HD 168746

Coordinates: Sky map 18h 21m 49.7832s, −11° 55′ 21.660″
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HD 168746 / Alasia
Observation data
Epoch J2000      Equinox J2000
Constellation Serpens
Right ascension 18h 21m 49.783s[1]
Declination −11° 55′ 21.65″[1]
Apparent magnitude (V) 7.95[2]
Spectral type G5V[2]
B−V color index 0.713[2]
Radial velocity (Rv)25.606±0.0003[3] km/s
Proper motion (μ) RA: −22.963 mas/yr[1]
Dec.: −68.395 mas/yr[1]
Parallax (π)23.9884 ± 0.0259 mas[1]
Distance136.0 ± 0.1 ly
(41.69 ± 0.05 pc)
Absolute magnitude (MV)4.78[2]
Mass0.90±0.01[4] M
Radius1.07±0.01[4] R
Luminosity1.04±0.01[4] L
Surface gravity (log g)4.32±0.01[4] cgs
Temperature5,637±26[4] K
Metallicity [Fe/H]−0.06±0.05[2] dex
Rotation8.7 d[2]
Rotational velocity (v sin i)1.0[2] km/s
Age12.0±0.9 Gyr[4]
[5] Gyr
Other designations
Alasia, BD−11° 4606, HD 168746, HIP 90004, SAO 161386, PPM 234431[6]
Database references
Exoplanet Archivedata

HD 168746 is a Sun-like star with a close orbiting exoplanet in the constellation of Serpens. With an apparent visual magnitude of 7.95,[2] it is too faint to be viewed with the naked eye but is easily visible with binoculars or a small telescope. The distance to this system is 136 light years based on parallax measurements, and it is drifting further away from the Sun with a radial velocity of 25.6 km/s.[3]

This is an old G-type main-sequence star with a stellar classification of G5V.[2] The level of magnetic activity in the chromosphere is negligible.[2] It has just 90% of the mass of the Sun but a 7% larger radius. The star is radiating a 4% greater luminosity than the Sun from its photosphere at an effective temperature of 5,637 K.[4]

In 2019 the HD 168746 planetary system was chosen as part of the NameExoWorlds campaign organised by the International Astronomical Union to mark to 100th anniversary of the organisation. Each country was assigned a star and planet to be named with HD 168746 being assigned to Cyprus. The winning proposal named the star Alasia, an ancient name for Cyprus, and the planet Onasilos after an ancient Cypriot physician identified in the Idalion Tablet, one of the oldest known legal contracts.

Planetary system[edit]

In 2006, the exoplanet HD 168746 b was discovered by Exoplanet group at the Geneva Observatory with the radial velocity method using the CORALIE spectrograph on the Swiss 1.2-metre Leonard Euler Telescope.[2][7] At the time it was one of the lowest minimum mass planets that had been discovered.

The HD 168746 planetary system[2]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (Onasilos) >0.23 MJ 0.065 6.403 ± 0.001 0.081 ± 0.029

See also[edit]


  1. ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b c d e f g h i j k l Pepe, F.; et al. (2002). "The CORALIE survey for southern extra-solar planets VII. Two short-period Saturnian companions to HD 108147 and HD 168746". Astronomy and Astrophysics. 388 (2): 632–638. arXiv:astro-ph/0202457. Bibcode:2002A&A...388..632P. doi:10.1051/0004-6361:20020433. S2CID 13942987.
  3. ^ 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.
  4. ^ a b c d e f g Bonfanti, A.; Ortolani, S.; Nascimbeni, V. (2016). "Age consistency between exoplanet hosts and field stars". Astronomy & Astrophysics. 585: 14. arXiv:1511.01744. Bibcode:2016A&A...585A...5B. doi:10.1051/0004-6361/201527297. S2CID 53971692. A5.
  5. ^ Chen, Xunzhou; et al. (February 2020). "Ages of Dwarfs in the Solar Neighborhood: Considering C and O Enhancements". The Astrophysical Journal. 889 (2): 157. Bibcode:2020ApJ...889..157C. doi:10.3847/1538-4357/ab66c7. 157.
  6. ^ "HD 168746". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-04-05.
  7. ^ "Exoplanets Galore!" (Press release). Garching, Germany: European Southern Observatory. April 15, 2000. Retrieved December 30, 2012.