HR 5171
V766 Centauri, also known as HR 5171, 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, while its distance is 3.6 kpc (11,700 light years) from Earth. According to a 2014 publication, the star is 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 days.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Centaurus |
| A | |
| Right ascension | 13h 47m 10.864s |
| Declination | −62° 35′ 22.95″ |
| Apparent magnitude (V) | 6.1 - 7.5 |
| B | |
| Right ascension | 13h 47m 09.953s |
| Declination | −62° 35′ 15.99″ |
| Apparent magnitude (V) | 9.83 |
| Characteristics | |
| A | |
| Spectral type | K0 0-Ia |
| B−V color index | +2.499 |
| Variable type | EB + SDOR? |
| B | |
| Spectral type | B0 Ibp |
| B−V color index | +0.39 |
| Astrometry | |
| Radial velocity (Rv) | −38.20 km/s |
| Distance | 4,900 – 11,700 ly (1,500 – 3,900 pc) |
| A | |
| Proper motion (μ) | RA: −5.648 mas/yr Dec.: −1.797 mas/yr |
| Parallax (π) | 0.2459 ± 0.0514 mas |
| Distance | approx. 13,000 ly (approx. 4,100 pc) |
| Absolute magnitude (MV) | −9.2 |
| B | |
| Proper motion (μ) | RA: −5.715 mas/yr Dec.: −2.143 mas/yr |
| Parallax (π) | 0.3257 ± 0.0126 mas |
| Distance | 10,000 ± 400 ly (3,100 ± 100 pc) |
| Absolute magnitude (MV) | −5.8 |
| Orbit | |
| 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 M☉ |
| Radius | 1,060 – 1,160, 1,315 – 1,575 R☉ |
| Luminosity | 200,000 – 251,000, 630,000+60,000 −55,000 L☉ |
| Surface gravity (log g) | −0.5±0.6 cgs |
| Temperature | 4,287±760 (3,855 - 5,012) K |
| Age | 3.5 Myr |
| Ab | |
| Mass | 5+15 −3 M☉ |
| Radius | 312 - 401, 650±150 R☉ |
| Temperature | 4,800 - 5,200 K |
| B | |
| Luminosity | 160,000 L☉ |
| Surface gravity (log g) | 3.0 - 3.5 cgs |
| Temperature | 26,000 K |
| Age | 4 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
According to a recent publication (2019), not only this is deemed unlikely, but 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).
An optical companion, HR 5171B, may or may not be at the same distance as the yellow supergiant.