HD 151932

HD 151932, also known as WR 78, is a Wolf-Rayet star located in the constellation Scorpius, close to the galactic plane. Its distance is around 1,300 parsecs (4,200 lightyears) away from the Earth.[9] Despite being a blue-colored Wolf-Rayet star, it is extremely reddened by interstellar extinction, so its apparent magnitude is brighter for longer-wavelength passbands.[4] HD 151932 lies about 22′ west of the open cluster NGC 6231, the center of the OB association Scorpius OB1; it is not clear whether it is a part of the association or not.[7] With an apparent magnitude of about 6.5,[4] it is one of the few Wolf-Rayet stars that can be seen with the naked eye (although it can only be seen with the naked eye under excellent viewing conditions).

HD 151932
Location of WR 78 (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension  16h 52m 19.24769s[1]
Declination −41° 51′ 16.2631″[1]
Apparent magnitude (V) 6.45 - 6.61[2]
Characteristics
Spectral type WN7h[3]
U−B color index -0.63[4]
B−V color index +0.27[4]
Variable type WR[2]
Astrometry
Radial velocity (Rv)−25.00[5] km/s
Proper motion (μ) RA: −1.914±0.169[6] mas/yr
Dec.: −2.402±0.097[6] mas/yr
Parallax (π)0.7679 ± 0.0649[6] mas
Distance4,200 ± 400 ly
(1,300 ± 100 pc)
Absolute magnitude (MV)–5.83[3]
Details
Mass22[3] M☉
Radius10.14[3] R☉
Luminosity (bolometric)630,000[3] L☉
Surface gravity (log g)3.5[7] cgs
Temperature50,100[3] K
Other designations
HD 151932, WR 78, V919 Sco, HR 6249, HIP 82543, SAO 227328, CD–41° 10972, Trumpler 24 322[8]
Database references
SIMBADdata
WR 78 lies directly west of NGC 6231, with the reddish ζ2 Scorpii to the south

Like most extremely massive stars, HD 151932 is losing mass via its stellar wind. The total rate of mass loss is 5×10−5 M☉/yr.[9] The multiplicity (i.e., whether the star is a single star or a binary star system) of HD 151932 has not been studied very much.[10] A periodic shift in the spectrum with a period of 3.3 days (implying it is a spectroscopic binary) has been noticed, but it may be spurious; the star appears to be a single star but may be orbiting face-on and/or with a lower-mass companion.[7]

The spectrum of HD 151932 is unusual: part of the He I absorption lines are known to be shifted towards the violet side of the electromagnetic spectrum – this has been interpreted as an expanding stellar shell.[7] Related to this is the fact that the Si IV line varies irregularly in radial velocity, the nature of which is largely unknown.[11] X-rays have been detected from this star, along with several other Wolf-Rayet stars such as WR 24 and WR 136.[9]

References
  1. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 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.
  3. 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". arXiv:1904.04687 [astro-ph.SR].
  4. Heske, A.; Wendker, H. J. (1985). "Further photometry and spectroscopy in the young cluster region TR 24/Sco OB 1". Astronomy and Astrophysics. 151: 309–314. Bibcode:1985A&A...151..309H.
  5. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. Retrieved 12 December 2016.
  6. 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.
  7. Seggewiss, W.; Moffat, A. F. (1979). "The intrinsically bright Wolf-Rayet stars of type WN 7. III - The probable single SCO OB 1 star HD 151932 with variable He I envelope". Astronomy and Astrophysics. 72 (3): 332–338. Bibcode:1979A&A....72..332S.
  8. "HD 151932". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 18 February 2017.
  9. Skinner, S. L.; Zhekov, S. A.; Güdel, M.; Schmutz, W.; Sokal, Kimberly R. "X-ray Emission from Nitrogen-Type Wolf-Rayet Stars". The Astronomical Journal. 139 (3): 825–838. arXiv:0912.1326. Bibcode:2010AJ....139..825S. doi:10.1088/0004-6256/139/3/825.
  10. De Becker, M.; Raucq, F. (2013). "Catalogue of particle-accelerating colliding-wind binaries". Astronomy & Astrophysics. 558. arXiv:1308.3149. Bibcode:2013A&A...558A..28D. doi:10.1051/0004-6361/201322074.
  11. Vreux, J. M.; Manfroid, J.; Scuflaire, R.; Magain, P. (1987). "HD 151932 variability revisited". Astronomy and Astrophysics. 180: L17–L19. Bibcode:1987A&A...180L..17V.
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