WR 102

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WR 102
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension  17h 45m 47.5s[1]
Declination −26° 10′ 27″[1]
Apparent magnitude (V) 14.10[2]
Evolutionary stage Wolf-Rayet star
Spectral type WO2[3]
B−V color index +0.77[4]
Parallax (π)0.3467 ± 0.0283[5] mas
Distance9,400 ± 800 ly
(2,900 ± 200 pc)
Absolute magnitude (MV)−1.71[2]
[6] M
[6] R
[6] L
Temperature210,000[3] K
Metallicity [Fe/H]0.0[3] dex
Other designations
V3893 Sagittarii, LS 4368, ALS 4368, Sand 4
Database references

WR 102 is a Wolf-Rayet star in the constellation Sagittarius, an extremely rare star on the WO oxygen sequence. It is a luminous and very hot star, highly evolved and close to exploding as a supernova.


WR 102 was first mentioned as the possible optical counterpart to a peculiar X-ray source GX 3+1.[7] However, it became clear that it was a separate object and in 1971 it was highlighted as a luminous star with unusual OVI emission lines in its spectrum.[8] It was classified as a WC star, an unusual one because of the highly-ionised emission lines, and not the central star of a planetary nebula.[7][9] It was seen to vary in brightness and was given the variable star designation V3893 Sagittarii in the 62nd name-list of variable stars.[10]

Faint nebulosity was discovered around WR 102 in 1981 and was identified as a wind-blown bubble.[11] In 1982, a set of five luminous stars with highly-ionised oxygen emission lines, including WR 102, was used to define the WO class of Wolf-Rayet stars. They were identified as highly-evolved massive stars.[12]


Infrared image of the nebulosity around WR 102 (WISE)

WR 102, of spectral classification WO2, is one of the very few known oxygen-sequence Wolf-Rayet stars, just four in the Milky Way galaxy and five in external galaxies. It is also the hottest known with a surface temperature of 210,000 K. Modelling the atmosphere gives a luminosity around 282,000 L,[3] while calculations from brightness and distance gives luminosity of nearly 100,000 L with a distance of 2,600±200[6] parsec. It is a very small dense star, with a radius around 0.23 R and a mass of 7.0 M[6].

Very strong stellar winds with a terminal velocity of 5,000 kilometers per second are causing WR 102 to lose 10−5 M/year.[2] For comparison, the Sun loses (2-3) x 10−14 solar masses per year due to its solar wind, several hundred million times less than WR 102. These winds and the strong ultraviolet radiation from the hot star have compressed and ionised the surrounding interstellar material into a complex series of arcs described as the bubble type of Wolf-Rayet nebula.[13]

Evolutionary status[edit]

WO stars are the last evolutionary stage of the most massive stars before exploding as supernovae.[14] It is very likely that WR 102 is on its last stages of nuclear fusion, near or beyond the end of helium burning.[15]

It has been calculated that WR 102 will explode as a supernova within 1,500 years.[3] High mass and rapid rotation would make a gamma-ray burst (GRB) possible,[14] but it is unclear if WR 102 is rotating rapidly.[3]. It was previously thought that the projected rotation velocity within the stellar wind could be as fast as 1,000 km/s [2] but spectropolarimetric observations seem to indicate that if WR 102 is rotating, it is rotating at a much lower speed[6].

See also[edit]


  1. ^ a b Dufton, P. L.; Smartt, S. J.; Hambly, N. C. (2001). "A UKST survey of blue objects towards the Galactic centre - seven additional fields" (PDF). Astronomy and Astrophysics. 373 (2): 608–624. Bibcode:2001A&A...373..608D. doi:10.1051/0004-6361:20010613. ISSN 0004-6361.
  2. ^ a b c d Sander, A.; Hamann, W. -R.; Todt, H. (2012). "The Galactic WC stars" (PDF). Astronomy & Astrophysics. 540: A144. arXiv:1201.6354. Bibcode:2012A&A...540A.144S. doi:10.1051/0004-6361/201117830.
  3. ^ a b c d e f Tramper, F.; Straal, S. M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J. S.; de Mink, S. E.; Kaper, L. (2015). "Massive stars on the verge of exploding: The properties of oxygen sequence Wolf-Rayet stars" (PDF). Astronomy & Astrophysics. 581 (110): A110. arXiv:1507.00839v1. Bibcode:2015A&A...581A.110T. doi:10.1051/0004-6361/201425390.
  4. ^ Smith, Lindsey F.; Shara, Michael M.; Moffat, Anthony F. J. (1990). "Distances of Galactic WC stars from emission-line fluxes and a quantification of the WC classification". The Astrophysical Journal. 358: 229. Bibcode:1990ApJ...358..229S. doi:10.1086/168978. ISSN 0004-637X.
  5. ^ Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  6. ^ a b c d e f Stevance, H F; Ignace, R; Crowther, P A; Maund, J R; Davies, B; Rate, G (2018). "Probing the rotational velocity of Galactic WO stars with spectropolarimetry". Monthly Notices of the Royal Astronomical Society. 479 (4): 4535–4543. arXiv:1807.02117. Bibcode:2018MNRAS.479.4535S. doi:10.1093/mnras/sty1827.
  7. ^ a b Sanduleak, N. (1971). "On Stars Having Strong O VI Emission". The Astrophysical Journal. 164: L71. Bibcode:1971ApJ...164L..71S.
  8. ^ Stephenson, C. B.; Sanduleak, N. (1971). "Luminous stars in the Southern Milky Way". Publications of the Warner & Swasey Observatory. 1: 1. Bibcode:1971PW&SO...1a...1S.
  9. ^ Stenholm, B. (1975). "Wolf-Rayet stars and galactic structure". Astronomy and Astrophysics. 39: 307. Bibcode:1975A&A....39..307S.
  10. ^ Kukarkin, B. V.; Kholopov, P. N.; Fedorovich, V. P.; Kireyeva, N. N.; Kukarkina, N. P.; Medvedeva, G. I.; Perova, N. B. (1977). "62nd Name-List of Variable Stars". Information Bulletin on Variable Stars. 1248: 1. Bibcode:1977IBVS.1248....1K.
  11. ^ Chu, Y. -H (1981). "Galactic ring nebulae associated with Wolf-rayet stars. I. Introduction and classification". The Astrophysical Journal. 249: 195. Bibcode:1981ApJ...249..195C.
  12. ^ Barlow, M. J.; Hummer, D. G. (1982). "The WO Wolf-rayet stars". Wolf-Rayet Stars: Observations. 99: 387. Bibcode:1982IAUS...99..387B.
  13. ^ Toalá, J. A.; Guerrero, M. A.; Ramos-Larios, G.; Guzmán, V. (2015). "WISE morphological study of Wolf-Rayet nebulae" (PDF). Astronomy & Astrophysics. 578: A66. arXiv:1503.06878. Bibcode:2015A&A...578A..66T. doi:10.1051/0004-6361/201525706.
  14. ^ a b Groh, Jose H.; Meynet, Georges; Georgy, Cyril; Ekstrom, Sylvia (2013). "Fundamental properties of core-collapse Supernova and GRB progenitors: Predicting the look of massive stars before death" (PDF). Astronomy & Astrophysics. 558: A131. arXiv:1308.4681v1. Bibcode:2013A&A...558A.131G. doi:10.1051/0004-6361/201321906.
  15. ^ Groh, Jose H.; Meynet, Georges; Ekström, Sylvia; Georgy, Cyril (2014). "The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage" (PDF). Astronomy & Astrophysics. 564: A30. arXiv:1401.7322. Bibcode:2014A&A...564A..30G. doi:10.1051/0004-6361/201322573.