Phi Herculis

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.

Phi Herculis

φ Herculis in optical light
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hercules
Right ascension  16h 08m 46.17745s[1]
Declination +44° 56′ 05.6663″[1]
Apparent magnitude (V) 4.24[2]
Characteristics
Spectral type B9VspHgMn[3] + A8V[4]
U−B color index −0.23[2]
B−V color index −0.06[2]
Astrometry
Radial velocity (Rv)−16.3±0.4[5] km/s
Proper motion (μ) RA: −26.63[1] mas/yr
Dec.: +36.76[1] mas/yr
Parallax (π)15.99 ± 0.45[1] mas
Distance204 ± 6 ly
(63 ± 2 pc)
Absolute magnitude (MV)A: 0.100 ± 0.059
B: 2.670 ± 0.074[6]
Orbit[6]
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[4] km/s
Details
φ Her A
Mass3.05±0.24[6] M☉
Luminosity72[7] L☉
Surface gravity (log g)4.05±0.15[4] cgs
Temperature11,525±150[4] K
Metallicity [Fe/H]−0.03[6] dex
Rotational velocity (v sin i)8.0±1.0[4] km/s
Age210[6] Myr
φ Her B
Mass1.614±0.066[6] M☉
Surface gravity (log g)4.30±0.15[4] cgs
Temperature8,000±150[4] K
Rotational velocity (v sin i)50.0±3.0[4] km/s
Other designations
φ Her, 11 Her, BD+45° 2376, FK5 601, HD 145389, HIP 79101, HR 6023, SAO 45911.[8]
Database references
SIMBADdata

This is a single-lined spectroscopic binary star system with an orbital period of 564.8 days and an eccentricity of 0.526.[6] 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 cataloged as an Alpha2 Canum Venaticorum variable.[9]

The secondary, component B, was first separated via interferometry in 2004.[10] It is an A-type main sequence star of class A8V.[4] The magnitude difference between the two components is 2.64.[10]

References
  1. 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.
  2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. 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.
  4. 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.
  5. 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, A61.
  6. 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.
  7. 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.
  8. "phi Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-04-05.
  9. Kazarovets, E. V.; et al. (1999), "The 74th Special Name-list of Variable Stars", Information Bulletin on Variable Stars (4659), Bibcode:1999IBVS.4659....1K.
  10. 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.
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