Kappa Ursae Majoris

Kappa Ursae Majoris (κ Ursae Majoris, abbreviated Kappa UMa, κ UMa) is a binary star in the constellation of Ursa Major. With a combined apparent magnitude of +3.60,^[9] the system is approximately 358 light-years from Earth.

Kappa Ursae Majoris

Location of κ Ursae Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ursa Major
Right ascension	09h 03m 37.52762s[1]
Declination	+47° 09′ 23.4890″[1]
Apparent magnitude (V)	3.56 (4.16 + 4.54)[2]
Characteristics
Spectral type	A0 IV-V + A0 V[3]
Astrometry
Proper motion (μ)	RA: −36.19[1] mas/yr Dec.: −55.40[1] mas/yr
Parallax (π)	9.10±0.50 mas[1]
Distance	360 ± 20 ly (110 ± 6 pc)
Absolute magnitude (MV)	−1.63[4]
Orbit[5]
Period (P)	13,007.2±9.7 d
Semi-major axis (a)	0.18194 ± 0.00025″
Eccentricity (e)	0.5584±0.0015
Inclination (i)	109.410±0.066°
Longitude of the node (Ω)	105.641±0.080°
Periastron epoch (T)	50404 ± 12
Argument of periastron (ω) (secondary)	355.63±0.36°
Details
κ UMa A
Mass	3.79±0.12[6] M☉
Radius	7.87[7] R☉
Temperature	9,060[7] K
Rotational velocity (v sin i)	201[6] km/s
Other designations
Alkaphrah, κ UMa, 12 Ursae Majoris, BD+47°1633, FK5 341, GC 12503, HD 77327, HIP 44471, HR 3594, SAO 42661, PPM 50987, CCDM J09036+4709AB, WDS J09036+4709AB[8]
Database references
SIMBAD	data

The two components are designated Kappa Ursae Majoris A (officially named Alkaphrah /ælˈkæfrə/, a traditional name of the system)^[10] and B.

Nomenclature

κ Ursae Majoris (Latinised to Kappa Ursae Majoris) is the system's Bayer designation. The designations of the two components as Kappa Ursae Majoris A and B derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).^[11]

The traditional name of the system is Alkafzah (corrupted to Alkaphrah or El Koprah), from the Arabic القفزة al-qafzah "the leap".^[12] (Cf. Alula Borealis and Alula Australis.)

In 2016, the IAU organized a Working Group on Star Names (WGSN)^[13] to catalog 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 Alkaphrah for the component Kappa Ursae Majoris A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.^[10]

In Chinese, 三台 (Sān Tái), meaning Three Steps, refers to an asterism consisting of Kappa Ursae Majoris, Iota Ursae Majoris, Lambda Ursae Majoris, Mu Ursae Majoris, Nu Ursae Majoris and Xi Ursae Majoris. Consequently, the Chinese name for Kappa Ursae Majoris itself is 上台二 (Shàng Tái èr, English: Star of Second Upper Step).^[15]

Properties

Both components of the binary star are white A-type main sequence dwarfs. They have apparent magnitudes of +4.2 and +4.5.^[16] The orbital period of the binary is 35.6 years (13,007.2 days), and the two stars are separated by 0.18 arcseconds.^[17] An infrared excess indicates a debris disk with a mean temperature of 165 K is orbiting the primary at a separation of 55.2 AU.^[7]