Westerlund 1-237 or Wd 1-237 is a possible red supergiant (RSG) in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Ara ARA may refer to: Media and the arts * American-Romanian Academy of Arts and Sciences * '' Artistička Radna Akcija'', compilation album released in former Yugoslavia * Associate of the Royal Academy, denoting membership in the British Royal Aca ...

. It is one out of 4 known red supergiants in the

Westerlund 1 Westerlund 1 (abbreviated Wd1, sometimes called Ara Cluster) is a compact young super star cluster about 3.8 kpc (12,000 ly) away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discovered by Ben ...

super star cluster A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. These clusters called "super" because they are relatively more luminous and contain more mass than other young star clusters. ...

, although its outlying position, spectrum, and parallax, suggest it could be a foreground giant. As a red supergiant, it would be one of the largest known stars and one of most luminous of its type.

Physical characteristics

Westerlund 1-237 is classified as a luminous cool supergiant emitting most of its energy in the

infrared spectrum Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

. It is surrounded by a radio nebula which is similar in mass to those of Westerlund 1-20 and

Westerlund 1-26 Westerlund 1-26 or Wd 1-26 is a red supergiant within the outskirts of the Westerlund 1 super star cluster. It is one of the largest known stars discovered so far although its radius is uncertain but is calculated to be , with a possib ...

, 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

(W20 and W26 have pronounced cometary shaped nebulae). 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 3,550 K and a bolometric luminosity of , the radius of Westerlund 1-237 would be 1,241 times the

solar radius Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\tim ...

(), making it larger than the orbit of

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

. The initial mass of W237 has been calculated from its position relative to theoretical

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

ary tracks to be around or for a non-rotating star.

Distance

The distance of Westerlund 1-237 is assumed to be around or based on it being commonly thought of as a member of the Westerlund 1 star cluster (the elliptical shape of its nebula indicates that it might not be near the center of W1, while other RSGs like W20 and W26 are). Another but older 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 foreground giant with a luminosity only around .

Gaia Data Release 2 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, especia ...

gives a parallax of for W1-237, implying a distance of and a luminosity of with a corresponding radius of . In 2020, the parallax was revised to the much smaller value of 0.3370 mas.

References

{{DEFAULTSORT:Westerlund 1-237 Ara (constellation) M-type supergiants M-type giants J16470309-4552189

Physical characteristics

Distance

See also

References