Kappa Centauri

Kappa Centauri (κ Cen, κ Centauri) is a binary star in the southern constellation of Centaurus. With an apparent visual magnitude of +3.14,^[2] it can be viewed with the naked eye on a dark night. Parallax measurements place it at an estimated distance of 400 light-years (120 parsecs) from Earth.^[3]

κ Centauri

Location of κ Centauri (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Centaurus
Right ascension	14h 59m 09.68494s[1]
Declination	−42° 06′ 15.1069″[1]
Apparent magnitude (V)	+3.14[2] (3.34 + 4.71)[3]
Characteristics
Spectral type	B2V + B3V[3]
U−B color index	−0.805[2]
B−V color index	−0.204[2]
Variable type	Candidate β Cep[4]
Astrometry
Radial velocity (Rv)	+8.0[5] km/s
Proper motion (μ)	RA: −17.62 mas/yr[1] Dec.: −22.51 mas/yr[1]
Parallax (π)	8.14±0.33 mas[3]
Distance	400 ± 20 ly (123 ± 5 pc)
Absolute magnitude (MV)	–2.2[6]
Details
κ Cen A
Mass	8.38±0.27[3] M☉
Radius	4.4±0.7[7] R☉
Luminosity	2,500[7] L☉
Surface gravity (log g)	4.02±0.20[7] cgs
Temperature	20,900[3] K
Rotational velocity (v sin i)	10[8] km/s
Age	18.2±3.2[9] Myr
κ Cen B
Mass	4.41±0.36[3] M☉
Temperature	18,800[3] K
Orbit[3]
Period (P)	58.52±1.50 years
Semi-major axis (a)	0.287″±0.008″
Eccentricity (e)	0.304±0.009
Inclination (i)	90.9±0.5°
Longitude of the node (Ω)	156.1±0.5°
Periastron epoch (T)	2011.10±0.30
Argument of periastron (ω) (secondary)	215.1±2.0°
Other designations
CD−41°9342,FK5 553, HD 132200, HIP 73334, HR 5576, SAO 225344.[10]
Database references
SIMBAD	data

Characteristics

This is a spectroscopic binary system where the presence of an orbiting companion is revealed by shifts in the absorption lines caused by the Doppler effect. They take 58 years to complete an orbit, have a small eccentricity of 0.304, and are seen orbiting nearly edge-on.^[3]

A light curve for Kappa Centauri, plotted from TESS data.^[11]

The primary component has about 8.4 times the Sun's mass^[3] and four times the Sun's radius.^[7] It has a stellar classification of B2V,^[3] indicating that it is in the main sequence stage of its stellar evolution. An effective temperature of 20,900 K^[3] in the outer envelope is what gives it the blue-white hue of a B-type star.^[12] It is a candidate Beta Cephei variable that shows line-profile variations in its spectrum. However, the nature of the variability remains uncertain because of the binary nature of the system.^[4]

The secondary is also a B-type main-sequence star, of spectral class B3V. It has 4.4 times the Sun's mass and an effective temperature of 18,800 K.^[3]

This system is a proper motion member of the Upper Centaurus–Lupus sub-group in the Scorpius–Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.^[6]

In Chinese astronomy

In Chinese, 騎官 (Qí Guān), meaning Imperial Guards, refers to an asterism consisting of κ Centauri, γ Lupi, δ Lupi, β Lupi, λ Lupi, ε Lupi, μ Lup, π Lupi, ο Lupi and α Lupi.^[13] Consequently, the Chinese name for κ Centauri itself is 騎官三 (Qí Guān sān, English: the Third Star of Imperial Guards.).^[14] From this Chinese name, the name Ke Kwan has appeared.^[15]

See also

• Traditional Chinese star names