Iota1 Scorpii

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For other stars with this Bayer designation, see ι Scorpii
Iota1 Scorpii
Diagram showing star positions and boundaries of the Scorpius constellation and its surroundings
Cercle rouge 100%.svg

Location of Iota1 Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 17h 47m 35.08113s[1]
Declination −40° 07′ 37.1893″[1]
Apparent magnitude (V) 3.03[2]
Spectral type F2 Ia[3]
U−B color index +0.26[2]
B−V color index +0.51[2]
Radial velocity (Rv) −27.6[4] km/s
Proper motion (μ) RA: +0.01[1] mas/yr
Dec.: −6.24[1] mas/yr
Parallax (π) 1.69 ± 0.15[1] mas
Distance 1,900 ± 200 ly
(590 ± 50 pc)
Mass 12.11 ± 0.66[5] M
Radius 125[6] to 400[7] R
Luminosity 35,070[5] L
Surface gravity (log g) 1.25[8] cgs
Temperature 7,000[8] K
Metallicity [Fe/H] 0.27[8] dex
Age 17.0 ± 0.5[9] Myr
Other designations
ι1 Sco, Iota-1 Scorpii, CD-40 11838, SAO 228420, FK5 666, HD 161471, HIP 87073, HR 6615.[10]

Iota1 Scorpii1 Scorpii) is star in the southern constellation of Scorpius. With an apparent visual magnitude of 3.03,[2] this star can be seen with the naked eye. It is sometimes called by the proper name Apollyon.[11] Parallax measurements place it at a distance of roughly 1,930 light-years (590 parsecs) from Earth, with a 9% margin of error.[1]

This star has a stellar classification of F2 Ia,[3] with the 'Ia' luminosity class indicating this is an evolved star that has expanded to become a supergiant. It has about 12 times the Sun's mass[5] and is radiating about 35,070 times the Sun's luminosity.[5] The radius is uncertain, with estimates ranging from 125[6] to 400[7] times that of the Sun. The effective temperature of the outer envelope is about 7,000 K,[8] which gives it a yellow-white hue typical of an F-type star.[12]

Iota1 Scorpii has a 10th magnitude companion at an angular separation of 37.5 arcseconds, which, at the distance of this star, gives it a projected separation of 20,000 Astronomical Units (AU). As the relative separation of the two stars along the line of sight to the Earth is not known, however, this distance represents only a minimum value for their separation.[6]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J 
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 2, Ann Arbor: Dept. of Astronomy, University of Michigan, 
  4. ^ Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W. 
  5. ^ a b c d Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335free to read, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355 
  6. ^ a b c Kaler, James B., "Iota-1 Scorpii", Stars, University of Illinois, retrieved 2012-01-12 
  7. ^ a b Pasinetti-Fracassini, L. E.; et al. (February 2001) [November 2000 (arXiv)], "Catalogue of Stellar Diameters (CADARS)", Astronomy and Astrophysics, 367: 521–524, arXiv:astro-ph/0012289free to read, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451 
  8. ^ a b c d Luck, R. E. (September 1979), "The chemical compositions of nine southern supergiant stars", Astrophysical Journal, Part 1, 232: 797–806, Bibcode:1979ApJ...232..797L, doi:10.1086/157340 
  9. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883free to read, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  10. ^ "HR 6615 -- Emission-line Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-12 
  11. ^ Moore, Patrick (2010), The Sky at Night, Patrick Moore's Practical Astronomy, Springer, p. 97, ISBN 1-4419-6408-8 
  12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16