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 56.502s [1]
Declination −57° 48′ 43.52″ [1]
Apparent magnitude  (V)12.661 [2]
Characteristics
Spectral type O3/WN5ha + O3Vz((f*)) [3]
B−V color index +1.507 [2]
Variable type Eclipsing [4]
Astrometry
Proper motion (μ)RA: −4.079 [1]   mas/yr
Dec.: 2.617 [1]   mas/yr
Parallax (π)0.2497 ± 0.0143  mas [1]
Distance 13,100 ± 700  ly
(4,000 ± 200  pc)
Absolute magnitude  (MV)−7.20 [3]
Orbit [4]
PrimaryWR
CompanionO
Period (P)31.67855±0.00002 days
Semi-major axis (a)230 R☉ [5]
Eccentricity (e)0.695±0.007
Inclination (i)61.8±1.5°
Semi-amplitude (K1)
(primary)		158.0±2.7 km/s
Semi-amplitude (K2)
(secondary)		278.1±2.8 km/s
Details
WR
Mass 94.4 [4]   M☉
Radius 23.3±1.6 [4]   R☉
Luminosity 1,510,000 [4]   L☉
Surface gravity (log g)3.69 [4]   cgs
Temperature 45,000 [6]   K
O
Mass 53.6 [4]   M☉
Radius 14.8±2.0 [4]   R☉
Luminosity1,050,000 [4]   L☉
Surface gravity (log g)3.81 [4]   cgs
Temperature 50,680 [6]   K
Age 1.5 [3]   Myr
Other designations
WR  21a, 2MASS  J10255650-5748435
Database references
SIMBAD data

WR 21a is an eclipsing 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 definitively 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 only very shallow eclipses are observed and the brightness dips by only about 0.05 magnitudes. There are also even smaller brightness variations attributed to the heartbeat effect where the closest passage of the stars in their eccentric orbits creates brightness changes as the two stars illuminate each other. There may also be tidally-excited oscillations producing further small variations. [4]

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]

Related Research Articles

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<span class="mw-page-title-main">WR 20a</span> Star in the constellation Carina

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<span class="mw-page-title-main">HD 151932</span> Star in the constellation of Scorpius

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<span class="mw-page-title-main">Westerlund 1-20</span> Red supergiant located in the Westerlund 1 super star cluster

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<span class="mw-page-title-main">DH Cephei</span> Binary star system in the constellation Cepheus

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<span class="mw-page-title-main">CV Serpentis</span>

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<span class="mw-page-title-main">RS Sagittarii</span> Eclipsing binary star system in the constellation Sagittarius

RS Sagittarii is an eclipsing binary star system in the southern constellation of Sagittarius, abbreviated RS Sgr. It is a double-lined spectroscopic binary with an orbital period of 2.416 days, indicating that the components are too close to each other to be individually resolved. The system has a combined apparent visual magnitude of 6.01, which is bright enough to be faintly visible to the naked eye. During the primary eclipse the brightness drops to magnitude 6.97, while the secondary eclipse is of magnitude 6.28. The distance to this system is approximately 1,420 light years based on parallax measurements.

References

  1. 1 2 3 4 5 Vallenari, A.; et al. (Gaia Collaboration) (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics . arXiv: 2208.00211 . doi: 10.1051/0004-6361/202243940 . Gaia DR3 record for this source at VizieR.
  2. 1 2 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. 1 2 3 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. 1 2 3 4 5 6 7 8 9 10 11 Barbá, Rodolfo H.; Gamen, Roberto C.; Martín-Ravelo, Pablo; Arias, Julia I.; Morrell, Nidia I. (2022). "The winking eye of a very massive star: WR 21a revealed as an eclipsing binary by TESS". Monthly Notices of the Royal Astronomical Society. 516 (1): 1149. arXiv: 2109.06311 . Bibcode:2022MNRAS.516.1149B. doi:10.1093/mnras/stac2173.
  5. 1 2 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. 1 2 3 4 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. ↑ Maíz Apellániz, J.; Crespo Bellido, P.; Barbá, R. H.; Fernández Aranda, R.; Sota, A. (2020), "The Villafranca catalog of Galactic OB groups", Astronomy & Astrophysics, 643: A138, arXiv: 2009.05773 , doi:10.1051/0004-6361/202038228, S2CID   221655188
  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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