Beta Capricorni

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title: "Beta Capricorni" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["b-type-main-sequence-stars", "a-type-main-sequence-stars", "k-type-bright-giants", "double-stars", "multiple-star-systems", "capricornus", "bayer-objects", "bright-star-catalogue-objects", "durchmusterung-objects", "flamsteed-objects", "henry-draper-catalogue-objects", "hipparcos-objects", "stars-with-proper-names"] description: "Star system in the constellation Capricornus" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Beta_Capricorni" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Star system in the constellation Capricornus ::

| name = β Capricorni | image = |image=Capricornus constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=12|mark_link=Beta |x=790|y=410 | caption = 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. | epoch = J2000.0 | constell = Capricornus | component1 = β1 Cap | ra1 = | dec1 = | appmag_v1 = +3.05 | component2 = β2 Cap | ra2 = | dec2 = | appmag_v2 = +6.09 | component1 = β1 Cap | class = K0II+B8V | b-v = +0.79 | u-b = +0.27 | variable = | component2 = β2 Cap | type2 = main sequence | class2 = A0III | b-v2 = −0.02 | u-b2 = −0.11 | variable2 = | component1 = β1 Cap | radial_v = −19.0 | prop_mo_ra = +44.133 | prop_mo_dec = +0.360 | pm_footnote = | parallax = 8.3966 | p_error = 0.6348 | parallax_footnote = | absmag_v = −2.03 | component2 = β2 Cap | prop_mo_ra2 = +44.411 | prop_mo_dec2 = −0.637 | pm_footnote2 = | parallax2 = 9.8983 | p_error2 = 0.3071 | parallax_footnote2 = | absmag_v2 = +1.03 | reference = | primary = Aa | name = Ab | period = 3.762 | axis = 0.049 | eccentricity = 0.452 | inclination = 75.1 | k1 = 22.4 | k2 = 19.6 | reference = | primary = Ab1 | name = Ab2 | period_unitless = 8.677 days | eccentricity = 0.340 | k1 = 35.1 | reference = | primary = Ba | name = Bb | period = 400 | axis = 0.689 | eccentricity = 0.458 | inclination = 125.2 | component1 = β1 Cap Aa | mass = | radius = 31.4 | temperature = 4,870 | luminosity = 501 | age_myr = 230 | component1 = β Cap Ab1 | mass = 4.22 | luminosity = 112 | age_myr = 230 | component2 = β Cap Ab2 | mass2 = 0.94 | age_myr2 = 230 | component1 = β Cap Ba | mass = 2.53 | temperature = 11,188 | luminosity = 55 | radius = 1.98 | gravity = 4.18 | age_myr = 230 | component2 = β Cap Bb | mass2 = 1.23 | age_myr2 = 230 | names = | component1 = β1 Cap | names1 = | component2 = β2 Cap | names2 = | Simbad=bet01+Cap | sn=β1 Cap | Simbad2=bet02+Cap | sn2=β2 Cap Beta Capricorni is a multiple star system in the constellation of Capricornus. Its name is a Bayer designation that is Latinized from β Capricorni, and abbreviated Beta Cap or β Cap. Based on Parallax measurements, it is located at a distance of approximately 390 light years from the Sun. The system is drifting closer with a line of sight velocity of −19 km/s. Because it is positioned near the ecliptic, Beta Capricorni can be occulted by the Moon, and also (rarely) by planets.

The system is believed to consist of five stars. 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 , the traditional name of the system) 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).

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. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. 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.

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. Consequently, the Chinese name for Beta Capricorni itself is 牛宿一 (Niú Su yī, ).

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. If gravitationally bound, they would take around a million years to complete one orbit. 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, and the close binary system Beta Capricorni Ab. They are separated by 0.04 arcseconds (5 AU) and have an orbital period of 3.77 years. Beta1 Capricorni is sufficiently close to the ecliptic to be occulted by the Moon.

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. The Ab1 and Ab2 components are separated by about 0.1 au 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 have a published spectral class, but is estimated to have 0.94 times the mass of the Sun.

Beta² Capricorni

Beta2 Capricorni is a simpler single-lined spectroscopic binary. The visible component, Beta Capricorni Ba, is an A-type star with 40 times the luminosity of the Sun. The companion, Beta Capricorni Bb, is approximately 3 arcseconds from Ba and has a mass slightly higher than the Sun. Ba is classified as a mercury-manganese star, a chemically peculiar star with unusually strong mercury and manganese lines in its spectrum.

Despite the luminosity class of III, the visible component of Beta2 Capricorni is apparently a main sequence star.

References

References

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