Westerlund 1-75

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^[7] (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.

Westerlund 1-75 compared to the other 3 RSGs in the Westerlund 1 star cluster.

Westerlund 1-75

Westerlund 1 super star cluster (north is towards top left). The location of Wd 1-75 is circled. Credit: ESO
Observation data Epoch J2000      Equinox J2000
Constellation	Ara[1]
Right ascension	16h 47m 08.92s[2]
Declination	−45° 49′ 58.5″[2]
Apparent magnitude (V)	16.7
Characteristics
Evolutionary stage	Red supergiant
Spectral type	M1[3] - M4Ia[4]
Apparent magnitude (J)	6.933[5]
Apparent magnitude (H)	4.673[5]
Apparent magnitude (K)	3.28[5]
Astrometry
Radial velocity (Rv)	−50.6±2.9[2] km/s
Proper motion (μ)	RA: −2.029[2] mas/yr Dec.: −4.248[2] mas/yr
Parallax (π)	0.0893±0.1477 mas[2]
Distance	4,120+660 −330[6] pc
Details
Radius	722±36[3] R☉
Luminosity	120,000±14,000[3] L☉
Temperature	3,600[7] - 4,000[3] K
Other designations
Westerlund 1 BKS E, 2MASS J16470892-4549585, Gaia DR3 5940199877892579584
Database references
SIMBAD	data

The star is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.^[8] It occupies the upper right corner of the Hertzsprung-Russell diagram. Using the effective temperature of 3,600 K,^[7] the bolometric luminosity of 68,000 L_☉^[7] and the solar effective temperature of 5,772 K,^[9] 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.^[10]

Westerlund 1-75 is surrounded by extended nebula, although it appears less massive than nebulae around typical red supergiant stars.^[11]

See also

• List of largest known stars

Notes

1. ${\displaystyle {\sqrt {\left({\frac {5772}{3600}}\right)^{4}\cdot 10^{4.83}}}\approx 668.42\ R_{\odot }}$