 94: 751. Bibcode:1987AJ.....94..751W. doi:10.1086/114513.
  8. ^ "Displaying next number in catalog HIP => 100345". Multiple Star Catalog. Archived from the original on 2018-07-26. Retrieved 2018-07-26.
  9. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  10. ^ a b "Naming Stars". IAU.org. Retrieved 18 June 2018.
  11. ^ 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].
  12. ^ Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 140. ISBN 0-486-21079-0. {{cite book}}: ISBN / Date incompatibility (help)
  13. ^ "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Retrieved 22 May 2016.{{cite web}}: CS1 maint: postscript (link)
  14. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  15. ^ (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.
  16. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2009-09-29 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
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