WR 147

WR 147 is a star system in the constellation of Cygnus. Its distance has been calculated to be around 2,100 ± 200 light years (630 ± 70 parsecs) away from the Earth. This puts the star in front of the OB association known as Cygnus OB2.[3] The system is extremely reddened by interstellar extinction - that is, dust in front of the star scatters much of the blue light coming from WR 147, leaving the star appearing reddish.

WR 147
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  20h 36m 43.636s[1]
Declination +40° 21′ 07.69″[1]
Apparent magnitude (V) 13.86 + 16.02[2]
Characteristics
WR
Evolutionary stage Wolf-Rayet star
Spectral type WN8h[1]
B−V color index +4.06
OB
Spectral type B0.5V[1]
B−V color index +4.09
Astrometry
Distance2,100 ± 200 ly
(630 ± 70[3] pc)
Absolute magnitude (MV)−7.22[4]
Details
WR 147S (WR)
Mass51[4] M☉
Radius29.8[4] R☉
Luminosity2,000,000[4] L☉
Temperature39,800[4] K
WR 147N (OB)
Radius9.18 R☉
Luminosity50,000[5] L☉
Temperature28,500[5] K
Other designations
IRAS 20349+4010, 1E 2034+40.1, 2E 4394, 2MASS J20364364+4021075
Database references
SIMBADWR 147
WR 147N

Distance

The distance of WR 147 has been calculated to be 630 parsecs (pc) based on infrared photometry. The extinction in the visual range was calculated to be 11.5 magnitudes and the absolute visual magnitude assumed to be −6.7.[3] This would make WR 147 one of the closest known Wolf-Rayet stars, despite its faint apparent magnitude.[2][4]

A later calculation using optical and ultraviolet photometry derived a slightly lower value for the extinction. Combined with an assumption of a brighter absolute magnitude, this gave a distance modulus of 10.6 corresponding to a distance of about 1,200 pc. This is still one of the nearest Wolf-Rayet systems to the sun.[4]

System

WR 147 consists of two very massive stars, a Wolf-Rayet star, designated WR 147S, and another companion, designated WR 147N, which is a B-type main-sequence star (although it may also be an O-type giant).[6]

WR 147 was resolved into two components in the 1990s,[5] separated first at radio wavelengths.[3] Based on an angular separation of about 643 ± 157 mas,[5] this translates to an projected (i.e. minimum) separation of about 403 ± 45 AU, which is about thirteen times the distance between Neptune and the Sun.[7] The location of the companion resolved in the near-infrared is slightly further from the primary than the radio source originally called WR 147N, and it has been referred to as WR 147NIR.[8]

The Wolf-Rayet star in the system (WR 147S) has a luminosity of 2,000,000 L☉, making it one of the most luminous stars known. The B-type companion is much less luminous, at 50,000 L☉.

The orbital elements of WR 147's orbit are poorly known, as the two components are separated far enough that no orbital motion has been detected. The inclination of WR 147's orbit to our line of sight is also unknown: numerous studies have given values ranging from 30° to 60°.[5] Constraining the value of the inclination is important because the true separation of the stars depends on the value.[5]

Colliding wind

Stellar wind from these two stars collide and emit X-rays and radio waves. The Wolf-Rayet star is losing mass at a rate of 2.4×10−5 M☉/yr and the companion is losing mass at a rate of 4×10−7 M☉/yr.[5] The plasma generated from the wind collision may reach temperatures as high as 2.7 keV, or 31 million kelvins.[7]

Despite the name, the colliding wind shock is actually considered to be collisionless, that is the ions in the wind do not for the most part directly collide.[1]

X-rays

In 2010, X-ray emission from WR 147 was resolved into two sources: one where the wind collision is thought to be occurring, and another directly from the Wolf-Rayet star, the cause of which is not clear.[1] It was hypothesized to be another massive star orbiting the Wolf-Rayet star; if so, it would have an orbital period of 15 to 20 days, with the total mass of the system being 20 M☉, leading to a separation of about 0.33 AU.[9]

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See also
  • WR 140, the prototype colliding-wind binary

References
  1. Zhekov, S. A.; Park, S. (2010). "Chandra Observations of WR 147 Reveal a Double X-ray Source". The Astrophysical Journal Letters. 709 (2): L119–L123. arXiv:0912.3554. Bibcode:2010ApJ...709L.119Z. doi:10.1088/2041-8205/709/2/L119.
  2. Niemela, Virpi S.; Shara, Michael M.; Wallace, Debra J.; Zurek, David R.; Moffat, Anthony F. J. (1998). "Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed". The Astronomical Journal. 115 (5): 2047. Bibcode:1998AJ....115.2047N. doi:10.1086/300320.
  3. Churchwell, E.; Bieging, J. H.; van der Hucht, K. A.; Williams, P. M.; Spoelstra, T. A. Th.; Abbott, D. C. (1992). "The Wolf-Rayet system WR 147 - A binary radio source with thermal and nonthermal components". Astrophysical Journal, Part 1. 393 (1): 329–340. Bibcode:1992ApJ...393..329C. doi:10.1086/171508.
  4. Hamann, W.-R.; Gräfener, G.; Liermann, A. (2006). "The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation". Astronomy and Astrophysics. 457 (3): 1015–1031. arXiv:astro-ph/0608078. Bibcode:2006A&A...457.1015H. doi:10.1051/0004-6361:20065052.
  5. Reimer, A.; Reimer, O. (2009). "Parameter Constraints for High-Energy Models of Colliding Winds of Massive Stars: The Case WR 147". The Astrophysical Journal. 694 (2): 1139–1146. arXiv:0901.1297. Bibcode:2009ApJ...694.1139R. doi:10.1088/0004-637X/694/2/1139.
  6. Zhekov, S. A. (2007). "Colliding stellar wind models with non-equilibrium ionization: X-rays from WR 147". Monthly Notices of the Royal Astronomical Society. 382 (2): 886–894. arXiv:0709.1686. Bibcode:2007MNRAS.382..886Z. doi:10.1111/j.1365-2966.2007.12450.x.
  7. Skinner, S. L.; Zhekov, S. A.; Güdel, M.; Schmutz, W. (2007). "XMM-Newton X-ray observations of the Wolf-Rayet binary system WR 147". Monthly Notices of the Royal Astronomical Society. 378 (4): 1491–1498. arXiv:0704.3235. Bibcode:2007MNRAS.378.1491S. doi:10.1111/j.1365-2966.2007.11892.x.
  8. Williams, P. M.; Dougherty, S. M.; Davis, R. J.; Van Der Hucht, K. A.; Bode, M. F.; Setia Gunawan, D. Y. A. (1997). "Radio and infrared structure of the colliding-wind Wolf-Rayet system WR147". Monthly Notices of the Royal Astronomical Society. 289: 10. Bibcode:1997MNRAS.289...10W. CiteSeerX 10.1.1.23.1193. doi:10.1093/mnras/289.1.10.
  9. Zhekov, S. A.; Park, S. (2010). "Chandra HETG Observations of the Colliding Stellar Wind System WR 147". The Astrophysical Journal. 721 (1): 518–529. arXiv:1007.4352. Bibcode:2010ApJ...721..518Z. doi:10.1088/0004-637X/721/1/518.
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