18 Delphini b

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18 Delphini b
Exoplanet List of exoplanets
Parent star
Star 18 Delphini
Constellation Delphinus
Right ascension (α) 20h 58m 26s
Declination (δ) +10° 50′ 21″
Apparent magnitude (mV) 5.52
Distance238 ± 11 ly
(73.1 ± 3.5 pc)
Spectral type G6III
Orbital elements
Semi-major axis(a) 2.6 AU
(390 Gm)
    35 mas
Periastron (q) 2.4 AU
(360 Gm)
Apastron (Q) 2.8 AU
(420 Gm)
Eccentricity (e) 0.08 ± 0.01
Orbital period(P) 993.3 ± 3.2 d
(2.719 y)
Argument of
(ω) 166.1 ± 6.5°
Time of periastron (T0) 2451672 ± 18 JD
Physical characteristics
Minimum mass(m sin i)10.3 MJ
Discovery information
Discovery date 19 February 2008
Discoverer(s) Sato et al.[1]
Discovery method radial velocity
Discovery site Okayama Planet
Search Program

Discovery status Published[1]
Other designations
Arion, HD 199665 b, HIP 103527 b, HR 8030 b
Database references
Extrasolar Planets
Exoplanet Archivedata
Open Exoplanet Cataloguedata

18 Delphini b (abbreviated 18 Del b), also named Arion, is an extrasolar planet approximately 238 light-years away in the constellation of Delphinus.

The 993-day period planet orbits the yellow giant star 18 Delphini. A very massive and dense planet with a minimum mass of 10.3 MJ it was discovered on February 19, 2008 by Sato.[1]

In July 2014 the International Astronomical Union launched a process for giving proper names to certain exoplanets and their host stars.[2] The process involved public nomination and voting for the new names.[3] In December 2015, the IAU announced the name Arion for this planet.[4] The winning name was submitted by the Tokushima Prefectural Jonan High School Science Club of Japan. Arion was a genius of poetry and music in ancient Greece. According to legend, his life was saved at sea by dolphins after attracting their attention by the playing of his kithara [5] ('Delphinus' is Latin for 'dolphin').

Radial velocity changes over time of 18 Delphini caused by the orbit of 18 Delphini b.

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Coordinates: Sky map 20h 58m 26s, +10° 50′ 21″