Astronomy:Westerlund 1-237

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Coordinates: Sky map 16h 47m 03.11s, −45° 52′ 19.0″

Westerlund 1-237
Surprise Cloud Around Vast Star.jpg
Red circle.svg
Westerlund 1 super star cluster. The location of Wd 1-237 is circled.
Credit: ESO
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara
Right ascension  16h 47m 03.11s[1]
Declination −45° 52′ 19.0″[1]
Apparent magnitude (V) 19.008
Evolutionary stage either a red supergiant or a foreground giant[2]
Spectral type M3Ia
Apparent magnitude (B) 22.8
Apparent magnitude (J) 5.075
Apparent magnitude (H) 3.01
Apparent magnitude (K) 2.18
Apparent magnitude (G) 11.3245
Apparent magnitude (R) 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
Distance3,000±500[3] pc
Radius216[4] - 1,245[3] R
Luminosity7,178[4] - 234,000[3] L
Temperature3,600[3] - 3,605[4] K
Other designations
Westerlund 1 W237, Westerlund 1 BKS B, 2MASS J16470309-4552189
Database references

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]


The distance of Westerlund 1 is assumed to be around 8,500+2,000
 light years
or 2,600+600
[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
and a luminosity of 7,178–7,379 L with a corresponding radius of 216 R.[9][4]

See also


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


  1. 1.0 1.1 1.2 1.3 1.4 1.5 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. 2.0 2.1 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. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 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. 4.0 4.1 4.2 4.3 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. "APOD: 2017 June 20 - The Massive Stars in Westerlund 1". 
  6. "Cl* Westerlund 1 W 237".*+Westerlund+1+W+237. 
  7. 7.0 7.1 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. 
  8. 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. 
  9. 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.