HD 6718

HD 6718 is a solar twin^[10] star in the equatorial constellation of Cetus. It has a yellow hue but is too faint to be viewed with the naked eye, having an apparent visual magnitude of 8.45.^[2] The distance to this object, as determined from parallax measurements, is 168 light years. It is drifting away from the Sun with a radial velocity of +35 km/s.^[2]

HD 6718

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cetus
Right ascension	01h 07m 48.6630s[1]
Declination	–08° 14′ 01.3306″[1]
Apparent magnitude (V)	8.45[2]
Characteristics
Evolutionary stage	main sequence
Spectral type	G5V[3]
Apparent magnitude (B)	9.087[4]
Apparent magnitude (J)	7.269[5]
Apparent magnitude (H)	6.99[5]
Apparent magnitude (K)	6.876[5]
B−V color index	0.662±0.009[2]
Astrometry
Radial velocity (Rv)	+34.76[2] km/s
Proper motion (μ)	RA: 192.637±0.114[1] mas/yr Dec.: 20.080±0.069[1] mas/yr
Parallax (π)	19.4476 ± 0.0523 mas[1]
Distance	167.7 ± 0.5 ly (51.4 ± 0.1 pc)
Absolute magnitude (MV)	4.754[6]
Details
Mass	0.98±0.04[7] M☉
Radius	1.01±0.02[7] R☉
Luminosity	1.07±0.01[7] L☉
Surface gravity (log g)	4.42±0.02[8] cgs
Temperature	5,728±5[8] K
Metallicity [Fe/H]	−0.064±0.004[8] dex
Rotational velocity (v sin i)	2.00±0.12[8] km/s
Age	6.0±2.4[7] Gyr
Other designations
BD–09°221, HD 6718, HIP 5301, SAO 129137, PPM 183064, LTT 641, NLTT 3753[9]
Database references
SIMBAD	data
Exoplanet Archive	data

This object is an ordinary G-type main-sequence star with a stellar classification of G5V,^[3] with the luminosity class of 'V' indicating it is generating energy through hydrogen fusion at its core. It is around six billion years old with a leisurely rotation rate, having a projected rotational velocity of 2 km/s.^[8] The level of magnetic activity in the chromosphere is considered very low^[6] and it has a near solar metallicity.^[8] Being a solar twin, has nearly the same mass and radius as the Sun. The star is radiating 1.07^[7] times the luminosity of the Sun from its photosphere at an effective temperature of 5,728 K.^[8]

In 2009, a substellar companion (HD 6718 b) with a minimum mass of 1.56 M_J was found in orbit around the star with a period of 6.83 years.^[6] In 2020, the inclination of this object was measured, revealing its true mass to be 62.8 M_J. This makes it a brown dwarf.^[11]

The HD 6718 planetary system^[6][11]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	62.79+16.98 −13.80 MJ	3.56+0.24 −0.15	2496±176	0.10+0.11 −0.04	1.488+0.410 −0.310°	—

See also

• List of extrasolar planets

References

1. 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.
2. 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.
3. Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
4. Høg, E.; et al. (2000). The Tycho-2 catalogue of the 2.5 million brightest stars. Vol. 355. pp. L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862. ISBN 978-0333750889. {{cite book}}: |journal= ignored (help)
5. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; et al. (June 2003). "2MASS All Sky Catalog of point sources". The IRSA 2MASS All-Sky Point Source Catalog, NASA/IPAC Infrared Science Archive. Bibcode:2003tmc..book.....C.
6. Naef, Dominique; Mayor, Michel; Lo Curto, Gaspare; Bouchy, François; Lovis, Christophe; Moutou, Claire; Benz, Willy; Pepe, Francesco; Queloz, Didier; Santos, Nuno C.; Ségransan, Damien; Udry, Stéphane; Bonfils, Xavier; Delfosse, Xavier; Forveille, Thierry; Hébrard, Guillaume; Mordasini, Christoph; Perrier, Christian; Boisse, Isabelle; Sosnowska, Danuta (2010). "The HARPS Search for Southern Extrasolar Planets XXIII. 8 Planetary Companions to Low-activity Solar-type Stars". Astronomy and Astrophysics. 523: A15. arXiv:1008.4600. Bibcode:2010A&A...523A..15N. doi:10.1051/0004-6361/200913616. S2CID 118845989.
7. Bonfanti, A.; et al. (2015). "Revising the ages of planet-hosting stars". Astronomy and Astrophysics. 575. A18. arXiv:1411.4302. Bibcode:2015A&A...575A..18B. doi:10.1051/0004-6361/201424951. S2CID 54555839.
8. dos Santos, Leonardo A.; et al. (August 2016), "The Solar Twin Planet Search. IV. The Sun as a typical rotator and evidence for a new rotational braking law for Sun-like stars", Astronomy & Astrophysics, 592: 8, arXiv:1606.06214, Bibcode:2016A&A...592A.156D, doi:10.1051/0004-6361/201628558, S2CID 53533614, A156.
9. "HD 6718". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2014-09-08.
10. Ramírez, I.; et al. (December 2014). "The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample". Astronomy & Astrophysics. 572: 19. arXiv:1408.4130. Bibcode:2014A&A...572A..48R. doi:10.1051/0004-6361/201424244. S2CID 46964342. A48.
11. Kiefer, F.; et al. (January 2021). "Determining the true mass of radial-velocity exoplanets with Gaia. Nine planet candidates in the brown dwarf or stellar regime and 27 confirmed planets". Astronomy & Astrophysics. 645 A7. arXiv:2009.14164. Bibcode:2021A&A...645A...7K. doi:10.1051/0004-6361/202039168. S2CID 221995447.