2 Centauri

This article is about g Centauri and is not to be confused with G Centauri.

2 Centauri is a single^[11] star in the southern constellation of Centaurus, located approximately 183 light-years from Earth.^[1] It has the Bayer designation g Centauri;^[10] 2 Centauri is the Flamsteed designation. This object is visible to the naked eye as faint, red-hued star with an apparent visual magnitude of about 4.2. It is moving away from the Earth with a heliocentric radial velocity of +41 km/s.^[6] The star is a member of the HR 1614 supercluster.^[12]

A light curve for V806 Centauri. The main plot shows the long term variability from Hipparcos data,^[13] and the inset plot shows the variability over the 26.5 day period, using data from Tabur et al. (2009).^[14] The green curve shows the best-fit sine wave, which has an amplitude of 18 millimagnitudes.

2 Centauri

Location of 2 Centauri (circled in red)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Centaurus
Right ascension	13h 49m 26.72175s[1]
Declination	−34° 27′ 02.7929″[1]
Apparent magnitude (V)	4.16–4.26[2]
Characteristics
Evolutionary stage	AGB[3]
Spectral type	M5 III[4]
U−B color index	+1.44[5]
B−V color index	+1.49[5]
Variable type	SRb[2]
Astrometry
Radial velocity (Rv)	+40.7±0.7[6] km/s
Proper motion (μ)	RA: −41.68±0.23[1] mas/yr Dec.: −59.77±0.18[1] mas/yr
Parallax (π)	17.82±0.21 mas[1]
Distance	183 ± 2 ly (56.1 ± 0.7 pc)
Absolute magnitude (MV)	+0.51[7]
Details
Mass	1.0[8] M☉
Radius	82.4[9] R☉
Luminosity	767[8] L☉
Surface gravity (log g)	0.65[8] cgs
Temperature	3,438[8] K
Other designations
g Centauri, 2 Cen, V806 Cen, CD−33°9358, GC 18666, HD 120323, HIP 67457, HR 5192, SAO 204875[10]
Database references
SIMBAD	data

This is an evolved red giant star with a stellar classification of M5 III.^[4] In 1951, Alan William James Cousins announced that the star, then called g Centauri, is a variable star.^[15] It was given its variable star designation, V806 Centauri, in 1978.^[16] It is classified as a semiregular variable star and its brightness varies from magnitude +4.16 to +4.26^[2] with a period of 12.57 days.^[17] The star has around 82 times the Sun's radius and is radiating 767 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,438 K.