Epsilon Fornacis

Epsilon Fornacis
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Fornax
Right ascension	03h 42m 14.90248s
Declination	−31° 56′ 18.1055″
Apparent magnitude (V)	5.89
Characteristics
Spectral type	K2 V Fe-1.3 CH-0.8
B−V color index	+0.79
Astrometry
Radial velocity (Rv)	42.71±0.10 km/s
Proper motion (μ)	RA: 271.744 ± 0.111 mas/yr ; Dec.: -442.885 ± 0.121 mas/yr
Parallax (π)	31.2461 ± 0.0919 mas
Distance	104.4 ± 0.3 ly ; (32.00 ± 0.09 pc)
Absolute magnitude (MV)	+3.34
Orbit
Period (P)	13,770±3,528 d
Semi-major axis (a)	13±4 au
Eccentricity (e)	0.28±0.07
Periastron epoch (T)	2450865±9 JD
Argument of periastron (ω); (secondary)	314±34°
Semi-amplitude (K1); (primary)	3,112±1,903 km/s
Details
ε For A
Mass	0.91±0.02 M☉
Radius	2.53±0.07 R☉
Luminosity	4.5 L☉
Surface gravity (log g)	3.65±0.09 cgs
Temperature	5,068±39 K
Metallicity [Fe/H]	−0.61±0.04 dex
Rotational velocity (v sin i)	1.12±0.23 km/s
Age	> 12 Gyr
ε For B
Mass	> 0.42±0.10 M☉
Other designations
	ε For, FK5 2215, HD 18907, HIP 14086, HR 914, SAO 168238.
Database references
SIMBAD	data

ε Fornacis (Latinised as Epsilon Fornacis) is the Bayer designation for a high proper motion binary star^[7] in the southern constellation of Fornax. It is faintly visible to the naked eye with an apparent visual magnitude of 5.89.^[2] Based upon an annual parallax shift of 31.06 mas, the system is located roughly 105 light years from the Sun.^[1] At that distance, its visual magnitude is reduced by an interstellar absorption factor of 0.09 due to dust.^[8]

This is an astrometric binary star system. The best fit to the radial velocity data yields an orbital period of roughly 13,770 days (37.7 years) with an eccentricity of around 0.28. The semimajor axis of their computed orbit is about 13 au, or 13 times the distance of the Earth from the Sun.^[7] The primary, component A, is an evolved K-type subgiant star^[8] with a stellar classification of K2 V Fe-1.3 CH-0.8,^[3] where the suffix notation indicates the absorption lines of iron and the carbon-hydrogen bond are abnormally weak.^[10] However, classifications earlier than Gray et al. (2006) consistently showed it as type G5 IV,^[7] matching the subgiant categorization.

The primary has an estimated 91% of the Sun's mass, but has expanded to 253% times the Sun's radius. It has a quiet (inactive) chromosphere and is most likely an old star with an age over 12 billion years.^[7] The star is spinning slowly with a projected rotational velocity of 1.1 km/s.^[8] Since leaving the main sequence, it has increased in luminosity to 4.5 times that of the Sun, which is being radiated from its outer atmosphere at an effective temperature of 5,068 K.^[8]

Based upon its estimated orbit, the secondary, component B, has at least 42%±10% times of the Sun's mass.^[7]

References

^ ^a ^b ^c 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 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.
^ ^a ^b Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
^ 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 Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
^ 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, S2CID 119257644.
^ ^a ^b ^c ^d ^e ^f ^g Jenkins, J. S.; et al. (October 2015), "The observed distribution of spectroscopic binaries from the Anglo-Australian Planet Search", Monthly Notices of the Royal Astronomical Society, 453 (2): 1439–1457, arXiv:1507.04749, Bibcode:2015MNRAS.453.1439J, doi:10.1093/mnras/stv1596.
^ ^a ^b ^c ^d ^e Jofré, E.; et al. (2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets". Astronomy & Astrophysics. 574: A50. arXiv:1410.6422. Bibcode:2015A&A...574A..50J. doi:10.1051/0004-6361/201424474. S2CID 53666931.
^ "eps For -- High proper-motion Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-01-21.
^ Keenan, P. C. (1985), "The MK classification and its calibration", Proceedings of the Symposium, calibration of fundamental stellar quantities, vol. 111, Dordrecht: D. Reidel Publishing Co., pp. 121−135, Bibcode:1985IAUS..111..121K.