Gamma Velorum

Gamma Velorum (Latinised from γ Velorum, abbreviated γ Vel) is a quadruple star system in the constellation Vela. At a combined magnitude +1.7, it is one of the brightest stars in the night sky, and contains by far the closest and brightest Wolf-Rayet star. It has the traditional name Suhail al Muhlif and the modern name Regor /ˈriːɡɔːr/,[15] but neither is approved by the International Astronomical Union.

γ2 Velorum
Observation data
Epoch J2000      Equinox J2000
Constellation Vela
Right ascension 08h 09m 31.95013s[1]
Declination –47° 20′ 11.7108″[1]
Apparent magnitude (V) 1.83[2] (1.81 - 1.87[3])
Characteristics
Spectral type WC8 + O7.5III[4]
U−B color index −0.94[2]
B−V color index −0.25[2]
Variable type Wolf-Rayet[3]
Astrometry
Radial velocity (Rv)+12 ± 1[5] km/s
Proper motion (μ) RA: –6.07[1] mas/yr
Dec.: +10.43[1] mas/yr
Parallax (π)2.92 ± 0.30[1] mas
Distance379+4
−4[6] pc
Absolute magnitude (MV)−4.23 + −5.63[7]
Details
WR
Mass9.0 ± 0.6[7] M☉
Radius6 ± 3[7] R☉
Luminosity (bolometric)170,000[7] L☉
Temperature57,000[8] K
Age3.5[9] -5.5[10] Myr
O
Mass28.5 ±1.1[7] M☉
Radius17 ± 2[7] R☉
Luminosity (bolometric)280,000[7] L☉
Temperature35,000[8] K
Age3.5[9]-5.5[10] Myr
Orbit[11]
PrimaryO
CompanionWR
Period (P)78.53 ± 0.01 days
Semi-major axis (a)1.2[7] AU
Eccentricity (e)0.326 ± 0.01
Inclination (i)65 ± 8°
Periastron epoch (T)2,450,120.5 ± 2
Argument of periastron (ω)
(secondary)		248 ± 4°
Semi-amplitude (K1)
(primary)		38.4 ± 2 km/s
Semi-amplitude (K2)
(secondary)		122 ± 2 km/s
Other designations
Regor, Suhail Al-Muhlif, CD−46°3847, FK5 309, HD 68273, HIP 39953, HR 3207, SAO 219504, WR 11
Database references
SIMBADdata
γ1 Velorum
Observation data
Epoch J2000      Equinox J2000
Constellation Vela
Right ascension 08h 09m 29.3260s[12]
Declination –47° 20′ 43.027″[12]
Apparent magnitude (V) 4.27[13]
Characteristics
Spectral type B2III[9]
U−B color index −0.92[13]
B−V color index −0.22[13]
Astrometry
Radial velocity (Rv)+9.7 ± 1[13] km/s
Proper motion (μ) RA: –0.6[14] mas/yr
Dec.: +9.7[14] mas/yr
Absolute magnitude (MV)−3.62[9]
Details
Mass14[9] M☉
Age8[9] Myr
Other designations
CD−46°3846, HD 68243, HR 3206, SAO 219501
Database references
SIMBADdata

The γ Velorum system includes a pair of stars separated by 41", each of which is also a spectroscopic binary system. γ2 Velorum, the brighter of the visible pair, contains the Wolf-Rayet star and a blue supergiant, while γ1 Velorum contains a blue giant and an unseen companion.

Distance
Location of γ Velorum (circled)

Gamma Velorum is close enough to have accurate parallax measurements as well as distance estimates by more indirect means. The Hipparcos parallax for γ2 implies a distance of 342 pc. A dynamical parallax derived from calculations of the orbital parameters gives a value of 336 pc, similar to spectrophotometric derivations. A VLTI interferometry measurement of the distance gives a slightly larger value of 368 ± 51 pc. All these distances are somewhat less than the commonly assumed distance of 450 pc for the Vela OB2 association which is the closest grouping of young massive stars.[16]

Stellar system

The Gamma Velorum system is composed of at least four stars. The brightest member, γ2 Velorum or γ Velorum A, is a spectroscopic binary composed of a blue supergiant of spectral class O7.5 (~30 M☉), and a massive Wolf-Rayet star (~9 M☉, originally ~35 M☉).[10] The binary has an orbital period of 78.5 days and separation varying from 0.8 to 1.6 astronomical units. The Wolf-Rayet star is likely to end its life in a Type Ib supernova explosion; it is one of the nearest supernova candidates to the Sun.[17] The Wolf-Rayet star has traditionally been regarded as the primary since its emission lines dominate the spectrum, but the O star is visually brighter and also more luminous. For clarity, the components are now often referred to as WR and O.[7]

The bright (apparent magnitude +4.2) γ1 Velorum or γ Velorum B, is a spectroscopic binary with a period of 1.48 days. Only the primary is detected and it is a blue-white giant. It is separated from the Wolf-Rayet binary by 41.2", easily resolved with binoculars.[9] The pair are too close to be separated without optical assistance, and they appear to the naked eye as a single star of apparent magnitude 1.72 (at the average brightness of γ2 of 1.83).

Gamma Velorum has several fainter companions that share a common motion and are likely to be members of the Vela OB2 association.[9] The magnitude +7.3 CD-46 3848 is a white F0 star at is 62.3 arcseconds from the A component. At 93.5 arcseconds is another binary star, an F0 star of magnitude +9.2.

γ Velorum is associated with several hundred pre main sequence stars within less than a degree. The ages of these stars would be at least 5 million years.[9]

Etymology

The Arabic name is al Suhail al Muḥlīf. al Muhlif refers to the oath-taker, and al Suhail is originally derived from a word meaning the plain. Suhail is used for at least three other stars: Canopus; λ Velorum (al Suhail al Wazn); and ζ Puppis (Suhail Hadar). Suhail is also a common Arabic male first name.[18]

In Chinese, 天社 (Tiān Shè), meaning Celestial Earth God's Temple, refers to an asterism consisting of γ2 Velorum, δ Velorum, κ Velorum and b Velorum.[19] Consequently, γ2 Velorum itself is known as 天社一 (Tiān Shè yī), "the First Star of Celestial Earth God's Temple".[20]

The name Regor ("Roger" spelled in reverse) was invented as a practical joke by the Apollo 1 astronaut Gus Grissom for his fellow astronaut Roger Chaffee.[21]

Due to the exotic nature of its spectrum (bright emission lines in lieu of dark absorption lines) it is also dubbed the Spectral Gem of Southern Skies.[22]

See also

References
  1. van Leeuwen, F. (November 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, S2CID 18759600
  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. 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: 02025. Bibcode:2009yCat....102025S.
  4. Roche, P. F.; Colling, M. D.; Barlow, M. J. (2012). "The outer wind of γ Velorum". Monthly Notices of the Royal Astronomical Society. 427 (1): 581. arXiv:1208.6016. Bibcode:2012MNRAS.427..581R. doi:10.1111/j.1365-2966.2012.22005.x. S2CID 119234167.
  5. Niemela, V. S.; Sahade, J. (1980). "The orbital elements of Gamma 2 Velorum". The Astrophysical Journal. 238: 244. Bibcode:1980ApJ...238..244N. doi:10.1086/157981. ISSN 0004-637X.
  6. Parker, Richard J.; Crowther, Paul A.; Rate, Gemma (2020). "Unlocking Galactic Wolf–Rayet stars with Gaia DR2 – II. Cluster and association membership". Monthly Notices of the Royal Astronomical Society. 495 (1): 1209–1226. arXiv:2005.02533. Bibcode:2020MNRAS.495.1209R. doi:10.1093/mnras/staa1290. S2CID 218516882.
  7. North, J. R.; Tuthill, P. G.; Tango, W. J.; Davis, J. (2007). "Γ2 Velorum: Orbital solution and fundamental parameter determination with SUSI". Monthly Notices of the Royal Astronomical Society. 377 (1): 415–424. arXiv:astro-ph/0702375. Bibcode:2007MNRAS.377..415N. doi:10.1111/j.1365-2966.2007.11608.x. S2CID 16425744.
  8. De Marco, O.; Schmutz, W.; Crowther, P. A.; Hillier, D. J.; Dessart, L.; De Koter, A.; Schweickhardt, J. (2000). "The gamma Velorum binary system. II. WR stellar parameters and the photon loss mechanism". Astronomy and Astrophysics. 358: 187. arXiv:astro-ph/0004081. Bibcode:2000A&A...358..187D.
  9. Jeffries, R. D.; Naylor, T.; Walter, F. M.; Pozzo, M. P.; Devey, C. R. (2009). "The stellar association around Gamma Velorum and its relationship with Vela OB2". Monthly Notices of the Royal Astronomical Society. 393 (2): 538. arXiv:0810.5320. Bibcode:2009MNRAS.393..538J. doi:10.1111/j.1365-2966.2008.14162.x. S2CID 17560818.
  10. Eldridge, J. J. (2009). "A new-age determination for γ2 Velorum from binary stellar evolution models". Monthly Notices of the Royal Astronomical Society: Letters. 400 (1): L20–L23. arXiv:0909.0504. Bibcode:2009MNRAS.400L..20E. doi:10.1111/j.1745-3933.2009.00753.x. S2CID 15765252.
  11. Schmutz, W.; Schweickhardt, J.; Stahl, O.; Wolf, B.; Dumm, T.; Gang, Th.; Jankovics, I.; Kaufer, A.; Lehmann, H.; Mandel, H.; Peitz, J.; Rivinius, Th. (1997). "The orbital motion of gamma^2 Velorum". Astronomy and Astrophysics. 328: 219. Bibcode:1997A&A...328..219S.
  12. Hog, E.; Kuzmin, A.; Bastian, U.; Fabricius, C.; Kuimov, K.; Lindegren, L.; Makarov, V. V.; Roeser, S. (1998). "The TYCHO Reference Catalogue". Astronomy and Astrophysics. 335: L65. Bibcode:1998A&A...335L..65H.
  13. Hernandez, C. A.; Sahade, J. (1980). "The Spectroscopic Binary GAMMA-1-VELORUM". Publications of the Astronomical Society of the Pacific. 92: 819. Bibcode:1980PASP...92..819H. doi:10.1086/130756. ISSN 0004-6280.
  14. 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". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862.
  15. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  16. Millour, F.; Petrov, R. G.; Chesneau, O.; Bonneau, D.; Dessart, L.; Bechet, C.; Tallon-Bosc, I.; Tallon, M.; Thiébaut, E.; Vakili, F.; Malbet, F.; Mourard, D.; Antonelli, P.; Beckmann, U.; Bresson, Y.; Chelli, A.; Dugué, M.; Duvert, G.; Gennari, S.; Glück, L.; Kern, P.; Lagarde, S.; Le Coarer, E.; Lisi, F.; Perraut, K.; Puget, P.; Rantakyrö, F.; Robbe-Dubois, S.; Roussel, A.; et al. (2007). "Direct constraint on the distance of γ2 Velorum from AMBER/VLTI observations". Astronomy and Astrophysics. 464 (1): 107–118. arXiv:astro-ph/0610936. Bibcode:2007A&A...464..107M. doi:10.1051/0004-6361:20065408. S2CID 15349002.
  17. Beech, Martin (2011). "The past, present and future supernova threat to Earth's biosphere". Astrophysics and Space Science. 336 (2): 287–302. Bibcode:2011Ap&SS.336..287B. doi:10.1007/s10509-011-0873-9. S2CID 119803426.
  18. Allen, R. H. (1963). Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc. ISBN 0-486-21079-0.
  19. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  20. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  21. Apollo 15 Lunar Surface Journal, Post-landing Activities, commentary at 105:11:33
  22. Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven, Conn.: Yale University Observatory, 5th Rev.ed. Bibcode:1991bsc..book.....H.
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