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WR 31a

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WR 31a

WR 31a is surrounded by a blue bubble nebula created by a powerful stellar wind impacting material expelled during earlier stages of the star's life.
Credit: ESA/Hubble & NASA; Acknowledgement: Judy Schmidt
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Carina
Right ascension 10h 53m 59.5776s[1]
Declination −60° 26′ 44.358″[1]
Apparent magnitude (V) 10.85[2]
Characteristics
Evolutionary stage Wolf–Rayet
Spectral type WN11h[3]
Apparent magnitude (B) 11.64±0.10
Apparent magnitude (V) 10.85±0.08
Apparent magnitude (R) 10.56±0.02
Apparent magnitude (G) 10.033±0.004
Apparent magnitude (J) 7.323±0.024
Apparent magnitude (H) 6.72±0.05
Apparent magnitude (K) 6.097±0.021
Apparent magnitude (g) 11.53±0.32
B−V color index 0.79
V−R color index 0.29
R−I color index 0.5
J−H color index 0.603
J−K color index 1.226
Variable type cLBV[4][5]
Astrometry
Proper motion (μ) RA: −3.6[2] mas/yr
Dec.: 4.0[2] mas/yr
Parallax (π)0.0418 ± 0.0299 mas[1]
Distance31,200+8,500
−6,000 ly
(9,570+2,600
−1,850 pc)
Absolute magnitude (MV)−6.71[6]
Details
Mass17+7
−4[7] M☉
Radius29.8+11.9
−6.1[7] R☉
Luminosity1,820,000[8] L☉
Temperature30,200 (1985-1992)[8] 27,500 (1991)[7] K
Other designations
WR 31a, Hen 3-519, He 3-519,[7] 2MASS J10535958-6026444, Gaia DR1 5338229111491506304, Gaia DR2 5338229115839425664, GSC 08958-01166, GSC2 S1113013697, UCAC2 5308747, UCAC4 148-066854, IRAS 10520-6010, TYC 8928-1166-1, AAVSO 1050–59, MSX5C G288.9347-00.8046
Database references
SIMBADdata

WR 31a, commonly referred to as Hen 3-519, is a Wolf–Rayet (WR) star in the southern constellation of Carina that is surrounded by an expanding Wolf–Rayet nebula. It is not a classical old stripped-envelope WR star, but a young massive star which still has some hydrogen left in its atmosphere.

History of observations

WR 31a was first published in 1952 as one of six peculiar emission line stars, but not given a designation at that time. It was described as having numerous P Cygni type lines with unusually broad emission components.[9] A year later it was listed as being associated with nebulosity, at the time thought to be a planetary nebula.[10]

In 1976, it was included in a catalogue of southern emission-line stars, the third catalogue of emission objects compiled by Karl Gordon Henize. The designation Hen 3-519, sometimes He 3-519, was adopted as the most common identifier for this star.[11] In 2001, it was listed in The Seventh Catalogue of Galactic Wolf-Rayet stars as entry 31a,[6] but it is still frequently called Hen 3-519.[5][4]

In 1994, WR 31a was first described as a candidate luminous blue variable (cLBV) after a detailed spectrographic study with the Anglo-Australian Telescope.[7]

Measurements of its parallax, published in 2017 as a result of the Gaia mission, suggested a much closer (6,500 light-year; 2,000 parsec) distance to WR 31a as well as to its neighbor, the luminous blue variable AG Carinae. It was thought that, if this distance was confirmed by Gaia's second data release (DR2) in 2018, this would mean both stars wer much less luminous than previously thought, and both may instead be former red supergiant stars.[12] However, Gaia's DR2 returned a parallax of 0.0418±0.0299 mas; using Bayesian inference, Smith et al. (2018) calculated its distance to be 31,200+8,500
−6,000 ly (9,570+2,600
−1,850 pc).[13]

Blue bubble

WR 31a is surrounded by a shell of ionised gas nearly eight light-years (2.5 pc) wide. The Hubble Space Telescope (HST) has captured a striking image of the nebula, rendering it as a thin blue bubble. In this false colour image, the blue colours represents red visible light (605 nm), while orange-red colours represent near infrared radiation at 814 nm.[14] Some media sources have wrongly claimed this deep-sky object was recently discovered by the HST,[15] but this nebula was originally found by Ellen Dorrit Hoffleit in 1953 and designated as the planetary nebula Hf 39.[10] Other planetary nebula catalogue names include ESO 128-18 and Wray 15-682.[10]

Since 2013, the nebula has been considered not as a planetary nebula, but rather as a much larger expanding gas shell, formally classified as a Wolf–Rayet nebula or WR nebula.[16] Its observed expansion velocity is 365 km/s (227 mi/s), and is estimated to be some 2.4 parsecs (7.8 ly) across.[17] The dynamical age of the nebula is estimated at 18,000 years and the total mass of ionised gas at 2–3 M☉.[7]

Properties

WR 31a itself, the highly luminous central star of the nebula, is invisible to the naked-eye at magnitude 10.85V. It has a spectral classification of WN11h, indicating a WR star with strong Nii emission but no Niii emission, and with hydrogen features visible in the spectrum.[17] The spectral classification WN11 was created for this star and AG Carinae since they did not fit into any existing spectral type and appeared to constitute an extension of the WR nitrogen sequence to cooler temperatures.[7] The progenitor's mass of the central star is estimated to have been about 45 times that of the Sun,[5] and this massive star will likely explode as a supernova in the future.[18]

The spectrum of WR 31a shows P Cygni profiles, most strongly on the dominant Hi, Hei, and Nii lines. These profiles may show dramatic changes on a timescale of weeks, with the absorption components of the lines sometimes disappearing completely.[7]

Variability

No significant brightness changes have been detected in WR 31a, but it has been listed as a candidate luminous blue variable because of its luminosity, temperature, and mass loss properties.[7] Van Genderen catalogued it as a dormant or ex-LBV because of the lack of characteristic LBV variations.[8] Possible small brightness changes have been seen in All Sky Automated Survey (ASAS) data,[19] WR 31a is included as a variable star in the International Variable Star Index,[20] although not in the General Catalogue of Variable Stars.[21]

References

  1. ^ a b c 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.
  2. ^ a b c Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). The Tycho-2 catalogue of the 2.5 million brightest stars. Vol. 355. pp. L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862. ISBN 978-0333750889. {{cite book}}: |journal= ignored (help)
  3. ^ Toalá, J. A.; Guerrero, M. A.; Ramos-Larios, G.; Guzmán, V. (2015). "WISE morphological study of Wolf-Rayet nebulae". Astronomy & Astrophysics. 578: A66. arXiv:1503.06878. Bibcode:2015A&A...578A..66T. doi:10.1051/0004-6361/201525706.
  4. ^ a b Nazé, Y.; Rauw, G.; Hutsemékers, D. (2012). "The first X-ray survey of Galactic luminous blue variables". Astronomy & Astrophysics. 538: A47. arXiv:1111.6375. Bibcode:2012A&A...538A..47N. doi:10.1051/0004-6361/201118040.
  5. ^ a b c Smith, Nathan; Tombleson, Ryan (2015). "Luminous blue variables are antisocial: Their isolation implies that they are kicked mass gainers in binary evolution". Monthly Notices of the Royal Astronomical Society. 447 (1): 598–617. arXiv:1406.7431. Bibcode:2015MNRAS.447..598S. doi:10.1093/mnras/stu2430.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  6. ^ a b Van Der Hucht, Karel A. (2001). "The VIIth catalogue of galactic Wolf-Rayet stars". New Astronomy Reviews. 45 (3): 135–232. Bibcode:2001NewAR..45..135V. doi:10.1016/S1387-6473(00)00112-3.
  7. ^ a b c d e f g h i Smith, L. J.; Crowther, P. A.; Prinja, R. K. (1994). "A study of the luminous blue variable candidate He 3-519 and its surrounding nebula". Astronomy and Astrophysics. 281 (3): 833–854. Bibcode:1994A&A...281..833S.
  8. ^ a b c Van Genderen, A. M. (2001). "S Doradus variables in the Galaxy and the Magellanic Clouds". Astronomy and Astrophysics. 366 (2): 508–531. Bibcode:2001A&A...366..508V. doi:10.1051/0004-6361:20000022.Vizie database entry
  9. ^ Henize, Karl G. (1952). "Six Peculiar Hα-Emission Stars". Astrophysical Journal. 115: 133. Bibcode:1952ApJ...115..133H. doi:10.1086/145522.
  10. ^ a b c Hoffleit, Dorrit (1953). "A preliminary survey of nebulosities and associated B-stars in Carina". Annals of Harvard College Observatory. 119: 37. Bibcode:1953AnHar.119...37H.
  11. ^ Henize, K. G. (1976). "Observations of southern emission-line stars". Astrophysical Journal Supplement Series. 30: 491. Bibcode:1976ApJS...30..491H. doi:10.1086/190369.
  12. ^ Smith, Nathan; Stassun, Keivan G. (March 2017). "The Canonical Luminous Blue Variable AG Car and Its Neighbor Hen 3-519 are Much Closer than Previously Assumed". The Astronomical Journal. 153 (3). 125. arXiv:1610.06522. Bibcode:2017AJ....153..125S. doi:10.3847/1538-3881/aa5d0c.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  13. ^ Smith, Nathan; et al. (8 May 2018). "On the Gaia DR2 distances for Galactic Luminous Blue Variables". arXiv:1805.03298 [astro-ph.SR].
  14. ^ "Hubble's Blue Bubble". NASA. 26 February 2016. Retrieved 1 March 2016.
  15. ^ "Hubble Captures "Blue Bubble' Star—20 Times Bigger, a Million Times Brighter than the Sun's". Inquisitr. Retrieved 2 March 2016.
  16. ^ Frew, D. J.; Bojicic, I. S.; Parker, Q. A. (2013). "A catalogue of integrated Hα fluxes for 1258 Galactic planetary nebulae". Monthly Notices of the Royal Astronomical Society. 431 (1): 2–26. arXiv:1211.2505. Bibcode:2013MNRAS.431....2F. doi:10.1093/mnras/sts393.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  17. ^ a b Toalá, J. A.; Guerrero, M. A.; Ramos-Larios, G.; Guzmán, V. (2015). "WISE morphological study of Wolf-Rayet nebulae". Astronomy & Astrophysics. 578: A66. arXiv:1503.06878. Bibcode:2015A&A...578A..66T. doi:10.1051/0004-6361/201525706.
  18. ^ "Blue bubble in Carina". NASA. Retrieved 2 March 2016.
  19. ^ Pojmanski, G. (2002). "The All Sky Automated Survey. Catalog of Variable Stars. I. 0 h – 6 h Quarter of the Southern Hemisphere". Acta Astronomica. 52: 397–427. arXiv:astro-ph/0210283. Bibcode:2002AcA....52..397P.
  20. ^ "Hen 3-519". International Variable Star Index. American Association of Variable Star Observers. 4 January 2010. Retrieved 30 September 2016.
  21. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
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