16h47m03.1075s, −45° 52′ 18.9572″
Credit: ESO | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ara |
| Right ascension | 16h47m 03.1075s |
| Declination | −45° 52′ 18.9572″ |
| Apparent magnitude (V) | 19.008[1] |
| Characteristics | |
| Evolutionary stage | either a red supergiant or a foreground giant[2] |
| Spectral type | M3Ia[3] or M6+ III[4] |
| Apparent magnitude (B) | 22.8[citation needed] |
| Apparent magnitude (R) | 13.634[1] |
| Apparent magnitude (G) | 11.259[5] |
| Apparent magnitude (J) | 5.075[6] |
| Apparent magnitude (H) | 3.01[6] |
| Apparent magnitude (K) | 2.18[6] |
| Astrometry | |
| Proper motion (μ) | RA: -3.09±0.15[5] mas/yr Dec.: -4.12±0.12[5] mas/yr |
| Parallax (π) | 0.3370 ± 0.1235 mas[5] |
| Distance | 3,000[7] or 623[8] pc |
| Absolute magnitude (MV) | –6.96[9] |
| Details | |
| if a supergiant | |
| Radius | 1,241±70[9] R☉ |
| Luminosity | 219,000±26,000[9] L☉ |
| Temperature | 3,550[9] - 3,605[8] K |
| Age | 7.9[9] Myr |
| if a foreground giant | |
| Radius | 216[8] R☉ |
| Luminosity | 1,000[2]or7,178 – 7,379[8] L☉ |
| Temperature | 3,605[8] K |
| Other designations | |
Westerlund 1 W237, Westerlund 1 BKS B, 2MASS J16470309-4552189, Gaia EDR3 5940105904023386752 | |
| Database references | |
| SIMBAD | data |
Westerlund 1 W237, also known as Wd 1-237orWesterlund 1 BKS B, is a possible red supergiant (RSG) in the constellationofAra. It is one out of four known red supergiants in the Westerlund 1 super star cluster. As a red supergiant, it would be one of the largest known stars and one of the most luminous of its type.[7]
Westerlund 1 W237 is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.[10] It is surrounded by a radio nebula which is similar in mass to those of Westerlund 1-20 and Westerlund 1 W26, 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 (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 0.07 M☉ 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 2×10−5 M☉ per year.[11]
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 219,000 L☉, the radius of Westerlund 1 W237 would be 1,241 times the solar radius (R☉), making it larger than the orbit of Jupiter. The initial mass of W237 has been calculated from its position relative to theoretical stellar evolutionary tracks to be around 28 M☉ or 32 M☉ for a non-rotating star.[9]
The distance of Westerlund 1 W237 is assumed to be around 8,500+2,000
−1,300 light yearsor2,600+600
−400 parsecs[12] 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).[11] Another but older source suggests a similar distance of 3,000±500 parsecs.[7]
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 1,000 L☉.[2] Gaia Data Release 2 gives a parallax of 1.64±0.2608 mas for W237, implying a distance of 623+139
−96 pc and a luminosity of 7,178–7,379 L☉ with a corresponding radius of 216 R☉.[13][8] In 2020, the parallax was revised to the much smaller value of 0.3370±0.1235 mas, corresponding to a distance of 2967±1087 pc (9670±3540 ly).[5]
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