99 Herculis

Last updated
99 Herculis
Observation data
Epoch J2000       Equinox J2000
Constellation Hercules
Right ascension 18h 07m 01.53971s [1]
Declination +30° 33′ 43.6896″ [1]
Apparent magnitude  (V)5.066 [2] (A: 5.10; B: 8.45) [3]
Characteristics
Spectral type F7 V [4] + K4 V [5]
U−B color index –0.056 [2]
B−V color index +0.548 [2]
Astrometry
Radial velocity (Rv)+1.7 [6] km/s
Proper motion (μ)RA: –100.32 [1] mas/yr
Dec.: +110.08 [1] mas/yr
Parallax (π)63.93±0.34  mas [1]
Distance 51.0 ± 0.3  ly
(15.64 ± 0.08  pc)
Absolute magnitude  (MV)4.08 [7]
Orbit [5]
Period (P)56.3±0.1  yr
Semi-major axis (a)1.06±0.02″
Eccentricity (e)0.766±0.004
Inclination (i)39±2°
Longitude of the node (Ω)41±2°
Periastron epoch (T)1997.62±0.05
Argument of periastron (ω)
(secondary)		116±2°
Details
99 Her A
Mass 1.14 [8]   M☉
Radius 1.34 [8]   R☉
Luminosity 1.90 [8]   L☉
Surface gravity (log g)4.17 [4]   cgs
Temperature 5,908 [8]   K
Metallicity [Fe/H]–0.60 [4]   dex
Rotational velocity (v sin i)5 [7]  km/s
Age 9.37 [4]   Gyr
99 Her B
Mass 0.46 [5]   M☉
Radius 0.67 [9]   R☉
Luminosity0.19 [10]   L☉
Temperature 4,449 [9]   K
Other designations
b Her, 99 Her, BD+30°3128, GJ 704, HD 165908, HIP 88745, HR 6775, SAO 66648 [11]
Database references
SIMBAD data
99 Her B

99 Herculis is the Flamsteed designation for a binary star system in the northern constellation of Hercules. It has the Bayer designation b Herculis, while 99 Herculis is the Flamsteed designation. This system has an apparent visual magnitude of 5.1, [2] which, according to the Bortle scale, makes it faintly visible to the naked eye from suburban skies. Measurements made with the Hipparcos spacecraft show an annual parallax shift of 0.064″, [1] corresponding to a physical distance of about 51.0 ly (15.6 pc) from the Sun. The system is moving further from the Earth with a heliocentric radial velocity of +1.7 km/s. [6]

Contents

The binary nature of this star system was first discovered in 1859 by English astronomer W. R. Dawes. [12] The two stellar components orbit around their common center of mass, or barycenter, with a period of 56.3 years and an eccentricity of 0.766. The semi-major axis of their orbit spans an angle of 1.06 arcseconds, which corresponds to a physical dimension of 16.5  AU. The plane of their orbit is inclined by an angle of about 39° to the line-of-sight from the Earth. Reports of a third component of this system now appear doubtful. [5]

System

The primary component, 99 Herculis A, is an F-type main sequence star with a stellar classification of F7 V. [4] It is 13% more mass than the Sun and nearly double the luminosity, but has an estimated 34% greater radius. The effective temperature of the star's outer atmosphere is 5,908  K , [8] giving it a white-hued glow. [13] This is a metal-poor star, showing overall abundances of elements—other than hydrogen or helium—equal to 60% of those in the Sun. [14]

The secondary component, 99 Herculis B, is fainter by 3.35 magnitudes compared to the primary. It is a K-type main sequence star with a classification of K4 V. [5] With 46% of the mass of the Sun, [5] it is 67% of the radius of the Sun [9] but shines with just 19% of the Sun's luminosity. [10]

Debris disk

Images from the Herschel Space Observatory show that a narrow disk of dusty debris is orbiting the barycenter at an average radius of 120 AU. Oddly, the disk appears to be misaligned with the orbital plane of the binary system and is instead aligned with the poles. This may be the result of an interaction within another star system some time in the past. Most of the disk emission appears to be caused by icy objects having a diameter of 10 cm or less, with a net mass of about ten times the mass of the Earth. [5]

It is hypothesized that the debris disk is being sculpted by several (likely two) polar circumbinary planets due to the disk being truncated in some regions. Simulations of this system that only have a single planet are insufficient to explain the morphology of the disk as that planet only truncates one edge of the disk leaving the other edge extended. Simulation that have two planets successfully model what is seen in the debris disk of 99 Herculis as they can carve out the disk on both edges leaving a narrow debris disk. [15]

References

  1. 1 2 3 4 5 6 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, S2CID   18759600.
  2. 1 2 3 4 Rakos, K. D.; et al. (February 1982), "Photometric and astrometric observations of close visual binaries", Astronomy and Astrophysics Supplement Series, 47: 221–235, Bibcode:1982A&AS...47..221R.
  3. ↑ Eggen, O. J. (February 1965), "Masses, luminosities, colors, and space motions of 228 visual binaries", Astronomical Journal, 70: 90, Bibcode:1965AJ.....70...19E, doi:10.1086/109676.
  4. 1 2 3 4 5 Maldonado, J.; et al. (May 2012). "Metallicity of solar-type stars with debris discs and planets". Astronomy & Astrophysics. 541: A40. arXiv: 1202.5884 . Bibcode:2012A&A...541A..40M. doi:10.1051/0004-6361/201218800. S2CID   46328823.
  5. 1 2 3 4 5 6 7 Kennedy, G. M.; et al. (April 2012), "99 Herculis: host to a circumbinary polar-ring debris disc", Monthly Notices of the Royal Astronomical Society , 421 (3): 2264–2276, arXiv: 1201.1911 , Bibcode:2012MNRAS.421.2264K, doi: 10.1111/j.1365-2966.2012.20448.x , S2CID   53710762.
  6. 1 2 Nordström, B.; et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14,000 F and G dwarfs", Astronomy and Astrophysics, 418 (3): 989–1019, arXiv: astro-ph/0405198 , Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959, S2CID   11027621.
  7. 1 2 Takeda, Yoichi; et al. (February 2005), "High-Dispersion Spectra Collection of Nearby F--K Stars at Okayama Astrophysical Observatory: A Basis for Spectroscopic Abundance Standards", Publications of the Astronomical Society of Japan, 57 (1): 13–25, Bibcode:2005PASJ...57...13T, doi: 10.1093/pasj/57.1.13 .
  8. 1 2 3 4 5 Hardegree-Ullman, Kevin K.; Apai, Dániel; Bergsten, Galen J.; Pascucci, Ilaria; López-Morales, Mercedes (2023). "Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O2 Levels in Nearby Transiting Habitable-zone Exoplanets". The Astronomical Journal. 165 (6): 267. arXiv: 2304.12490 . Bibcode:2023AJ....165..267H. doi: 10.3847/1538-3881/acd1ec .
  9. 1 2 3 Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de la Vieuville, Geoffroy; Butler, C. J.; Paletou, F. (2019). "The Mass-Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs". The Astronomical Journal. 158 (2): 56. arXiv: 1905.07921 . Bibcode:2019AJ....158...56H. doi: 10.3847/1538-3881/ab23fe .
  10. 1 2 Kral, Quentin; Matrà, Luca; Wyatt, Mark C.; Kennedy, Grant M. (2017). "Predictions for the secondary CO, C and O gas content of debris discs from the destruction of volatile-rich planetesimals". Monthly Notices of the Royal Astronomical Society. 469 (1): 521. arXiv: 1703.10693 . Bibcode:2017MNRAS.469..521K. doi: 10.1093/mnras/stx730 .
  11. ↑ "b Her". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2013-10-10.
  12. ↑ van Biesbroeck, G. (1947), "The orbit of 99 Herculis = Alvan Clark 15", Astronomical Journal, 53: 23–24, Bibcode:1947AJ.....53...23V, doi: 10.1086/106040 .
  13. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16.
  14. ↑ Adelman, Saul J.; et al. (August 2000), "Elemental abundance analyses with DAO spectrograms - XXIII. The superficially normal stars 28 And (A7III) and 99 Her (F7V)", Monthly Notices of the Royal Astronomical Society, 316 (3): 514–518, Bibcode:2000MNRAS.316..514A, doi: 10.1046/j.1365-8711.2000.03577.x .
  15. ↑ Smallwood, Jeremy L.; DeRocco, William; Qin, Zhizhen; Sefilian, Antranik A. (2025-10-09), The polar debris disc around 99 Herculis: A potential signpost for polar circumbinary planets, arXiv, doi:10.48550/arXiv.2510.08698, arXiv:2510.08698, retrieved 2026-01-08
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