Astronomy:WR 140

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Short description: Star in the constellation of Cygnus
WR 140
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This July 2022 image by the James Webb Space Telescope's Mid-Infrared Instrument shows WR 140 and its nebula.
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cygnus[1]
Right ascension  20h 20m 27.97608s[2]
Declination +43° 51′ 16.2802″[2]
Apparent magnitude (V) 6.85[3]
Characteristics
Spectral type WC7pd + O5.5fc[4]
Apparent magnitude (J) 5.547[5]
Apparent magnitude (K) 5.037[6]
U−B color index −0.35[3]
B−V color index +0.40[3]
Variable type WR[7]
Astrometry
Radial velocity (Rv)3.10[8] km/s
Proper motion (μ) RA: −4.275±0.027[9] mas/yr
Dec.: −1.874±0.026[9] mas/yr
Parallax (π)0.5378 ± 0.0237[9] mas
Distance1,518±21[10] pc
Absolute magnitude (MV)WR: −6.6 to −4.8
O: −6.11 to −5.94[11]
Orbit[10]
PrimaryO
CompanionWR
Period (P)2,895.00±0.29 d
Semi-major axis (a)8.922±0.067"
(13.55±0.21 au)
Eccentricity (e)0.8993±0.0013
Inclination (i)119.07±0.88°
Longitude of the node (Ω)353.87±0.67°
Periastron epoch (T)MJD 60,636.23±0.53
Argument of periastron (ω)
(secondary)		227.44±0.52°
Semi-amplitude (K1)
(primary)		26.50±0.48 km/s
Semi-amplitude (K2)
(secondary)		−75.25±0.63 km/s
Details
WR
Mass10.31±0.45[10] M☉
Luminosity537,000[12] L☉
Temperature70,000[12] K
O
Mass29.27±1.14[10] M☉
Radius35[12] R☉
Luminosity1.6 million[12] L☉
Temperature35,000[12] K
Other designations
V1687 Cygni, BD+43°3571, HD 193793, HIP 100287, TYC 3164-1678-1, SBC9 1232, WDS J20205+4351, 2MASS J20202798+4351164
Database references
SIMBADdata

WR 140 is a spectroscopic binary containing an O-type star and a Wolf-Rayet.[8] It is located in the constellation of Cygnus, lying in the sky at the centre of the triangle formed by Deneb, γ Cygni and δ Cygni.

Significance

WR 140 is thought to be a prototypical example of cosmic dust production.[13] In this mode of cosmic dust production, detritus enriched in silicon and carbon is periodically blown into the wider universe by certain stars toward the end of their lives. Such stars are termed Wolf–Rayets.

The outermost layers of a Wolf–Rayet star are enriched in oxygen, nitrogen, silicon and carbon. Indeed, the spectrographic presence of these elements, along with a notable absence of hydrogen, were one of the original diagnostic criteria for classifying a star as Wolf–Rayet. It is these enriched layers of the photosphere that are lost in repeating pulses. Once distant from the surface, the carbon fraction of this ejected material begins to glow at approximately 1,000 K. The heating is due to the star's UV radiation, the wavelength of its greatest luminosity. This has the effect of rebroadcasting the star's UV radiation in the infrared, which can be detected by suitable telescopes, such as the James Webb Space Telescope. The rebroadcast of the star's UV radiation by carbon and other metals traveling away from its surface creates the Doppler signature of a Wolf–Rayet—broad emission lines—rather than the far more common absorption-line spectra.

Binary system characteristics

An ultraviolet band light curve for V1687 Cygni, plotted from data published by Panov et al. (2000)[14]

WR 140 has been described as the brightest Wolf–Rayet star in the northern hemisphere, although WR 133 also in Cygnus is comparably bright.[4] Being less massive, less luminous, and probably less visually bright than its primary, the Wolf–Rayet component is often identified as the secondary star, despite the fact that it dominates the spectrum with its broad emission lines.[8][15] Or the components may be identified only as WR and O for clarity.[16] The primary star is an O4–5 star,[8] most likely a giant or supergiant.[11][12] Fahed et al. deduced a spectral type of O5.5fc, with a luminousity class between III and I.[4] This classification is commonly used for this star.[10][17]

The currently-accepted spectroscopic orbit is highly eccentric and has a period of 7.9±0.2 years, which has been determined from the velocity variations observed with the component's spectral lines, mostly from the Balmer absorption lines of the O4–5 primary and C IV emission lines at 465.0 nm for WR 140.[8] Separation between the two stars varies from 1.3 astronomical unit|AU at periastron to 23.9 AU at apastron.[12] WR 140 is listed as a Wolf–Rayet variable star whose visual brightness varies very slightly, and it has been given the variable star designation V1687 Cyg in the General Catalogue of Variable Stars.[7] Infrared light fluctuations during the orbit of WR 140 are studied because of its episodic dust formation. It is now regarded as the prototype colliding-wind binary.[11] Shortly after periastron passage every eight years, the infrared brightness increases dramatically and then slowly drops again over a period of months.[8] Here stellar winds collide with the dust formation created by the Wolf–Rayet star, causing the unusual bulges and angles in the concentric shells of dust.[11] The dust typically emitted by Wolf–Rayet systems is not so coherent or concentric as those of WR 140.


Dust shells

Model describing the dust formation around WR 140, figure published by Lau et al. 2023[18]

The dust shells around WR 140 were first observed in 1999/2001 with the Keck Observatory.[19] Ground-based infrared observations only resolved one to two discrete shells around the binary. Over 17 shells were observed with JWST MIRI, reaching out to about 45 arcseconds, or 70,000 astronomical units (AU). These represent more than 130 years of episodic dust production. A bright dust feature known as C1 has been used to analyse the mid-infrared spectrum of the shells; these shells show emission, probably due to polycyclic aromatic hydrocarbons (PAH), which is known to be highly stable. These features indicate hydrogen-poor and carbon-rich dust particles.[17]

Multi-epoch observations with Keck showed that the dust shells are accelerating under radiation pressure. When the grains first form at a distance of approximately 50 AU from the star they have a speed of 1,810+140
−170 km/s. They then experience an acceleration of 900+700
−400 km/s per year until they reach around 220 AU, the dust becomes optically thin and the acceleration decreases.[20] With the help of Subaru and Keck, the shells were detected in the mid- and near-infrared. The mid-infrared detection corresponds to colder (500 K) larger dust grains (30 to 50 nm) and the near-infrared detection corresponds to hotter (1,000 K) nano-sized dust (1 nm). These nano-sized dust grains exist in excess and are either produced by grain-grain collision or by radiative torque disruption (RATD).[18]

Mechanism of dust production

While interactions between the stellar winds of the two stars of WR 140 may be responsible for concentrating dust into discrete bands, it is not known how the concentric shells are formed. It is thought that nuclear processes in the Wolf–Rayet star may contribute an unusual degree of coherence to dust emissions.[21]

As the Wolf–Rayet star in WR 140 neared the end of its short life its core ran out of hydrogen to fuse into helium. With the loss of the radiation pressure this fusion provided, the balance that determines the radii of all stars shifted decisively towards gravitational collapse. The Wolf–Rayet star began to lose volume as its own gravitational contraction compacted its cooler interior. This collapse eventually began to slow as it grew more intense and heated the star's interior. Along the edge of the core a thin shell experienced temperatures and pressures sufficient to begin helium fusion. This helium burning provided a burst of radiation pressure that propagated through the star, up to its surface. The star began to inflate, though this increase in size was only temporary. The thin shell of helium fusion eventually caused enough expansion to moderate, or even extinguish its own reaction. The star once again began to collapse. However, at the surface this loss of internal radiation pressure had the effect of blowing the outermost layers of the star's photosphere into space. Following this, the star began to fuse helium at a greater rate and temporarily regained its former radiation pressure. This helium fusion once again stalled, and the subsequent gravitational collapse dislodged another layer of photosphere into space. These pulses will continue as long as this cycle of intermittent helium fusion can repeat itself.

The cast-off materials are essentially extremely large injections of cosmic dust into the star's stellar wind, which then carries it away from the star at several hundred kilometers per second. It is not well understood whether the unusual concentricity of WR 140's dust is due to interactions between the two stellar winds or is the result of nuclear processes in the Wolf–Rayet member itself.

The high surface temperature of Wolf–Rayet stars (up to 210,000 K) produces intense ultraviolet radiation, enough to make 20 or more layers of dust visible to instrumentation. The distance between the concentric shells of ejected material corresponds to the time between one faltering of the star's helium burning and another. This period is close to eight years, with new emissions having been observed in 1985, 1993, 2001 and 2009.[22] One estimate places the distance between shells at around 1.4 trillion km, meaning that if the Sun were such a Wolf–Rayet star one shell would be well into the Oort cloud and around 5% of the way to Alpha Centauri before another shell were cast off.[23] As seen in the JWST image at top right these intervals can be highly stable, continuing over many decades or hundreds of years.

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific 99 (617): 695. doi:10.1086/132034. Bibcode: 1987PASP...99..695R  Constellation record for this object at VizieR.
  2. ↑ 2.0 2.1 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  3. ↑ 3.0 3.1 3.2 Ducati, J. R. (2002). "VizieR On-line Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237. Bibcode: 2002yCat.2237....0D. 
  4. ↑ 4.0 4.1 4.2 Fahed, R.; Moffat, A. F. J.; Zorec, J.; Eversberg, T.; Chené, A. N.; Alves, F.; Arnold, W.; Bergmann, T. et al. (2011). "Spectroscopy of the archetype colliding-wind binary WR 140 during the 2009 January periastron passage". Monthly Notices of the Royal Astronomical Society 418 (1): 2–13. doi:10.1111/j.1365-2966.2011.19035.x. Bibcode: 2011MNRAS.418....2F. 
  5. ↑ Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E. et al. (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. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246. 
  6. ↑ Van Der Hucht, K. A. (2006). "New Galactic Wolf–Rayet stars, and candidates. An annex to the VIIth Catalogue of Galactic Wolf–Rayet Stars". Astronomy and Astrophysics 458 (2): 453–459. doi:10.1051/0004-6361:20065819. Bibcode: 2006A&A...458..453V. 
  7. ↑ 7.0 7.1 Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+, 2007-2017)". Vizier Online Data Catalog 1. Bibcode: 2009yCat....102025S. 
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G. et al. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics 424 (2): 727–732. doi:10.1051/0004-6361:20041213. Bibcode: 2004A&A...424..727P. 
  9. ↑ 9.0 9.1 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Thomas, Joshua D. et al. (2021). "The orbit and stellar masses of the archetype colliding-wind binary WR 140". Monthly Notices of the Royal Astronomical Society 504 (4): 5221–5230. doi:10.1093/mnras/stab1181. Bibcode: 2021MNRAS.504.5221T. 
  11. ↑ 11.0 11.1 11.2 11.3 Monnier, J. D.; Zhao, Ming; Pedretti, E.; Millan-Gabet, R.; Berger, J.-P.; Traub, W.; Schloerb, F. P.; Ten Brummelaar, T. et al. (2011). "First Visual Orbit for the Prototypical Colliding-wind Binary WR 140". The Astrophysical Journal Letters 742 (1): L1. doi:10.1088/2041-8205/742/1/L1. Bibcode: 2011ApJ...742L...1M. 
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 Williams, Peredur (2011). "Results from the 2009 campaign on WR 140". Bulletin de la Société Royale des Sciences de Liège 80: 595. Bibcode: 2011BSRSL..80..595W. 
  13. ↑ "WR140 Introduction". https://www.roe.ac.uk/~pmw/Wr140int.htm. 
  14. ↑ Panov, Kiril P.; Altmann, Martin; Seggewiss, Wilhelm (March 2000). "Long-term photometry of the Wolf-Rayet stars WR 137, WR 140, WR 148, and WR 153". Astronomy and Astrophysics 355: 607–616. Bibcode: 2000A&A...355..607P. 
  15. ↑ Lieb, Emma P.; Lau, Ryan M.; Hoffman, Jennifer L.; Corcoran, Michael F.; Garcia Marin, Macarena; Gull, Theodore R.; Hamaguchi, Kenji; Han, Yinuo et al. (2025). "Dynamic Imprints of Colliding-wind Dust Formation from WR 140". The Astrophysical Journal 979 (1): L3. doi:10.3847/2041-8213/ad9aa9. Bibcode: 2025ApJ...979L...3L. 
  16. ↑ Zhekov, Svetozar A. (2021). "Colliding stellar wind modelling of the X-ray emission from WR 140". Monthly Notices of the Royal Astronomical Society 500 (4): 4837. doi:10.1093/mnras/staa3591. Bibcode: 2021MNRAS.500.4837Z. 
  17. ↑ 17.0 17.1 Lau, Ryan M.; Hankins, Matthew J.; Han, Yinuo; Argyriou, Ioannis; Corcoran, Michael F.; Eldridge, Jan J.; Endo, Izumi; Fox, Ori D. et al. (2022-11-01). "Nested dust shells around the Wolf-Rayet binary WR 140 observed with JWST". Nature Astronomy 6 (11): 1308–1316. doi:10.1038/s41550-022-01812-x. ISSN 2397-3366. Bibcode: 2022NatAs...6.1308L. 
  18. ↑ 18.0 18.1 Lau, Ryan M.; Wang, Jason; Hankins, Matthew J.; Currie, Thayne; Deo, Vincent; Endo, Izumi; Guyon, Olivier; Han, Yinuo et al. (2023-07-01). "From Dust to Nanodust: Resolving Circumstellar Dust from the Colliding-wind Binary Wolf-Rayet 140". The Astrophysical Journal 951 (2): 89. doi:10.3847/1538-4357/acd4c5. ISSN 0004-637X. Bibcode: 2023ApJ...951...89L. 
  19. ↑ Monnier, J. D.; Tuthill, P. G.; Danchi, W. C. (2002-03-01). "Proper Motions of New Dust in the Colliding Wind Binary WR 140". The Astrophysical Journal 567 (2): L137–L140. doi:10.1086/340005. ISSN 0004-637X. Bibcode: 2002ApJ...567L.137M. 
  20. ↑ Han, Yinuo; Tuthill, Peter G.; Lau, Ryan M.; Soulain, Anthony (2022-10-01). "Radiation-driven acceleration in the expanding WR140 dust shell". Nature 610 (7931): 269–272. doi:10.1038/s41586-022-05155-5. ISSN 0028-0836. PMID 36224416. Bibcode: 2022Natur.610..269H. 
  21. ↑ "Episodic (and variable) dust-making WR stars". https://www.roe.ac.uk/~pmw/Wr140edm.htm. 
  22. ↑ Taranova, O. G.; Shenavrin, V. I. (2011-01-01). "WR 140 (=V1687 Cyg): Infrared photometry, 2001–2010". Astronomy Letters 37 (1): 30–39. doi:10.1134/S1063773710091014. ISSN 0320-0108. Bibcode: 2011AstL...37...30T. 
  23. ↑ McCaughrean, Mark. "Surprised no-one spotted my awful maths yet" (in en). https://x.com/markmccaughrean/status/1564229429949353988. 



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