HD 5980
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Tucana |
| Right ascension | 00h 59m 26.569s |
| Declination | –72° 09′ 53.91″ |
| Apparent magnitude (V) | 11.31 |
| Characteristics | |
| Spectral type | LBV + WN4 + OI |
| U−B color index | −0.99 |
| B−V color index | −0.18 |
| Variable type | LBV and EA |
| Astrometry | |
| Radial velocity (Rv) | −20 km/s |
| Proper motion (μ) |
RA: −3.5 mas/yr Dec.: −2.4 mas/yr |
| Distance | 200,000 ly (64,000pc) |
| Absolute magnitude (MV) | −8.1 (−7.1/−6.8/−6.7) |
| Orbit | |
| Primary | HD 5980 A |
| Companion | HD 5980 B |
| Period (P) | 19.2656±0.0009 days |
| Semi-major axis (a) | 151±4 R☉ |
| Eccentricity (e) | 0.27±0.02 |
| Inclination (i) | 86° |
| Periastron epoch (T) | 2451424.97±0.25 |
|
Argument of periastron (ω) (primary) |
134±4° |
|
Semi-amplitude (K1) (primary) |
214±6 km/s |
|
Semi-amplitude (K2) (secondary) |
200±6 km/s |
| Orbit | |
| Primary | HD 5980 C |
| Period (P) | 96.56±0.01 days |
| Eccentricity (e) | 0.815 |
| Periastron epoch (T) | 2522451183.40±0.22 |
|
Argument of periastron (ω) (primary) |
252±3.3° |
|
Semi-amplitude (K1) (primary) |
81±4 km/s |
| Details | |
| A | |
| Mass | 61 M☉ |
| Radius | 24 (21 – 280) R☉ |
| Luminosity | 2,200,000 (2,000,000 – 10,000,000) L☉ |
| Temperature | 45,000(21,000 – 53,000) K |
| Metallicity [Fe/H] | −1.0 dex |
| Rotational velocity (v sin i) | 250 km/s |
| B | |
| Mass | 66 M☉ |
| Radius | 22 R☉ |
| Luminosity | 1,800,000 L☉ |
| Temperature | 45,000 K |
| Rotational velocity (v sin i) | <400 km/s |
| Age | 2.6 Myr |
| C | |
| Mass | 34 M☉ |
| Radius | 24 R☉ |
| Luminosity | 708,000 L☉ |
| Temperature | 34,000 K |
| Metallicity [Fe/H] | ≅ −0.7 dex |
| Rotational velocity (v sin i) | 120 km/s |
| Age | 3.1 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 5980 is a multiple star system in NGC 346 in the Small Magellanic Cloud (SMC) and is one of the brightest stars in the SMC.
HD 5980 has at least three components amongst the most luminous stars known: the unusual primary has a Wolf–Rayet spectrum and has produced a luminous blue variable (LBV) outburst; the secondary, also a Wolf–Rayet star, forms an eclipsing spectroscopic binary with the primary star; and a more distant O-type supergiant is also likely to be a binary.
HD 5980 was first recorded in 1901 as the first object in a list of southern sky objects having peculiar spectra. It was described as "Type V", referring to the Secchi class for stars with emission lines.
It was formally named HD 5980 in the first Henry Draper Catalogue where it was given the spectral type of Oa indicating strong emission bands. The spectral type was later refined to Wa when the emission line "O" stars were recognised as a separate class.
Later observations detected spectral and brightness variations and eclipses, but it was thought to be a simple WR/OB binary. Absorption lines in the spectrum that did not move during the binary orbit eventually led to the conclusion that HD 5980 was a triple system with a close eclipsing binary and a more distant class O supergiant.
In 1993, the spectrum began to change and the brightness increased, beginning a dramatic change that has been interpreted as a unique type of LBV eruption. Since then the star has been intensively observed and modelled.
HD 5980 is visually a single star, but the spectrum reveals three hot luminous components. The physical parameters of the three stars are uncertain because of the difficulties of resolving their spectra, the partial eclipses, apparent intrinsic variations with the orbital phase, and the strong variability of at least one component. The calibration of spectral features to physical characters such as temperature has historically been complicated by the low metallicity of objects in the SMC.
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