HD 218566

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HD 218566 / Ebla
Observation data
Epoch J2000      Equinox J2000
Constellation Pisces
Right ascension 23h 09m 10.72701s[1]
Declination −02° 15′ 38.6854″[1]
Apparent magnitude (V) 8.628[2]
Spectral type K3 V[3]
B−V color index 1.014[3]
Radial velocity (Rv)−37.800±0.0029[4] km/s
Proper motion (μ) RA: +631.520[1] mas/yr
Dec.: −97.214[1] mas/yr
Parallax (π)34.6603 ± 0.0511 mas[1]
Distance94.1 ± 0.1 ly
(28.85 ± 0.04 pc)
Absolute magnitude (MV)6.187[3]
Mass0.81±0.06[5] M
Radius0.86±0.08[2] R
Luminosity0.353±0.032[2] L
Surface gravity (log g)4.48±0.04[5] cgs
Temperature4,849±42[5] K
Metallicity [Fe/H]0.38[3] dex
Rotational velocity (v sin i)0.0 km/s
Age8.5[2] to 11.5[5] Gyr
Other designations
Ebla[6][7], BD−03°5577, HD 218566, HIP 114322, SAO 146533[8]
Database references

HD 218566 is a star in the equatorial zodiac constellation of Pisces. It has the proper name Ebla, after a kingdom in ancient Syria. With an apparent visual magnitude of 8.6,[2] this ninth magnitude star can not be viewed with the naked eye. However, it can be readily seen even with a small telescope.[9] It is located at a distance of 94 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −37.8 km/s.[4] The star hosts one known exoplanet, HD 218566 b.[2]


The name Ebla was selected in the NameExoWorlds campaign by Syria, during the 100th anniversary of the IAU. Ebla was one of the earliest kingdoms in Syria. At this time, the planet HD 218566 b was named Ugarit. Ugarit was a city where its scribes devised the Ugaritic alphabet around 1400 B.C.[6][7]

Stellar properties[edit]

HD 218566 is a smaller star than the Sun, with about 81%[5] of the Sun's mass and 86% of the radius of the Sun.[2] It is a K-type main sequence star with a stellar classification of K3 V[3] that is generating energy by the nuclear fusion of hydrogen at its core. HD 218556 is radiating around 35% of the luminosity of the Sun from its outer envelope at an effective temperature of 4,849 K.[5] This heat gives the star the characteristic orange-hued glow of a K-type star.[10]

Compared to the Sun, this star has an unusually high abundance of elements other than hydrogen and helium, what astronomers term the metallicity. Based upon the abundance of iron, the metallicity is 2.4 times as high as in the Sun.[2] It is much older than the Sun, with estimates of its age ranging from 8.5[2] to 11.5[5] billion years. It appears to have a negligible rate of spin as its projected rotational velocity is too small to measure.[2]

This star belongs to the thick disk population of the Milky Way. In the galactic coordinate system, it has space velocity components of [U, V, W] = [77, −61, −8] km/s. HD 218556 is following an orbit through the galaxy with an eccentricity of 0.36±0.01 that carries it as close as 14.3 kly (4.4 kpc) and as far as 30.3 kly (9.3 kpc) from the Galactic Center. The orbital tilt carries this star as much as 0.6 kly (0.18 kpc) from the galactic plane.[5]

Planetary system[edit]

Based upon high resolution measurements performed at the W. M. Keck Observatory and analysis performed upon these measurements by amateur astronomer Peter Jalowiczor, HD 218566 shows cyclical variations in radial velocity that suggest gravitational perturbation by orbiting companion. This candidate object is estimated to be orbiting the parent star with a period of 225.7±0.4 days at an eccentricity of 0.3±0.1. The semi-major axis for this Keplerian orbit is an estimated 0.6873 astronomical units. Because the inclination of the orbit remains unknown, the mass of this companion has not been determined. However, it can be constrained to have a mass of at least 21% the mass of Jupiter. There is no evidence of additional companions in the system.[2]

The HD 218566 planetary system[11]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b / Ugarit ≥0.198±0.018 MJ 0.6875+0.0081


  1. ^ a b c d e 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. ^ a b c d e f g h i j k Meschiari, Stefano; et al. (February 2011), "The Lick-Carnegie Survey: Four New Exoplanet Candidates", The Astrophysical Journal, 727 (2): 117, arXiv:1011.4068, Bibcode:2011ApJ...727..117M, doi:10.1088/0004-637X/727/2/117, S2CID 59065004
  3. ^ a b c d e Soubiran, C.; et al. (2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788, S2CID 16602121
  4. ^ a b Soubiran, C.; et al. (2018), "Gaia Data Release 2. The catalogue of radial velocity standard stars", Astronomy and Astrophysics, 616: A7, arXiv:1804.09370, Bibcode:2018A&A...616A...7S, doi:10.1051/0004-6361/201832795, S2CID 52952408
  5. ^ a b c d e f g h Trevisan, M.; et al. (November 2011), "Analysis of old very metal rich stars in the solar neighbourhood", Astronomy & Astrophysics, 535: A42, arXiv:1109.6304, Bibcode:2011A&A...535A..42T, doi:10.1051/0004-6361/201016056, S2CID 49565866. See table 13.
  6. ^ a b "Approved names". NameExoworlds. Retrieved 2020-01-02.
  7. ^ a b "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
  8. ^ "HD 218566". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-11-27.
  9. ^ Sherrod, P. Clay; Koed, Thomas L. (2003), A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations, Astronomy Series, Courier Dover Publications, p. 9, ISBN 0-486-42820-6
  10. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
  11. ^ "HD 218566". NASA Exoplanet Archive. Retrieved 26 April 2023.