Westerlund 1 W237

Westerlund 1 W237
Westerlund 1 super star cluster (north is towards top left). The location of Wd 1-237 is circled.
Credit: ESO
Observation data
Epoch J2000      Equinox J2000
Constellation Ara
Right ascension 16h 47m 03.1075s
Declination −45° 52′ 18.957″
Apparent magnitude (V) 19.008
Characteristics
Evolutionary stage Either a red supergiant or a foreground giant
Spectral type M3Ia or M6+ III
Apparent magnitude (R) 13.634
Apparent magnitude (G) 11.259
Apparent magnitude (J) 5.075
Apparent magnitude (H) 3.01
Apparent magnitude (K) 2.18
Astrometry
Proper motion (μ) RA: −3.09±0.15 mas/yr
Dec.: −4.12±0.12 mas/yr
Parallax (π)0.3370±0.1235 mas
Distance3,000 pc
Absolute magnitude (MV)−6.96
Details
Radius1,241±70 R☉
Luminosity219,000±26,000 L☉
Temperature3,550 - 3,605 K
Age7.9 Myr
Other designations
Westerlund 1 W237, Westerlund 1 BKS B, 2MASS J16470309-4552189, Gaia DR3 5940105904023386752
Database references
SIMBADdata

Westerlund 1 W237 (commonly abbreviated to W237), also known as Westerlund 1 BKS B, is a red supergiant (RSG) in the constellation of Ara. It is one out of four known red supergiants in the Westerlund 1 super star cluster and one of the largest known stars and one of the most luminous of its type.

Physical characteristics

Westerlund 1 W237 compared to the other 3 RSGs (Red Supergiants) in the Westerlund 1 star cluster.

Westerlund 1 W237 is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum. 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.

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.

Distance

The distance of Westerlund 1 W237 is assumed to be around 8,500+2,000
−1,300 light years or 2,600+600
−400 parsecs 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 3,000±500 parsecs.

Westerlund's 1987 analysis assigned a spectral type of M6+ III to W237 and considered it to be a foreground giant with a luminosity only around 1,000 L☉. 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☉. In 2020, Gaia DR3 revised the parallax to the much smaller value of 0.3370±0.1235 mas , corresponding to a distance of 2,967±1,087 pc (9,670±3,540 ly). Both Gaia results carry significant statistical margin of error, as well as indicators that the astrometric excess noise is far beyond acceptable levels so that the parallax estimates should be considered unreliable.

See also

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. 1 2 3 4 5 6 7 8 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. 1 2 Bonanos, Alceste Z. (2007). "Variability of Young Massive Stars in the Galactic Super Star Cluster Westerlund 1". The Astronomical Journal. 133 (6): 2696–2708. arXiv:astro-ph/0702614. Bibcode:2007AJ....133.2696B. doi:10.1086/518093. S2CID 119074868.
  4. 1 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. Bibcode:1987A&AS...70..311W. ISSN 0365-0138.
  5. ↑ Clark, J. S.; Ritchie, B. W.; Negueruela, I. (2010). "A serendipitous survey for variability amongst the massive stellar population of Westerlund 1". Astronomy and Astrophysics. 514: A87. arXiv:1003.5107. Bibcode:2010A&A...514A..87C. doi:10.1051/0004-6361/200913820. S2CID 14780809.
  6. ↑ Bonanos, Alceste Z. (2007). "Variability of Young Massive Stars in the Galactic Super Star Cluster Westerlund 1". The Astronomical Journal. 133 (6): 2696–2708. arXiv:astro-ph/0702614. Bibcode:2007AJ....133.2696B. doi:10.1086/518093. S2CID 119074868.
  7. 1 2 3 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
  8. 1 2 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. arXiv:1209.6427. Bibcode:2012ApJ...760...65F. doi:10.1088/0004-637X/760/1/65. S2CID 53393926.
  9. 1 2 3 4 5 6 Arévalo, Aura (2019). The Red Supergiants in the Supermassive Stellar Cluster Westerlund 1 (Thesis). doi:10.11606/D.14.2019.tde-12092018-161841.
  10. 1 2 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. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  11. ↑ "Cl* Westerlund 1 W 237". Simbad.
  12. 1 2 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". Astronomy & Astrophysics. 511: A58. arXiv:0912.4165. Bibcode:2010A&A...511A..58D. doi:10.1051/0004-6361/200913505. ISSN 0004-6361. S2CID 9792700.
  13. ↑ Aghakhanloo, Mojgan; Murphy, Jeremiah W.; Smith, Nathan; Parejko, John; Díaz-Rodríguez, Mariangelly; Drout, Maria R.; Groh, Jose H.; Guzman, Joseph; Stassun, Keivan G. (2020-02-21). "Inferring the parallax of Westerlund 1 from Gaia DR2". Monthly Notices of the Royal Astronomical Society. 492 (2): 2497–2509. arXiv:1901.06582. Bibcode:2020MNRAS.492.2497A. doi:10.1093/mnras/stz3628. ISSN 0035-8711. S2CID 119465620.
  14. ↑ 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. arXiv:1804.10121. Bibcode:2018AJ....156...58B. doi:10.3847/1538-3881/aacb21. S2CID 119289017.