Westerlund 1-237


Westerlund 1-237 or Wd 1-237 is a possible red supergiant in the constellation of ara. It is one out of 4 known red supergiants in the Westerlund 1 super star cluster, although its outlying position, spectrum, and parallax, suggest it could be a foregound giant. As a red supergiant, it would be one of the largest known stars.

Physical characteristics

Westerlund 1-237 is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum. It is sorrounded by a radio nebula which is similar in mass to those of Westerlund 1-20 and Westerlund 1-26, and moreover directly comparable to that of VY Canis Majoris. The elliptical structure of this nebula however indicates that it has been less affected by the cluster wind of Westerlund 1. The outflow velocity for the RSG wind is assumed to be around 30 km/s. The nebula itself seems to have a mass of and a radius of about 0.11 parsecs. This results in a kinematic age around 3,600 years and a time averaged mass loss rate of per year.
The star occupies the upper right corner of the Hertzsprung-Russell diagram. With an effective temperature of 3,600 K and a bolometric luminosity of, the radius of Westerlund 1-237 would be 1,245 times the solar radius, which would corresponds to a volume 1.93 billion times bigger than the sun. If placed at the center of the Solar System, the star would engulf the orbit of Jupiter.

Distance

The distance of Westerlund 1 is assumed to be around or based on it being commonly thought of as a member of the Westerlund 1 star cluster. Another source suggests a similar distance of.
Westerlund's 1987 analysis assigned a spectral type of M6+ III to W1-237 and considered it to be a foregound giant with a luminosity only around. Gaia Data Release 2 gives a parallax of for W1-237, implying a distance of and a luminosity of with a corresponding radius of.