Omicron Herculis

Omicron Herculis, Latinized from o Herculis, is a multiple star system in the constellation Hercules. It used to be called Masym ("the wrist"), but this name was transferred to Lambda Herculis.[9]

o Herculis
Hercules constellation map.svg
Red circle.svg
Location of o Herculis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 18h 07m 32.55073s[1]
Declination +28° 45′ 44.9679″[1]
Apparent magnitude (V) 3.83[2]
Spectral type B9.5 V[3]
U−B color index –0.07[2]
B−V color index –0.02[2]
Variable type γ Cas[4]
Radial velocity (Rv)–29.5[5] km/s
Proper motion (μ) RA: –0.02[1] mas/yr
Dec.: +8.55[1] mas/yr
Parallax (π)9.65 ± 0.16[1] mas
Distance338 ± 6 ly
(104 ± 2 pc)
Absolute magnitude (MV)−1.24[6]
Mass3.49±0.04 M
Luminosity355 L
Temperature9,484 K
Metallicity [Fe/H]−0.06[6] dex
Rotational velocity (v sin i)194[8] km/s
Other designations
o Her, 103 Herculis, BD+28 2925, FK5 681, HD 166014, HIP 88794, HR 6779, SAO 85750.
Database references


Omicron Herculis is a B9.5V star approximately 106 pc from the Earth. It has an apparent magnitude of 3.83. The star radiates with a bluish-white hue, and has a luminosity approximately 355 times as bright as the Sun. Omicron Herculis is 3.49 solar masses.[7]

Omicron Herculis is an eruptive variable of the Gamma Cassiopeiae class,[4] which are rapidly rotating B-class stars with mass outflow. It has a projected rotational velocity of 194 km/s.[8]

Omicron Herculis is both a spectroscopic and an interferometric binary star with a separation of 0.1 arcsec.

Omicron Hercules is notable for residing close to the coordinates of the solar apex, the direction towards which the Sun is moving. This was first noticed by William Herschel in 1783,[10] although in his first calculation he identified this point with Lambda Herculis.[11] It will eventually become the brightest star in the sky in approximately 3 million years from today, at -0.4, slightly less bright than Canopus today.[citation needed]


  1. ^ a b c d e 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.
  2. ^ a b c 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. ^ Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819
  4. ^ a b Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085.
  5. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
  6. ^ a b Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  7. ^ a b Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691.
  8. ^ a b Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
  9. ^ Kaler, Jim. "Omicron Herculis". Retrieved 2016-05-13.
  10. ^ Lankford, John (1997). History of astronomy: an encyclopedia. Garland encyclopedias in the history of science. 1. Taylor & Francis. p. 258. ISBN 0-8153-0322-X.
  11. ^ Herschel, William (1783). "On the Proper Motion of the Sun and Solar System; With an Account of Several Changes That Have Happened among the Fixed Stars since the Time of Mr. Flamstead [sic]". Philosophical Transactions of the Royal Society of London. 73: 247–83. doi:10.1098/rstl.1783.0017. JSTOR 106492.

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