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Phi Herculis
	; φ Herculis in optical light
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Hercules
Right ascension	16h 08m 46.17745s
Declination	+44° 56′ 05.6663″
Apparent magnitude (V)	4.24
Characteristics
Spectral type	B9VspHgMn + A8V
U−B color index	−0.23
B−V color index	−0.06
Variable type	α2 CVn?
Astrometry
Radial velocity (Rv)	−16.3±0.4 km/s
Proper motion (μ)	RA: −26.63 mas/yr ; Dec.: +36.76 mas/yr
Parallax (π)	15.99 ± 0.45 mas
Distance	204 ± 6 ly ; (63 ± 2 pc)
Absolute magnitude (MV)	A: 0.100 ± 0.059; B: 2.670 ± 0.074
Orbit
Period (P)	564.834±0.038 d
Semi-major axis (a)	32.027±0.028 mas
Eccentricity (e)	0.52614±0.00086
Inclination (i)	9.1±0.4°
Longitude of the node (Ω)	190.4±1.4°
Periastron epoch (T)	2450121.43 ± 0.20 JD
Argument of periastron (ω); (secondary)	350.3±1.4°
Semi-amplitude (K1); (primary)	2.772±0.073 km/s
Semi-amplitude (K2); (secondary)	8.1 km/s
Details
φ Her A
Mass	3.05±0.24 M☉
Luminosity	72 L☉
Surface gravity (log g)	4.05±0.15 cgs
Temperature	11,525±150 K
Metallicity [Fe/H]	−0.03 dex
Rotational velocity (v sin i)	8.0±1.0 km/s
Age	210 Myr
φ Her B
Mass	1.614±0.066 M☉
Surface gravity (log g)	4.30±0.15 cgs
Temperature	8,000±150 K
Rotational velocity (v sin i)	50.0±3.0 km/s
Other designations
	φ Her, 11 Her, BD+45°2376, FK5 601, HD 145389, HIP 79101, HR 6023, SAO 45911.
Database references
SIMBAD	data

Phi Herculis (φ Her) is a binary star^[4] system in the northern constellation of Hercules. Based upon an annual parallax shift of 15.99 mas as seen from Earth,^[1] it is located around 204 light years from the Sun. With a combined apparent visual magnitude of 4.24,^[2] it is bright enough to be seen with the naked eye.

A light curve for Phi Herculis, assuming a 3.708 day period,^[10] plotted from *TESS* data^[11]

This is a single-lined spectroscopic binary star system with an orbital period of 564.8 days and an eccentricity of 0.526.^[7] The primary, component A, is a B-type main sequence star with a stellar classification of B9VspHgMn.^[3] It is a chemically peculiar star of the type called a mercury-manganese star.^[4] The star is tentatively catalogued as an Alpha2 Canum Venaticorum variable, with brightness variations of just 0.01 magnitudes.^[5]^[12]

The secondary, component B, was first separated via interferometry in 2004.^[13] It is an A-type main sequence star of class A8V.^[4] The magnitude difference between the two components is 2.64.^[13]

References

^ ^a ^b ^c ^d ^e ^f van Leeuwen, F. (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.
^ ^a ^b ^c ^d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
^ ^a ^b Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Zavala, R. T.; et al. (February 2007), "The Mercury-Manganese Binary Star φ Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary", The Astrophysical Journal, 655 (2): 1046–1057, arXiv:astro-ph/0610811, Bibcode:2007ApJ...655.1046Z, doi:10.1086/510108, S2CID 118994617.
^ ^a ^b Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
^ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
^ ^a ^b ^c ^d ^e ^f ^g Torres, Guillermo (June 2007), "Astrometric-Spectroscopic Determination of the Absolute Masses of the HgMn Binary Star φ Herculis", The Astronomical Journal, 133 (6): 2684–2695, arXiv:astro-ph/0703193, Bibcode:2007AJ....133.2684T, doi:10.1086/516756, S2CID 11625161.
^ McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
^ "phi Her", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-04-05.
^ Kochukhov, O.; Khalack, V.; Kobzar, O.; Neiner, C.; Paunzen, E.; Labadie-Bartz, J.; David-Uraz, A. (October 2021), "TESS survey of rotational and pulsational variability of mercury–manganese stars", Monthly Notices of the Royal Astronomical Society, 506 (4): 5328–5344, arXiv:2107.09096, doi:10.1093/mnras/stab2107.
^ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, retrieved 8 December 2021.
^ Kazarovets, E. V.; et al. (1999), "The 74th Special Name-list of Variable Stars", Information Bulletin on Variable Stars, 4659 (4659): 1, Bibcode:1999IBVS.4659....1K.
^ ^a ^b Zavala, R. T.; et al. (December 2004), "Detection of the Secondary of the HgMn star Phi Herculis with the Navy Prototype Optical Interferometer", Bulletin of the American Astronomical Society, 36: 1527, Bibcode:2004AAS...20510715Z.