WR 25

WR 25 (HD 93162) is a binary star system in the turbulent star-forming region the Carina Nebula, about 6,800 light-years from Earth. It contains a Wolf-Rayet star and a hot luminous companion and is a member of the Trumpler 16 cluster. The name comes from the Catalogue of Galactic Wolf–Rayet Stars.

WR 25
Location of WR 25 (circled)
Credit: ESO
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Carina
Right ascension 10h 44m 10.337s[1]
Declination −59° 43′ 11.41″[1]
Apparent magnitude (V) 8.80[2]
Characteristics
Evolutionary stage Wolf-Rayet star
Spectral type O2.5If*/WN6 + OB[3]
Astrometry
Radial velocity (Rv)−34.6[4] km/s
Proper motion (μ) RA: -6.918[5] mas/yr
Dec.: 2.764[5] mas/yr
Parallax (π)0.4450 ± 0.0203 mas[5]
Distance1,970+180
−150[6] pc
Absolute magnitude (MV)–6.98[7]
Orbit[4]
Period (P)207.85 days
Semi-major axis (a)156 R☉
Eccentricity (e)0.50
Semi-amplitude (K1)
(primary)		44 km/s
Details
WR
Mass98[7] M☉
Radius20.24[7] R☉
Luminosity (bolometric)2,400,000[7] L☉
Temperature50,100[7] K
Other designations
HD 93162, 2MASS J10441038-5943111, WR 25, XMMU J104410.3-594311, CD−59°3282, PPM 339385, SAO 238408, Trumpler 16 177, GSC 08626-01989, UBV 9882, Hen 3-478
Database references
SIMBADdata

Spectrum

WR 25 was recognised as a Wolf–Rayet star in the 19th century, because of its brightness and a spectrum dominated by broad emission lines.[8] The spectrum contains lines of hydrogen and is intermediate between a classical WN (Wolf-Rayet) star and an O-type supergiant. This led to early reports that it was a binary, for example a WN7 star plus an O7 star.[9] It has also been described as WN7 + abs[10] (meaning a Wolf-Rayet star with absorption lines of unknown origin) and WN6ha.[11] With the introduction of specific classifications for hot slash stars, WR 25 was assigned the spectral type O2.5If*/WN6. This recognises the presence of nitrogen, the intrinsic weakness of many emission lines, and the presence of some helium and hydrogen absorption lines. The classification represents a fine gradation of weaker emission and stronger absorption than a WN6ha spectral type.[12] Any contribution to the spectrum from the companion cannot be clearly detected.[4]

Properties
WR 25 is the brightest star in the image. The orange star to its left is a foreground object.

The primary star of the WR 25 system is approximately 2.4 million times brighter than the Sun and illuminates the far southern end of the Trumpler 16 cluster. The model used to derive the stellar parameters is unsuitable for use in binary systems with the authors noting that the companion contributes more than 15% of the system luminosity, so the luminosity is highly uncertain. Earlier estimates based on measurements of the ionising flux produced values around 1.5 million times the sun, with correspondingly lower estimates for other physical data.[13]

The companion is assumed to be a young hot massive star, similar to other known WR+O or WR+WR binaries. It has been reported as an O4 supergiant, but later measurements are still uncertain about the exact spectral type. Colliding stellar winds between two such hot luminous stars produce the hard X-rays[14] that led to suspicion about the binary status long before the 208-day orbital period was detected.[4]

Although very luminous, WR 25 is beyond naked-eye visibility due to heavy dust extinction of clouds in the nebula, and because much of the emitted radiation is in the ultraviolet. With an absolute magnitude of −6.98 at a distance of 1970 parsecs, it would be visible to the naked eye with a stellar magnitude of 4.49 if there were nothing in the way, rather than the actual 8.80. It has been observed in X-rays and infra-red.[14][15]

WR 25 lies at the western limit of the Trumpler 16 star cluster, part of Carina OB1, one of the largest stellar associations in the Milky Way Galaxy.[16] Because of its extreme luminosity it greatly affects its stellar environment, seen in the thin long arcs and filaments moving away from the star, including the Finger Nebula.[17]

See also

References
  1. Roeser, S.; Bastian, U. (1988). "A new star catalogue of SAO type". Astronomy and Astrophysics Supplement Series. 74: 449. Bibcode:1988A&AS...74..449R. ISSN 0365-0138.
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  3. Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J. (2014). "The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars". The Astrophysical Journal Supplement. 211 (1): 10. arXiv:1312.6222. Bibcode:2014ApJS..211...10S. doi:10.1088/0067-0049/211/1/10. S2CID 118847528.
  4. Gamen, R.; Gosset, E.; Morrell, N.; Niemela, V.; Sana, H.; Nazé, Y.; Rauw, G.; Barbá, R.; Solivella, G. (2006). "The first orbital solution for the massive colliding-wind binary HD 93162 (≡WR 25)". Astronomy and Astrophysics. 460 (3): 777–782. arXiv:astro-ph/0609454. Bibcode:2006A&A...460..777G. doi:10.1051/0004-6361:20065618. S2CID 17677713.
  5. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  6. Crowther, Paul A.; Rate, Gemma (2020). "Unlocking Galactic Wolf–Rayet stars with Gaia DR2 – I. Distances and absolute magnitudes". Monthly Notices of the Royal Astronomical Society. 493 (1): 1512–1529. arXiv:1912.10125. Bibcode:2020MNRAS.493.1512R. doi:10.1093/mnras/stz3614. S2CID 209444955.
  7. Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J.; Oskinova, L. M. (2019). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". Astronomy & Astrophysics. A57: 625. arXiv:1904.04687. Bibcode:2019A&A...625A..57H. doi:10.1051/0004-6361/201834850. S2CID 104292503.
  8. Campbell, W. W. (1894). "The Wolf-Rayet stars". Astronomy and Astro-Physics. 13: 448. Bibcode:1894AstAp..13..448C.
  9. Smith, Lindsey F. (1968). "A revised spectral classification system and a new catalogue for galactic Wolf-Rayet stars". Monthly Notices of the Royal Astronomical Society. 138: 109–121. Bibcode:1968MNRAS.138..109S. doi:10.1093/mnras/138.1.109.
  10. Crowther, Paul A.; Smith, Linda J.; Hillier, D. John (1993). "Tailored analyses of 24 Galactic WN stars". Space Science Reviews. 66 (1–4): 271–275. Bibcode:1993SSRv...66..271C. doi:10.1007/BF00771076. S2CID 122574673.
  11. Smith, Lindsey F.; Maeder, A. (1998). "The relationship between the WR classification and stellar models. II. The WN stars without hydrogen". Astronomy and Astrophysics. 334: 845. Bibcode:1998A&A...334..845S.
  12. Crowther, Paul A.; Walborn, Nolan R. (2011). "Spectral classification of O2-3.5 If*/WN5-7 stars". Monthly Notices of the Royal Astronomical Society. 416 (2): 1311. arXiv:1105.4757. Bibcode:2011MNRAS.416.1311C. doi:10.1111/j.1365-2966.2011.19129.x. S2CID 118455138.
  13. Crowther, P. A.; Dessart, L. (1998). "Quantitative spectroscopy of Wolf--Rayet stars in HD 97950 and R136a -- the cores of giant H II regions". Monthly Notices of the Royal Astronomical Society. 296 (3): 622–642. Bibcode:1998MNRAS.296..622C. doi:10.1046/j.1365-8711.1998.01400.x.
  14. Pandey, J. C.; Pandey, S. B.; Karmakar, S. (2014). "Phase-Resolvedxmm-Newtonandswiftobservations of Wr 25". The Astrophysical Journal. 788 (1): 84. arXiv:1405.7137. Bibcode:2014ApJ...788...84P. doi:10.1088/0004-637X/788/1/84. S2CID 119197173.
  15. Sanchawala, K.; Chen, W. P.; Lee, H. T.; Chu, Y. H.; Nakajima, Y.; Tamura, M.; Baba, D.; Sato, S. (2007). "An X‐Ray and Near‐Infrared Study of Young Stars in the Carina Nebula". The Astrophysical Journal. 656 (1): 462–473. Bibcode:2007ApJ...656..462S. CiteSeerX 10.1.1.667.3955. doi:10.1086/510184. S2CID 53352850.
  16. Wolk, Scott J.; Broos, Patrick S.; Getman, Konstantin V.; Feigelson, Eric D.; Preibisch, Thomas; Townsley, Leisa K.; Wang, Junfeng; Stassun, Keivan G.; King, Robert R.; McCaughrean, Mark J.; Moffat, Anthony F. J.; Zinnecker, Hans (2011). "The Chandra Carina Complex Project View of Trumpler 16". The Astrophysical Journal Supplement. 194 (1): 12. arXiv:1103.1126. Bibcode:2011ApJS..194...12W. doi:10.1088/0067-0049/194/1/12. S2CID 13951142.
  17. Walborn, Nolan R. (2012). "The Company Eta Carinae Keeps: Stellar and Interstellar Content of the Carina Nebula". Eta Carinae and the Supernova Impostors. Astrophysics and Space Science Library. 384: 25–42. Bibcode:2012ASSL..384...25W. doi:10.1007/978-1-4614-2275-4_2. ISBN 978-1-4614-2274-7.
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