WR 20a

WR 20a
	WR 20a (circled) near Westerlund 2; Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
Observation data; Epoch J2000 Equinox J2000
Constellation	Carina
Right ascension	10h 23m 58.002s[1]
Declination	−57° 45′ 48.99″[1]
Apparent magnitude (V)	13.28[2]
Characteristics
Evolutionary stage	Hot slash star[3]
Spectral type	O3If/WN6 + O3If/WN6[4]
U−B color index	+0.29[2]
B−V color index	+1.63[2]
Variable type	β Lyr + WR[5]
Astrometry
Distance	25000[2] ly ; (7900 ± 600 pc)
Absolute magnitude (MV)	−6.49 + −6.49[2]
Orbit[6]
Period (P)	3.675 days
Semi-major axis (a)	26 R☉
Eccentricity (e)	0
Semi-amplitude (K1); (primary)	353.1 km/s
Semi-amplitude (K2); (secondary)	362.6 km/s
Details[2]
Mass	82.7 ± 5.5 M☉
Radius	19.3 ± 0.5 R☉
Luminosity	1,150,000 ± 150,000 L☉
Surface gravity (log g)	3.8 cgs
Temperature	43000 ± 2000 K
Mass	81.9 ± 5.5 M☉
Radius	19.3 ± 0.5 R☉
Luminosity	1,150,000 ± 150,000 L☉
Surface gravity (log g)	3.8 cgs
Temperature	43000 ± 2000 K
Other designations
	V712 Carinae, GEN#+4.38020004, THA 35-II-36, Westerlund 2 MSP 240, 2MASS J10235800-5745489, UBV M 40466, Westerlund 2 4
Database references
SIMBAD	data

WR20a is a binary star associated with the young, massive cluster Westerlund 2. It was discovered in 2004 to be one of the most massive binary systems known, for which the masses of the components have been accurately measured.[6]

Each star in the system has about eighty times the mass of the Sun.[6][7] It is not clear why this system is located away from the center of the cluster. It is possible that the system was formed in the core, but that it was ejected by dynamical interactions.

Every 3.6 days the two stars in this system revolve around each other. Although the stars are in very tight orbit, both stars in the system are detached.[8]

It is expected that within a million years the two will expand and come into contact. A large nitrogen abundance has been measured on the surface of the stars,[2] about six times the abundance of nitrogen measured in the sun. This nitrogen is probably produced in deeper layers of the star and pushed towards the surface by rotational mixing.

A collision between the two winds of the systems has been detected in the visible as well as in X-rays.[2][9] The X-ray emitting region is quite extended since it does not suffer from any eclipse.

References

Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally Published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.
Rauw; et al. (4 March 2005). "The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions" (PDF). Astronomy & Astrophysics. 432 (3): 985–998. Bibcode:2005A&A...432..985R. doi:10.1051/0004-6361:20042136.
Crowther, Paul A.; Walborn, Nolan R. (2011). "Spectral classification of O2-3.5 If*/WN5-7 stars". Monthly Notices of the Royal Astronomical Society. 416 (2): 1311. arXiv:1105.4757. Bibcode:2011MNRAS.416.1311C. doi:10.1111/j.1365-2966.2011.19129.x.
Roman-Lopes, A. (2013). "An O2 If*/WN6 star caught in the act in a compact H II region in the starburst cluster NGC 3603". Monthly Notices of the Royal Astronomical Society. 433: 712. arXiv:1305.0851. Bibcode:2013MNRAS.433..712R. doi:10.1093/mnras/stt762.
Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
Rauw; et al. (3 June 2004). "WR20a: a massive cornerstone binary system comprising two extreme early-type stars". Astronomy & Astrophysics. 420 (2): L9–L13. arXiv:astro-ph/0404551. Bibcode:2004A&A...420L...9R. doi:10.1051/0004-6361:20040150.
Bonanos, A. Z.; Stanek, K. Z.; Udalski, A.; Wyrzykowski, L.; Żebruń, K.; Kubiak, M.; Szymański, M. K.; Szewczyk, O.; Pietrzyński, G.; Soszyński, I. (2004). "WR 20a is an Eclipsing Binary: Accurate Determination of Parameters for an Extremely Massive Wolf-Rayet System". The Astrophysical Journal. 611: L33. arXiv:astro-ph/0405338. Bibcode:2004ApJ...611L..33B. doi:10.1086/423671.
Rauw; et al. (1 March 2007). "Early-type stars in the core of the young open cluster Westerlund 2". Astronomy & Astrophysics. 463 (3): 981–991. arXiv:astro-ph/0612622. Bibcode:2007A&A...463..981R. doi:10.1051/0004-6361:20066495.
Naze; et al. (1 May 2008). "Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund 2". Astronomy & Astrophysics. 483 (1): 171–182. arXiv:0801.0647. Bibcode:2008A&A...483..171N. doi:10.1051/0004-6361:20078851.

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[2mass-1] Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally Published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C.

[Rauw2005-2] Rauw; et al. (4 March 2005). "The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions" (PDF). Astronomy & Astrophysics. 432 (3): 985–998. Bibcode:2005A&A...432..985R. doi:10.1051/0004-6361:20042136.

[crowther-3] Crowther, Paul A.; Walborn, Nolan R. (2011). "Spectral classification of O2-3.5 If*/WN5-7 stars". Monthly Notices of the Royal Astronomical Society. 416 (2): 1311. arXiv:1105.4757. Bibcode:2011MNRAS.416.1311C. doi:10.1111/j.1365-2966.2011.19129.x.

[roman-4] Roman-Lopes, A. (2013). "An O2 If*/WN6 star caught in the act in a compact H II region in the starburst cluster NGC 3603". Monthly Notices of the Royal Astronomical Society. 433: 712. arXiv:1305.0851. Bibcode:2013MNRAS.433..712R. doi:10.1093/mnras/stt762.

[gcvs-5] Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.

[Rauw2004-6] Rauw; et al. (3 June 2004). "WR20a: a massive cornerstone binary system comprising two extreme early-type stars". Astronomy & Astrophysics. 420 (2): L9–L13. arXiv:astro-ph/0404551. Bibcode:2004A&A...420L...9R. doi:10.1051/0004-6361:20040150.

[7] Bonanos, A. Z.; Stanek, K. Z.; Udalski, A.; Wyrzykowski, L.; Żebruń, K.; Kubiak, M.; Szymański, M. K.; Szewczyk, O.; Pietrzyński, G.; Soszyński, I. (2004). "WR 20a is an Eclipsing Binary: Accurate Determination of Parameters for an Extremely Massive Wolf-Rayet System". The Astrophysical Journal. 611: L33. arXiv:astro-ph/0405338. Bibcode:2004ApJ...611L..33B. doi:10.1086/423671.

[8] Rauw; et al. (1 March 2007). "Early-type stars in the core of the young open cluster Westerlund 2". Astronomy & Astrophysics. 463 (3): 981–991. arXiv:astro-ph/0612622. Bibcode:2007A&A...463..981R. doi:10.1051/0004-6361:20066495.

[9] Naze; et al. (1 May 2008). "Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund 2". Astronomy & Astrophysics. 483 (1): 171–182. arXiv:0801.0647. Bibcode:2008A&A...483..171N. doi:10.1051/0004-6361:20078851.