| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ara |
| Right ascension | 16h 47m 08.92s[1] |
| Declination | −45° 49′ 58.5″[1] |
| Apparent magnitude (V) | 16.7 |
| Characteristics | |
| Evolutionary stage | Red supergiant |
| Spectral type | M1[2] - M4Ia[3] |
| Apparent magnitude (J) | 6.933[4] |
| Apparent magnitude (H) | 4.673[4] |
| Apparent magnitude (K) | 3.28[4] |
| Astrometry | |
| Radial velocity (Rv) | −50.6±2.9[1] km/s |
| Proper motion (μ) | RA: −2.029[1] mas/yr Dec.: −4.248[1] mas/yr |
| Parallax (π) | 0.0893 ± 0.1477 mas[1] |
| Distance | 4,120+660 −330[5] pc |
| Details | |
| Radius | 722±36[2] R☉ |
| Luminosity | 120,000±14,000[2] L☉ |
| Temperature | 3,600[6] - 4,000[2] K |
| Other designations | |
Westerlund 1 BKS E, 2MASS J16470892-4549585, Gaia DR3 5940199877892579584 | |
| Database references | |
| SIMBAD | data |
Westerlund 1 W75 or Wd 1-75 is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius is calculated to be around 668 solar radii[6] (4.65 × 108 km, 3.10 au). This corresponds to a volume 298 million times bigger than the Sun. If placed at the center of the Solar System, Westerlund 1-75 would engulf the inner limits of the asteroid belt.
The star is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.[7] It occupies the upper right corner of the Hertzsprung-Russell diagram. Using the effective temperature of 3,600 K,[6] the bolometric luminosity of 68,000 L☉[6] and the solar effective temperature of 5,772 K,[8] the radius of Westerlund 1-75 can be calculated using the Stefan-Boltzmann law at 668 R☉.[a]
Like Westerlund 1-20, Westerlund 1 W26 and Westerlund 1-237, Westerlund 1-75 was observed to be a radio source, however it is weakest along the RSGs in its cluster and remains unresolved at any wavelength.[9]
Westerlund 1-75 is surrounded by extended nebula, although it appears less massive than nebulae around typical red supergiant stars.[10]
