Theta Centauri

Theta Centauri or θ Centauri, officially named Menkent (/ˈmɛŋkɛnt/),^[9][10] is a single^[11] star in the southern constellation of Centaurus, the centaur. With an apparent visual magnitude of +2.06,^[2] it is the fourth-brightest member of the constellation. Based on parallax measurements obtained during the Hipparcos mission, it is about 58.8 light-years (18.0 parsecs) distant.^[1] It has a relatively high proper motion, traversing the celestial sphere at the rate of 0.73 arcsecond/yr.^[12] This suggests that Menkent may have originated in the outer disk of the Milky Way and is merely passing through the solar neighborhood.^[13]

Theta Centauri

Location of θ Centauri (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Centaurus
Right ascension	14h 06m 40.94752s[1]
Declination	−36° 22′ 11.8371″[1]
Apparent magnitude (V)	+2.06[2]
Characteristics
Evolutionary stage	Red clump[3]
Spectral type	K0 III[4]
U−B color index	+0.90[2]
B−V color index	+0.99[2]
Astrometry
Radial velocity (Rv)	+1.3[5] km/s
Proper motion (μ)	RA: −520.53[1] mas/yr Dec.: −518.06[1] mas/yr
Parallax (π)	55.45±0.20 mas[1]
Distance	58.8 ± 0.2 ly (18.03 ± 0.07 pc)
Absolute magnitude (MV)	0.87[6]
Details
Mass	1.27[3] M☉
Radius	10.77±0.45[3] R☉
Luminosity	56.0+2.6 −2.5[3][a] L☉
Surface gravity (log g)	2.61±0.09[7] cgs
Temperature	4,853±41[7] K
Metallicity [Fe/H]	−0.047±0.032[7] dex
Other designations
Menkent, θ Cen, Theta Cen, 5 Centauri, CD−35° 9260, FK5 520, HD 123139, HIP 68933, HR 5288, SAO 205188, LHS 2858[8]
Database references
SIMBAD	data

Nomenclature

θ Centauri, Latinised to Theta Centauri, is the star's Bayer designation.

It bore the traditional name of Menkent derived from the Arabic word مَنْكِب‎ (mankib) for "shoulder" (of the Centaur), apparently blended with a shortened form of "kentaurus" (centaur). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[14] to catalog and standardize proper names for stars. The WGSN approved the name Menkent for this star on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.^[10]

In Chinese, 庫樓 (Kù Lóu), meaning arsenal, refers to an asterism consisting of Theta Centauri, Zeta Centauri, Eta Centauri, 2 Centauri, HD 117440, Xi¹ Centauri, Gamma Centauri, Tau Centauri, D Centauri and Sigma Centauri.^[15] Consequently, the Chinese name for Theta Centauri itself is 庫樓三 (Kù Lóu sān, English: the Third Star of Arsenal).^[16]

Properties

This is an evolved giant star with a stellar classification of K0 III^[4] and 1.27 times the mass of the Sun. It is believed to be fusing helium into carbon and heavier elements within its core, qualifying it as a red clump star.^[3] It is a southern analog to Pollux, the brightest star in Gemini and the closest giant to the Sun.^[13] It is over ten times larger than the Sun and 60 times more luminous.^[3] The outer envelope has an effective temperature of 4,853 K,^[7] giving it the orange-hued glow of a cool, K-type star.^[17] Soft X-ray emission has been detected from this star, which has an estimated X-ray luminosity of 1.4 × 10²⁷ erg s⁻¹.^[18]

See also

• List of nearest giant stars

Notes

1. Calculated using absolute bolometric magnitude of +0.37±0.05 via the equation 10^{0.4(4.74−M_bol)}.