Westerlund 1 W237, also known as Wd 1-237 or Westerlund 1 BKS B, is a possible

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...

(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 first constellati ...

Ara Ara may refer to: Biology * ''Ara'' (bird), a genus of parrots * Ara (fish) (''Niphon spinosus''), a species of fish * L-arabinose operon, also known as ara Places * Ara (mountain), a mountain in Armenia * Ara, Armenia, a village in Armenia ...

. It is one out of four 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 kiloparsec, kpc (12,000 ly) away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discover ...

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 ...

. As a red supergiant, it would be one of the largest known stars and one of the most luminous of its type.

Physical characteristics

Westerlund 1 W237 is classified as a luminous cool

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

emitting most of its energy in the

infrared spectrum Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

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

Westerlund 1 W26 Westerlund 1 W26 (commonly abbreviated to W26) or Westerlund 1 BKS AS is a red supergiant located at the outskirts of the Westerlund 1 super star cluster. It is one of the List of largest known stars, largest known stars and the List of ...

, and moreover directly comparable to that of

VY Canis Majoris VY Canis Majoris (abbreviated to VY CMa) is an extreme oxygen-rich red hypergiant or red supergiant (O-rich RHG or RSG) and pulsating variable star from the Solar System in the slightly southern constellation of Canis Major. It is on ...

. 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 Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electromagnetic energy emitted per ...

of , the radius of Westerlund 1 W237 would be 1,241 times the

solar radius Solar radius is a unit of distance used to express the size of objects 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 ...

(), 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 Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

. 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 consi ...

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

Distance

The distance of Westerlund 1 W237 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 In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...

with a luminosity only around .

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

gives a parallax of for W237, 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, corresponding to a distance of ().

References

{{DEFAULTSORT:Westerlund 1 W237 Ara (constellation) M-type supergiants M-type giants J16470309-4552189

Physical characteristics

Distance

See also

References