HR 5171
 Combined optical and infrared image Credit: ESO/Digitized Sky Survey 2 |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Centaurus |
| A | |
| Right ascension | 13h 47m 10.875s |
| Declination | −62° 35′ 23.06″ |
| Apparent magnitude (V) | 6.1 - 7.5 |
| B | |
| Right ascension | 13h 47m 10.224s |
| Declination | −62° 35′ 17.40″ |
| 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 |
| Proper motion (μ) |
RA: −2.94 mas/yr Dec.: −-2.54 mas/yr |
| Parallax (π) | 1.35 ± 1.59 mas |
| Distance | 11,700 ly (3,600pc) |
| Absolute magnitude (MV) | −9.2 + −5.8 |
| Orbit | |
| Primary | Aa |
| Companion | Ab |
| Period (P) | 1,304 ± 6 days |
| Semi-major axis (a) | ~2,000 R☉ |
| Eccentricity (e) | 0 |
| Inclination (i) | >60° |
| Details | |
| Aa | |
| Mass | 27 - 36 M☉ |
| Radius | 1,490 ± 540 R☉ |
| Luminosity | 630,000 L☉ |
| Surface gravity (log g) | −0.5 ± 0.6 cgs |
| Temperature | 4,290 ± 7605,000 K |
| Ab | |
| Mass | 3 - 6 M☉ |
| Radius | 312 × 401 R☉ |
| Temperature | 4,800 - 5,200 K |
| Age | 3.5 Myr |
| B | |
| Luminosity | 316,000 L☉ |
| Surface gravity (log g) | 3.0 - 3.5 cgs |
| Temperature | 26,000 K |
| Age | 4 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
HR 5171, also known as V766 Centauri, is a triple star system in the constellation Centaurus, around 12,000 light years from Earth. It contains the largest known yellow hypergiant star which is also an eclipsing binary.
HR 5171 was named by inclusion in the Harvard Revised Catalogue, later published as the Bright Star Catalogue. It was entry #5171, listed at magnitude 6.23 and spectral type K. HR 5171 was catalogued as a double star in 1927.
In 1956 HR 5171 was recorded at magnitude 6.4, spectral type G5p, and profoundly reddened. In 1966 Corben recorded it as magnitude 6.51 and spectral type G5p, and noted it as being variable. A 1969 catalogue records a visual magnitude of 5.85 and a spectral type of A7V, presumably a case of mistaken identity. In 1971, HR 5171 A was identified as a G8 hypergiant, reddened by over 3 magnitudes of interstellar extinction and also by half a magnitude of extinction from circumstellar material. In 1979 it was confirmed as one of the brightest known stars with an absolute visual magnitude (MV) of −9.2. The G8 spectral type was adjusted to K0 Ia+ in the revised MK system.
In 1973 HR 5171 was formally recognised as variable star V766 in Centauri, based on Corben's 1966 catalogue. At the time it was considered a "cool S Doradus variable", a class including stars such as Rho Cassiopeiae that are now known as the yellow hypergiants. These variables are usually classified as semiregular (SRd) due to variations which are sometimes well-defined, at other times nearly constant, and may show unpredictable fading. A detailed study showed variability in both brightness and spectral type with possible periods developing from 430 days to 494 days. The temperature was calculated to vary from nearly 5,000 K to below 4,000 K.
In a 2014 paper, VLTI observations directly determined an unexpectedly large size for HR 5171 and revealed that it is a contact binary. A shell of material around the star has also been directly imaged. In 2016, VLTI observations showed an even larger radius and an unexpectedly cool temperature for a K0 hypergiant.
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