# Astronomy:Westerlund 1-237

Observation dataEquinox J2000.0]] (ICRS) Constellation Westerlund 1 super star cluster. The location of Wd 1-237 is circled.Credit: ESO Ara 16h 47m 03.11s[1] −45° 52′ 19.0″[1] 19.008 either a red supergiant or a foreground giant[2] M3Ia 22.8 5.075 3.01 2.18 11.3245 13.634 Proper motion (μ) RA: -4.379[1] mas/yr Dec.: -1.555[1] mas/yr Parallax (π) 1.6415 ± 0.2608[1] mas Distance 3,000±500[3] pc Radius 216[4] - 1,245[3] R☉ Luminosity 7,178[4] - 234,000[3] L☉ Temperature 3,600[3] - 3,605[4] K Westerlund 1 W237, Westerlund 1 BKS B, 2MASS J16470309-4552189 SIMBAD data

Westerlund 1-237 or Wd 1-237 is a possible red supergiant (RSG) 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.[5] As a red supergiant, it would be one of the largest known stars.[3]

## Physical characteristics

Westerlund 1-237 compared to the other 3 RSGs (Red Supergiants) in the Westerlund 1 star cluster.

Westerlund 1-237 is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.[6] 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 (W20 and W26 have pronounced cometary shaped nebula). 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.[7]

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 234,000 L, the radius of Westerlund 1-237 would be 1,245 times the solar radius (R), 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.[3][lower-alpha 1]

## Distance

The distance of Westerlund 1 is assumed to be around 8,500+2,000
−1,300
light years
or 2,600+600
−400
parsecs
[8] 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).[7] Another source suggests a similar distance of 3,000±500 parsecs.[3]

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 1,000 L.[2] Gaia Data Release 2 gives a parallax of 1.64±0.2608 mas for W1-237,[1] implying a distance of 623+139
−96
pc
and a luminosity of 7,178–7,379 L with a corresponding radius of 216 R.[9][4]

## Notes

1. $\displaystyle{ \sqrt{\left(\frac{5772}{3600}\right)^4\cdot 10^{5.37}}\approx1244.65 \ R_\odot }$

## References

1. Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
2. Westerlund, B. E. (1987). "Photometry and spectroscopy of stars in the region of a highly reddened cluster in ARA". Astronomy and Astrophysics. Supplement 70 (3): 311–324. ISSN 0365-0138. Bibcode1987A&AS...70..311W.
3. Fok, Thomas K. T.; Nakashima, Jun-Ichi; Yung, Bosco H. K.; Hsia, Chih-Hao; Deguchi, Shuji (2012). "Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters". The Astrophysical Journal 760 (1): 65. doi:10.1088/0004-637X/760/1/65. Bibcode2012ApJ...760...65F.
4. Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal 158 (1): 20. doi:10.3847/1538-3881/ab1cbd. Bibcode2019AJ....158...20M.
5. Dougherty, S. M.; Clark, J. S.; Negueruela, I.; Johnson, T.; Chapman, J. M. (2010-02-01). "Radio emission from the massive stars in the galactic super star cluster Westerlund 1" (in en). Astronomy & Astrophysics 511: A58. doi:10.1051/0004-6361/200913505. ISSN 0004-6361. Bibcode2010A&A...511A..58D.
6. Aghakhanloo, Mojgan; Murphy, Jeremiah W.; Smith, Nathan; Parejko, John; Díaz-Rodríguez, Mariangelly; Drout, Maria R.; Groh, Jose H.; Guzman, Joseph et al. (2020-02-21). "Inferring the parallax of Westerlund 1 from Gaia DR2". Monthly Notices of the Royal Astronomical Society 492 (2): 2497–2509. doi:10.1093/mnras/stz3628. ISSN 0035-8711. Bibcode2020MNRAS.492.2497A.
7. Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Mantelet, G.; Andrae, R. (2018). "Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2". The Astronomical Journal 156 (2): 58. doi:10.3847/1538-3881/aacb21. Bibcode2018AJ....156...58B.