Westerlund 1-20

Westerlund 1-20
	Westerlund 1 super star cluster. The location of Wd 1-20 is circled.; Credit: ESO
Observation data; Epoch J2000 Equinox J2000
Constellation	Ara
Right ascension	16h 47m 04.69s
Declination	−45° 51′ 23.9″
Characteristics
Evolutionary stage	Red supergiant
Spectral type	M3 - M6I
Apparent magnitude (J)	6.378
Apparent magnitude (H)	4.381
Apparent magnitude (K)	2.61
Astrometry
Proper motion (μ)	RA: -2.478 mas/yr ; Dec.: -4.041 mas/yr
Parallax (π)	0.1690 ± 0.1073 mas
Distance	2,600+600; −400 (assumed) pc
Details
Radius	858±48 R☉
Luminosity	101,000±13,000 L☉
Temperature	3,284 - 3,550 K
Other designations
	Westerlund 1 W20, Westerlund 1 BKS D, 2MASS J16470468-4551238, Gaia EDR3 5940106007092341120
Database references
SIMBAD	data

Westerlund 1-20 or Wd 1-20 is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius was calculated to be around 965 solar radii^[1] (6.72 × 10⁸ km, 4.48 au), making it one of the largest stars discovered so far. This corresponds to a volume 899 million times bigger than the Sun. If placed at the center of the Solar System, the photosphere of Westerlund 1-20 would almost reach the orbit of Jupiter.

The star is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.^[6] W20 occupies the upper right corner of the Hertzsprung-Russell diagram. Using the effective temperature of 3,500 K,^[1] the bolometric luminosity of 126,000 L_☉^[1] and the solar effective temperature of 5,772 K,^[7] its radius can be calculated using the Stefan-Boltzmann law.^[a]

Westerlund 1-20 was observed to have an extended, cometary shaped nebula, similar to the other red supergiant Westerlund 1-26. It is therefore likely that its morphology was affected by either the intracluster medium or the cluster wind of Westerlund 1.^[8] The nebulae of both Westerlund 1-20 and Westerlund 1-26 are extended outward from the cluster core and most bright at inward direction, indicating the outward cluster wind.^[9]

Notes

^ ${\sqrt {\left({\frac {5772}{3500}}\right)^{4}\cdot 125893}}\approx 964.98\ R_{\odot }$

References

^ ^a ^b ^c ^d ^e 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.
^ ^a ^b ^c ^d Arévalo, Aura (2019). The Red Supergiants in the Supermassive Stellar Cluster Westerlund 1 (Thesis). doi:10.11606/D.14.2019.tde-12092018-161841.
^ Westerlund, B. E. (1987). "Photometry and spectroscopy of stars in the region of a highly reddened cluster in Ara". Astronomy and Astrophysics Supplement Series. 70: 311. Bibcode:1987A&AS...70..311W.
^ ^a ^b ^c Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
^ 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.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ "Cl* Westerlund 1 W 20". Simbad.
^ Williams, D. R. (2013). "Sun Fact Sheet".
^ 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.
^ Asymmetric Ejecta of Cool Supergiants and Hypergiants in the Massive Cluster Westerlund 1, 2018, arXiv:1803.07008

[radius-8] ${\sqrt {\left({\frac {5772}{3500}}\right)^{4}\cdot 125893}}\approx 964.98\ R_{\odot }$

[:0-1] 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.

[paulo2018-2] Arévalo, Aura (2019). The Red Supergiants in the Supermassive Stellar Cluster Westerlund 1 (Thesis). doi:10.11606/D.14.2019.tde-12092018-161841.

[westerlund1987-3] Westerlund, B. E. (1987). "Photometry and spectroscopy of stars in the region of a highly reddened cluster in Ara". Astronomy and Astrophysics Supplement Series. 70: 311. Bibcode:1987A&AS...70..311W.

[EDR3-4] Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.

[5] 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.{{cite journal}}: CS1 maint: unflagged free DOI (link)

[6] "Cl* Westerlund 1 W 20". Simbad.

[7] Williams, D. R. (2013). "Sun Fact Sheet".

[9] 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.

[10] Asymmetric Ejecta of Cool Supergiants and Hypergiants in the Massive Cluster Westerlund 1, 2018, arXiv:1803.07008

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See also

Notes

References