HD 6718
Star in the constellation Cetus
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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.[1] 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]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cetus[1] |
| Right ascension | 01h 07m 48.66304s[2] |
| Declination | −08° 14′ 01.3307″[2] |
| Apparent magnitude (V) | 8.45[1] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| 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[1] |
| Astrometry | |
| Radial velocity (Rv) | +34.69±0.13[2] km/s |
| Proper motion (μ) | RA: +192.581 mas/yr[2] Dec.: +20.077 mas/yr[2] |
| Parallax (π) | 19.4544±0.0228 mas[2] |
| Distance | 167.7 ± 0.2 ly (51.40 ± 0.06 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) was found in orbit around the star with a period of 6.83 years. It has a minimum mass of 1.56 MJ, consistent with a gas giant planet.[6] In 2020, the inclination of this object was measured via astrometry, suggesting a true mass of 62.8 MJ, which would make it a brown dwarf.[11] However, a more recent astrometric study in 2026 found a much smaller true mass, again consistent with a planet.[12]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 2.4+0.3 −0.2 MJ |
3.53±0.05 | 2476±19 | 0.06±0.03 | 51.4+16.4 −11.5° |
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