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VV Cephei

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VV Cephei
Cepheus constellation crop VV Cephei location.png

Location of VV Cephei in Cepheus constellation
Observation data
Epoch J2000      Equinox J2000
Constellation Cepheus
Right ascension 21h 56m 39.14385s[1]
Declination +63° 37′ 32.0174″[1]
Apparent magnitude (V) 4.91[2] (4.80 - 5.36[3])
Characteristics
U−B color index +0.43[4]
B−V color index +1.73[4]
Variable type EA + SRc[3]
A
Spectral type M2 Iab[2]
U−B color index +2.07[4]
B−V color index +1.82[4]
B
Spectral type B0-2 V[2]
U−B color index −0.52[4]
B−V color index +0.36[4]
Astrometry
Parallax (π)1.33 ± 0.20[1] mas
Distance4.9k ly
(1.5k[5] pc)
Absolute magnitude (MV)−6.93[6]
Orbit
Period (P)7,430.5 days[7]
Semi-major axis (a)16.2 ± 3.7[2]"
(24.8[8] AU)
Eccentricity (e)0.346 ± 0.01[7]
Inclination (i)84[9]°
Semi-amplitude (K1)
(primary)
19.43 ± 0.33[7] km/s
Semi-amplitude (K2)
(secondary)
19.14 ± 0.68[7] km/s
Details
A
Mass2.5[10] or 18.2[8] M
Radius1,400[11], 1,050[9]-1,900[12] R
Diameter1,400[11], 1,050[9]-1,900[12] D
Luminosity200,000[13] L
Surface gravity (log g)0.0[14] cgs
Temperature3,826[2] K
Metallicity [Fe/H]−0.06[14] dex
B
Mass8[10] or 18.6[8] M
Radius13[7]-25[15] R
Metallicity−0.14[16]
Age25[17] Myr
Other designations
VV Cep, HR 8383, HIP 108317, HD 208816, BD+62°2007, WDS J21567+6338, 2MASS J21563917+6337319, IRAS 21552+6323, AAVSO 2153+63
Database references
SIMBADdata

VV Cephei, also known as HD 208816, is an eclipsing binary star 4,900 light years away from Earth. VV Cephei A, the main companion, is a red supergiant that fills the system's Roche lobe when closest to a companion star, a blue main sequence star called VV Cephei B. Matter flows from the red supergiant into orbiting the blue companion for at least part of the orbit and the blue star is blocked from view by a large disk of material. VV Cephei A is currently recognised as one of the largest stars in the Milky Way with a diameter pulsating between 1,050 to 1,900 solar radii (4.9 to 8.8 au; 730,000,000 to 1.32×109 km). Thus, if VV Cephei A were placed in the center of the Solar System, it would engulf the orbit of Saturn, possibly even the orbit of Uranus.

Spectrum[edit]

The spectrum of VV Cep can be broken down into two main components, one for VV Cephei A and VV Cephei B. The material surrounding VV Cephei B generates emission lines, including [FeII] forbidden lines which is not common for other stars surrounded by circumstellar disks. The hydrogen emission lines are double-peaked due to a narrow central absorption component. This is caused by seeing the disk almost by its edge on where it intercepts continuum radiation from the star.[18]

Distance[edit]

The distance has been estimated by a variety of astronomical techniques to be around 1,5 kiloparsecs, while the Hipparcos parallax measurement produces a distance considerably below 1 kiloparsec.[1] From the distance, with the extinction measured at 1.24 magnitudes,[9] the absolute magnitude of the VV Cephei system as a whole is fairly well defined.

Properties[edit]

Relative sizes of the planets in the Solar System and several stars, including VV Cephei A:
1. Mercury < Mars < Venus < Earth
2. Earth < Neptune < Uranus < Saturn < Jupiter
3. Jupiter < Proxima Centauri < Sun < Sirius
4. Sirius < Pollux < Arcturus < Aldebaran
5. Aldebaran < Rigel < Antares < Betelgeuse
6. Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris.

The angular diameter of VV Cephei A can be estimated using photometric methods and has been calculated at 0.00638 arcseconds across.[9] This allows a direct calculation of the actual diameter, which is in good agreement with the 1,050 D derived from a complete orbital solution and eclipse timings. Observations of earlier eclipses had given diametrical values between 1,200 D and 1,600 D and an upper limit of 1,900 D.[19][7] The size of VV Cephei B is highly uncertain since it is physically and photometrically blocked by a much larger disc several hundred D in diameter. The secondary is definitely much smaller than both the primary or the disc, and has been calculated to have a diameter between 13 D to 25 D from the orbital solution.[7][15]

Despite VV Cephei A being an extremely large star (possibly the second largest known), showing high mass loss and having some emissions lines, it is not scientifically considered to be a hypergiant. The emission lines are produced from the accretion disc around the hot secondary and the absolute magnitude is typical for a normal red supergiant.[20]

References[edit]

  1. 1.0 1.1 1.2 1.3 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 2.0 2.1 2.2 2.3 2.4 Hopkins, Jeffrey L.; Bennett, Philip D.; Pollmann, Ernst (2015). "VV Cephei Eclipse Campaign 2017/19". The Society for Astronomical Sciences 34th Annual Symposium on Telescope Science. Published by Society for Astronomical Sciences 34: 83. Bibcode 2015SASS...34...83H.
  3. 3.0 3.1 Samus, N. N.Expression error: Unrecognized word "etal". (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.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 Graczyk, D.; Mikolajewski, M.; Janowski, J. L. (1999). "The Sudden Period Change of VV Cephei". Information Bulletin on Variable Stars 4679: 1. Bibcode 1999IBVS.4679....1G.
  5. Bauer, W. H.; Bennett, P. D.; Brown, A. (2007). "An Ultraviolet Spectral Atlas of VV Cephei during Total Eclipse". Astrophysical Journal Supplement Series 171 (1): 249–259. Bibcode 2007ApJS..171..249B. doi:10.1086/514334.
  6. Ginestet, N.; Carquillat, J. M. (2002). "Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components". The Astrophysical Journal Supplement Series 143 (2): 513. Bibcode 2002ApJS..143..513G. doi:10.1086/342942.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 Wright, K. O. (1977). "The system of VV Cephei derived from an analysis of the H-alpha line". Journal of the Royal Astronomical Society of Canada 71: 152. Bibcode 1977JRASC..71..152W.
  8. 8.0 8.1 8.2 Bennett, P. D.; Brown, A.; Fawcett, S. M.; Yang, S.; Bauer, W. H. (2004). "Fundamental parameters of intermediate and high mass stars". In Spectroscopically and Spatially Resolving the Components of the Close Binary Stars 318: 222. Bibcode 2004ASPC..318..222B.
  9. 9.0 9.1 9.2 9.3 Bauer, W. H.; Gull, T. R.; Bennett, P. D. (2008). "Spatial Extension in the Ultraviolet Spectrum of Vv Cephei". The Astronomical Journal 136 (3): 1312. Bibcode 2008AJ....136.1312H. doi:10.1088/0004-6256/136/3/1312.
  10. 10.0 10.1 Cite error: Invalid <ref> tag; no text was provided for refs named late
  11. Ridpath & Tirion 2001, pp. 112–113.
  12. Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal 628 (2): 973. arXiv:astro-ph/0504337. Bibcode 2005ApJ...628..973L. doi:10.1086/430901.
  13. Bennett, Philip D.; Bauer, Wendy Hagen (2015). "The Special Case of VV Cephei". Giants of Eclipse: the ζ Aurigae Stars and Other Binary Systems. Astrophysics and Space Science Library 408: 85. Bibcode 2015ASSL..408...85B. doi:10.1007/978-3-319-09198-3_3. ISBN 978-3-319-09197-6.
  14. 14.0 14.1 Carr, John S.; Sellgren, K.; Balachandran, Suchitra C. (2000). "The First Stellar Abundance Measurements in the Galactic Center: The M Supergiant IRS 7". The Astrophysical Journal 530: 307. arXiv:astro-ph/9909037. Bibcode 2000ApJ...530..307C. doi:10.1086/308340.
  15. 15.0 15.1 Hack, M.; Engin, S.; Yilmaz, N.; Sedmak, G.; Rusconi, L.; Boehm, C. (1992). "Spectroscopic study of the atmospheric eclipsing binary VV Cephei". Astronomy and Astrophysics Supplement Series (ISSN 0365-0138) 95: 589. Bibcode 1992A&AS...95..589H.
  16. Ramírez, Solange V.; Sellgren, K.; Carr, John S.; Balachandran, Suchitra C.; Blum, Robert; Terndrup, Donald M.; Steed, Adam (2000). "Stellar Iron Abundances at the Galactic Center". The Astrophysical Journal 537: 205. arXiv:astro-ph/0002062. Bibcode 2000ApJ...537..205R. doi:10.1086/309022.
  17. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society 410: 190. arXiv:1007.4883. Bibcode 2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
  18. Cite error: Invalid <ref> tag; no text was provided for refs named bauer2000
  19. Table 4 in Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal 628 (2): 973. arXiv:astro-ph/0504337. Bibcode 2005ApJ...628..973L. doi:10.1086/430901.
  20. Habets, G. M. H. J.; Heintz, J. R. W. (1981). "Empirical bolometric corrections for the main-sequence". Astronomy and Astrophysics Supplement Series 46: 193–237. Bibcode 1981A&AS...46..193H.


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Preceded by
Betelgeuse
Largest known star
2001—2007[citation needed]

1,600-1,900 R☉

Succeeded by
VY Canis Majoris
<<< 1. VY Canis Majoris 3. UY Scuti >>>