V915 Scorpii

V915 Scorpii (HR 6392, HD 155603) is an orange hypergiant variable star in the constellation Scorpius.

V915 Scorpii

Position of V915 Scorpii (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Scorpius
Right ascension	17^h 14^m 27.65446^s[1]
Declination	−39° 45′ 59.9377″[1]
Apparent magnitude (V)	+6.22 - 6.64[2]
Characteristics
Spectral type	K0Ia-0[3]
U−B color index	2.48[4]
B−V color index	2.25[4]
Variable type	Unknown[2]
Astrometry
Radial velocity (Rv)	46.00[5] km/s
Proper motion (μ)	RA: −1,42[1] mas/yr Dec.: −1.47[1] mas/yr
Parallax (π)	−0.69 ± 0.77[1] mas
Distance	1,800[6] - 7,300[7] pc
Absolute magnitude (MV)	−9.0[8]
Details
Radius	760[lower-alpha 1] R☉
Luminosity	350,000[8] L☉
Surface gravity (log g)	0.0[9] cgs
Temperature	5,100[10] K
Metallicity [Fe/H]	+0.55[9] dex
Other designations
HR 6392, HD 155603, HIP 84322, CD−39°11212, IRAS 17109-3942, 2MASS J17142765-3945599, WDS J17145-3946
Database references
SIMBAD	data

Surroundings

V915 Scorpii and its companions resolved by the Hubble Space Telescope

V915 Scorpii is surrounded by the sparse OB association Moffat 2.[6] It is also surrounded by an envelope of dust and gas, producing a significant infrared excess.[10]

V915 Sco has been classified as a triple star. 15" away is the Wolf-Rayet star WR 85, one of the most luminous stars known, but still visually four magnitudes fainter than V915 Sco.[11] Component C is a 10th magnitude K class star 17" away.[12] There is also a 14th magnitude star 22" away. Photometry and space motions suggest that only V915 Sco and WR 85 lie at the same distance, while the other two stars are foreground objects. Assumptions about the brightness of each star suggest a distance of 2,600 parsecs, and a projected separation of 0.2 pc.[7]

Four arc minutes distant are two other assumed members of the association, a 10th magnitude B0 giant and an 11th magnitude OB star. Fitting the association members to a main sequence gives a highly uncertain distance of 1.8 kpc.[6] A kinematical distance has been calculated for the bubble around WR 85 at 2.8 kpc.[13] The distance to V915 Scorpii derived assuming minimal interstellar extinction is 7,300 pc.[10] However, the star is considerably reddened and this results in a distance of 2,630 pc.[7] Analysis of WR 85 as a luminous hydrogen-rich star gives a distance of 6,600 pc.[11]

Variable

V915 Scorpii is variable over nearly half a magnitude, but the nature of the variations is not known.[2][14] Any period associated with the variation is longer than 600 days.[15]

Properties

The distance to V915 Sco is highly uncertain, and it has hardly been observed in the last 20 years, but its absolute magnitude is consistently determined between −8 and −9, making it an extremely luminous supergiant.[6][8][10] The spectral type was assigned as G5Ia in 1954,[16] G5Ia-0 in 1973,[17] G8Ia in 1977,[6] K0Ia in 1982,[18] and K0Ia-0 in 1989.[3]

See also

• List of largest stars

References

1. 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. 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. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
4. 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.
5. Barbier-Brossat, M.; Petit, M.; Figon, P. (1994). "Third bibliographic catalogue of stellar radial velocities (Text in French)". Astronomy and Astrophysics Supplement Series. 108. Bibcode:1994A&AS..108..603B.
6. Moffat, A. F. J.; Fitzgerald, M. P. (1977). "Some very luminous supergiants associated with compact groups of luminous OB stars". Astronomy and Astrophysics. 54: 263. Bibcode:1977A&A....54..263M.
7. Andrews, J. P. (1977). "HR 6392 - A double star with very high luminosities". Monthly Notices of the Royal Astronomical Society. 178 (2): 131. Bibcode:1977MNRAS.178..131A. doi:10.1093/mnras/178.2.131.
8. Stickland, D. J. (1985). "IRAS observations of the cool galactic hypergiants". The Observatory. 105: 229. Bibcode:1985Obs...105..229S.
9. Luck, R. Earle; Bond, Howard E. (1989). "Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants". Astrophysical Journal Supplement Series. 71: 559. Bibcode:1989ApJS...71..559L. doi:10.1086/191386.
10. Odenwald, S. F. (1986). "An IRAS survey of IR excesses in G-type stars". Astrophysical Journal. 307: 711. Bibcode:1986ApJ...307..711O. doi:10.1086/164456.
11. Hamann, W.-R.; Gräfener, G.; Liermann, A. (2006). "The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation". Astronomy and Astrophysics. 457 (3): 1015. arXiv:astro-ph/0608078. Bibcode:2006A&A...457.1015H. doi:10.1051/0004-6361:20065052.
12. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
13. Vasquez, J.; Cappa, C.; McClure-Griffiths, N. M. (2005). "An HI interstellar bubble surrounding WR85 and RCW118". Monthly Notices of the Royal Astronomical Society. 362 (2): 681. arXiv:astro-ph/0507481. Bibcode:2005MNRAS.362..681V. doi:10.1111/j.1365-2966.2005.09349.x.
14. Dean, J. F. (1980). "BVRI Photometry of the Superluminous Supergiants HR 5171 and HR 6392". Information Bulletin on Variable Stars. 1796: 1. Bibcode:1980IBVS.1796....1D.
15. ESA (1997). "The HIPPARCOS and TYCHO catalogues. Astrometric and photometric star catalogues derived from the ESA HIPPARCOS Space Astrometry Mission". The Hipparcos and Tycho catalogues. Astrometric and photometric star catalogues derived from the ESA Hipparcos Space Astrometry Mission. 1200. Bibcode:1997ESASP1200.....E.
16. Bidelman, William P. (1954). "Spectral Classification of Southern Stars of High Luminosity". Publications of the Astronomical Society of the Pacific. 66: 249. Bibcode:1954PASP...66..249B. doi:10.1086/126709.
17. Warren, P. R. (1973). "A model atmosphere analysis of the super-supergiant HR 5171". Monthly Notices of the Royal Astronomical Society. 161 (4): 427. Bibcode:1973MNRAS.161..427W. doi:10.1093/mnras/161.4.427.
18. Houk, N. (1982). "Michigan Catalogue of Two-dimensional Spectral Types for the HD stars. Volume_3. Declinations -40_ƒ0 to -26_ƒ0". Michigan Catalogue of Two-dimensional Spectral Types for the HD stars. Volume_3. Declinations -40_ƒ0 to -26_ƒ0. Bibcode:1982mcts.book.....H.

Notes

1. Calculated from effective temperature and luminosity figures, with reference to the nominal solar temperature of 5,772 K: ${\displaystyle {\sqrt {(5772/5100)^{4}*350,000}}=757.79\ R\odot }$