HR 5171

V766 Centauri

Location of HR 5171 (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Centaurus
A
Right ascension	13h 47m 10.864s[1]
Declination	−62° 35′ 22.95″[1]
Apparent magnitude (V)	6.1 - 7.5[2]
B
Right ascension	13h 47m 09.953s[3]
Declination	−62° 35′ 15.99″[4]
Apparent magnitude (V)	9.83[4]
Characteristics
A
Spectral type	K0 0-Ia[5]
B−V color index	+2.499[4]
Variable type	EB + SDOR?[6]
B
Spectral type	B0 Ibp[7]
B−V color index	+0.39[4]
Astrometry
Radial velocity (Rv)	−38.20[8] km/s
Distance	4,900 – 12,700 ly (1,500[9] – 3,900[10] pc)
A
Proper motion (μ)	RA: −5.648[1] mas/yr Dec.: −1.797[1] mas/yr
Parallax (π)	0.2459±0.0514 mas[1]
Distance	approx. 13,000 ly (approx. 4,100 pc)
Absolute magnitude (MV)	−9.2[11]
B
Proper motion (μ)	RA: −5.715[3] mas/yr Dec.: −2.143[3] mas/yr
Parallax (π)	0.3257 ± 0.0126 mas[3]
Distance	10,000 ± 400 ly (3,100 ± 100 pc)
Absolute magnitude (MV)	−5.8[12]
Orbit[2]
Primary	Aa
Companion	Ab
Period (P)	1,304±6 days
Semi-major axis (a)	2,028 - 2,195 R☉
Eccentricity (e)	0
Inclination (i)	>60°
Details
Aa
Mass	27 – 36[13][14] M☉
Radius	1,060 – 1,160,[9] 1,315[2] – 1,575[14] R☉
Luminosity	200,000 – 251,000,[9] 630,000+60,000 −55,000[13] L☉
Surface gravity (log g)	−0.5±0.6[13] cgs
Temperature	4,470 – 5,012[9] K
Age	3.5[10] Myr
Ab
Mass	5+15 −3[14] M☉
Radius	312 - 401,[2] 650±150[14] R☉
Temperature	4,800 - 5,200[2] K
B
Radius	20 R☉
Luminosity	160,000[15] L☉
Surface gravity (log g)	3.0 - 3.5[7] cgs
Temperature	26,000[7] K
Age	4[10] Myr
Other designations
V766 Cen, HR 5171, HD 119796, HIP 67261, SAO 252448, CD−61°3988, WDS J13472-6235, AAVSO 1340-62
Database references
SIMBAD	data

HR 5171, also known as V766 Centauri, is a yellow hypergiant in the constellation Centaurus. It is said to be either an extreme red supergiant (RSG) or recent post-red supergiant (Post-RSG) yellow hypergiant (YHG), both of which suggest it is one of the largest known stars. The star's diameter is uncertain but likely to be between 1,100 and 1,600 times that of the Sun. It is 3.6 kpc (11,700 light years) from Earth. It is a variable star, and when it is near its maximum brightness, magnitude 6.1, it is faintly visible to the naked eye under excellent observing conditions.

A 2014 publication hypothesized the star to be a contact binary, sharing a common envelope of material with a smaller yellow supergiant and secondary star, the two orbiting each other every 1,304±6 d. A recent publication (2019) rules out this hypothesis, and the distance of HR 5171 has been revised to 5,200±1,600 light years and its radius to 3-5 AU (i.e. 650 to 1080 times that of the Sun).^[9]

An optical companion, HR 5171B, may or may not be at the same distance as the yellow supergiant.^[9]