Iota Herculis

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ι Herculis
Location of ι Herculis (circled in red)
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 17h 39m 27.8864s[1]
Declination +46° 00′ 22.795″[1]
Apparent magnitude (V) 3.80[2]
Characteristics
Spectral type B3IV[1]
U−B color index −0.71
B−V color index −0.18[3]
Variable type Beta Cephei[4]
Astrometry
Radial velocity (Rv)−21.23±0.20[5] km/s
Proper motion (μ) RA: +7.48[6] mas/yr
Dec.: +4.53[6] mas/yr
Parallax (π)7.17±0.13 mas[6]
Distance455 ± 8 ly
(139 ± 3 pc)
Absolute magnitude (MV)−1.97[7]
Orbit[5]
Period (P)111.5±0.1 days
Semi-major axis (a)≥12.68±0.74 R☉
Eccentricity (e)0.53±0.03
Argument of periastron (ω)
(secondary)		208.3+5.2
−5.0°
Semi-amplitude (K1)
(primary)		6.8+0.4
−0.3 km/s
Details
Mass5.40+0.12
−0.08[5] M☉
Radius4.74±0.34[8] R☉
Luminosity2,489[2] L☉
Surface gravity (log g)3.61±0.02[5] cgs
Temperature14,346+104
−96[5] K
Metallicity [Fe/H]−0.40[9] dex
Rotational velocity (v sin i)6±1[2] km/s
Age37.8±8.6[10] Myr
Other designations
ι Her, 85 Her, HR 6588, BD+46°2349, HD 160762, FK5 663, HIP 86414, SAO 46872, GC 23965, CCDM J17395+4601A
Database references
SIMBADdata

Iota Herculis (ι Herculis, ι Her) is a fourth-magnitude binary star in the constellation Hercules, 139 parsecs (450 light-years) away. The brightest is a β Cephei variable, a pulsating star.

Visibility

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Small white disks representing the northern stars on a black background, overlaid by a circle showing the position of the north pole over time
The path of the north celestial pole among the stars due to the precession. Vega is the brightest star near the bottom, Iota Herculis is to the right near the −10,000 hatch mark.

Iota Herculis is dim enough that in cities with a lot of light pollution it is unlikely to be visible with the naked eye. In rural areas it will usually be visible, and for much of the Northern Hemisphere the star is circumpolar and visible year around.

Pole star

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As a visible star, the proximity of Iota Herculis to the precessional path the Earth's North Pole traces across the celestial sphere makes it a pole star, a title currently held by Polaris. In 10,000 BCE it was the pole star, and in the future it will be again. While Polaris is only 0.5° off the precessional path Iota Herculis is 4° off.

Preceded by Pole star Succeeded by
Vega ~16,000 CE Tau Herculis

Properties

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Iota Herculis is a spectroscopic binary having an orbital period of 111.5 days and a semi-major axis of at least 0.0590 au. The orbit is somewhat eccentric, at e = 0.53. Nothing is known about the companion.[5]

A light curve for Iota Herculis, plotted from TESS data.[11] The 3.487 day period[12] is marked in red.

The primary component is a B-type subgiant star that is at the end of its hydrogen fusion stage.[13] With a stellar classification B3IV,[1] it is considerably larger than the Sun, having a mass that is 5.4 times solar[5] and a radius 4.7 times. Though its apparent magnitude is only 3.80, it is 2,500 times more luminous than the Sun, yielding an absolute magnitude of −2.11, brighter in fact than most of the hot B stars in the Pleiades open star cluster. The Hipparcos satellite mission estimated its distance at roughly 152 parsecs (pc) from Earth, or 496 light-years (ly) away;[14] an updated parallax measurement from Floor van Leeuwen in 2007, however, puts the distance at 455 ly with a much tighter error factor of only 8 ly.[6]

A companion at a separation of about 30 au from Iota Herculis has been reported at the Washington Double Star Catalog, but it has been observed only once and is considered unconfirmed.[5] Another star has been identified with a common proper motion at an angular separation of 116 arcseconds and a visual magnitude of 12.1.[15] This would place it approximately 18,000 AU away, giving it an orbit of about 1 million years.[13] However, measurements by the Gaia spacecraft found it to be much farther away than Iota, and thus is not a member of the system.[5]

Etymology

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In Chinese, 天棓 (Tiān Bàng), meaning Celestial Flail, refers to an asterism consisting of ι Herculis, ξ Draconis, ν Draconis, β Draconis and γ Draconis.[16] Consequently, ι Herculis itself is known as 天棓五 (Tiān Bàng wu, English: the Fifth Star of Celestial Flail).

References

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  1. ^ a b c d "V* iot Her -- Variable Star of beta Cep type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-06-29.
  2. ^ a b c Szewczuk, W.; Daszyńska-Daszkiewicz, J. (2015). "Identification of pulsational modes in rotating slowly pulsating B-type stars". Monthly Notices of the Royal Astronomical Society. 450 (2): 1585. arXiv:1504.04490. Bibcode:2015MNRAS.450.1585S. doi:10.1093/mnras/stv715.
  3. ^ Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data: 0. Bibcode:1986EgUBV........0M. origin: SIMBAD
  4. ^ 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: B/GCVS. Bibcode:2009yCat....102025S.
  5. ^ a b c d e f g h i Bätz, J.; Mugrauer, M.; Michel, K. -U.; Reichert, J.; Tschirschky, A.; Pietsch, L.; Edelmann, F.; Neuhäuser, R. (2025). "Radial Velocity Monitoring and Analysis of Gaia Astrometry of Selected Intermediate Mass Stars to Constrain Their Multiplicity Status". arXiv:2510.09772 [astro-ph.SR].
  6. ^ a b c d van Leeuwen, F. (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Retrieved 2010-11-21.
  7. ^ Huang, W.; et al. (2012). "A catalogue of Paschen-line profiles in standard stars". Astronomy & Astrophysics. 547: A62. arXiv:1210.7893. Bibcode:2012A&A...547A..62H. doi:10.1051/0004-6361/201219804. S2CID 119286159.
  8. ^ Gordon, Kathryn D.; et al. (2019). "Angular Sizes, Radii, and Effective Temperatures of B-type Stars from Optical Interferometry with the CHARA Array". The Astrophysical Journal. 873 (1): 91. Bibcode:2019ApJ...873...91G. doi:10.3847/1538-4357/ab04b2. S2CID 125181833.
  9. ^ Peters, Geraldine J.; Aller, Lawrence H. (1970). "The Chemical Composition of IOTA Herculis". The Astrophysical Journal. 159: 525. Bibcode:1970ApJ...159..525P. doi:10.1086/150328.
  10. ^ 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:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
  11. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  12. ^ "iot Her". The International Variable Star Index. AAVSO. Retrieved 24 December 2024.
  13. ^ a b Kaler, James B. "IOTA HER (Iota Herculis)". Stars. University of Illinois. Retrieved 2010-06-29.
  14. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; et al. (1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49 – L52. Bibcode:1997A&A...323L..49P.
  15. ^ "CCDM (Catalog of Components of Double & Multiple stars (Dommanget+ 2002)". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-06-29.
  16. ^ (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.
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