WR 21a

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WR 21a
Westerlund 2.jpg
Green circle.png
Location of WR 21a (circled) near RCW 49
Credit: ESO
Observation data
Epoch J2000      Equinox J2000
Constellation Carina
Right ascension 10h 25m 56.50s[1]
Declination −57° 48′ 43.5″[1]
Apparent magnitude (V) 12.661[2]
Characteristics
Spectral type O3/WN5ha + O3Vz((f*))[3]
B−V color index +1.507[2]
Astrometry
Proper motion (μ) RA: -4.079[4] mas/yr
Dec.: 2.617[4] mas/yr
Parallax (π)0.2497 ± 0.0143[4] mas
Distance13,100 ± 700 ly
(4,000 ± 200 pc)
Absolute magnitude (MV)−7.20[3]
Orbit[3]
PrimaryWR
CompanionO
Period (P)31.672 ± 0.011 days
Semi-major axis (a)230 R☉[5]
Eccentricity (e)0.6949 ± 0.0047
Inclination (i)58.8 ± 2.5°
Semi-amplitude (K1)
(primary)		156.9 ± 2.0 km/s
Semi-amplitude (K2)
(secondary)		278.6 ± 5.3 km/s
Details
WR
Mass103.6 ± 10.2[3] M☉
Radius12.0[5] R☉
Luminosity1,800,000[3] L☉
Temperature45,000[6] K
O
Mass58.3 ± 3.7[3] M☉
Radius13.84[5] R☉
Luminosity630,000[3] L☉
Temperature50,680[6] K
Age1.5[3] Myr
Other designations
WR 21a, 2MASS J10255650-5748435
Database references
SIMBADdata

WR 21a is a binary star in the constellation Carina. It includes one of the most massive known stars and is one of the most massive binaries.

WR 21a lies near the Westerlund 2 open cluster[7] and likely to be an ejected member.[8]

The distance of WR 21a was not definitely known until Gaia mission. There have been estimates from 2.85 kpc to around 8 kpc, with consequent uncertainties in the system luminosity. The larger distance was preferred because of consistency with the derived orbital parameters.[6][9]

Every 31 days and 16 hours the two stars in this system revolve around each other. The inclination of the orbit means that we do not see eclipses and the visual brightness of the system is quite stable.[3]

The colliding winds of the two stars produce extremely high temperatures and luminous x-ray emission.[5] The system is also bright at radio wavelengths.[6]

References[]

  1. ^ a b 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.
  2. ^ a b Zacharias, N.; Finch, C. T.; Girard, T. M.; Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I. (2013). "The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)". The Astronomical Journal. 145 (2): 44. arXiv:1212.6182. Bibcode:2013AJ....145...44Z. doi:10.1088/0004-6256/145/2/44. S2CID 119299381.
  3. ^ a b c d e f g h i Tramper, F.; Sana, H.; Fitzsimons, N. E.; De Koter, A.; Kaper, L.; Mahy, L.; Moffat, A. (2016). "The mass of the very massive binary WR21a". Monthly Notices of the Royal Astronomical Society. 455 (2): 1275–1281. arXiv:1510.03609. Bibcode:2016MNRAS.455.1275T. doi:10.1093/mnras/stv2373. S2CID 44364798.
  4. ^ 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. Gaia EDR3 record for this source at VizieR.
  5. ^ a b c d Gosset, Eric; Naze, Yael (2016). "The X-ray light curve of the massive colliding wind Wolf-Rayet + O binary WR21a". Astronomy & Astrophysics. 1604: A113. arXiv:1604.01536. Bibcode:2016A&A...590A.113G. doi:10.1051/0004-6361/201527051. S2CID 119183652.
  6. ^ a b c d Benaglia, P.; Romero, G. E.; Koribalski, B.; Pollock, A. M. T. (2005). "Multiwavelength studies of WR 21a and its surroundings". Astronomy and Astrophysics. 440 (2): 743–750. arXiv:astro-ph/0506363. Bibcode:2005A&A...440..743B. doi:10.1051/0004-6361:20042617. S2CID 17048378.
  7. ^ Hur, Hyeonoh; Park, Byeong-Gon; Sung, Hwankyung; Bessell, Michael S.; Lim, Beomdu; Chun, Moo-Young; Sohn, Sangmo Tony (2015). "Reddening, distance, and stellar content of the young open cluster Westerlund 2". Monthly Notices of the Royal Astronomical Society. 446 (4): 3797–3819. arXiv:1411.0879. Bibcode:2015MNRAS.446.3797H. doi:10.1093/mnras/stu2329. S2CID 119221719.
  8. ^ The Villafranca catalog of Galactic OB groups: I. Systems with O2-O3.5 stars, 2020, arXiv:2009.05773
  9. ^ Carraro, G.; Turner, D.; Majaess, D.; Baume, G. (2013). "The distance to the young open cluster Westerlund 2". Astronomy & Astrophysics. 555: A50. arXiv:1305.4309. Bibcode:2013A&A...555A..50C. doi:10.1051/0004-6361/201321421. S2CID 53756444.
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