| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Delphinus |
| Right ascension | 20h 58m 25.9336s[1] |
| Declination | +10° 50′ 21.4261″[1] |
| Apparent magnitude (V) | 5.506[2] |
| Characteristics | |
| Spectral type | G6III[3] |
| B−Vcolor index | 0.934±0.004[4] |
| Astrometry | |
| Radial velocity (Rv) | +4.35±0.15[1] km/s |
| Proper motion (μ) | RA: −50.034±0.147[1]mas/yr Dec.: −34.198±0.175[1]mas/yr |
| Parallax (π) | 13.0922±0.1062 mas[1] |
| Distance | 249 ± 2 ly (76.4 ± 0.6 pc) |
| Absolute magnitude (MV) | 1.15[5] |
| Details[6] | |
| Mass | 2.35±0.07 M☉ |
| Radius | 7.19±0.38 R☉ |
| Luminosity | 33.9+6.9 −5.7 L☉ |
| Surface gravity (log g) | 3.00±0.04 cgs |
| Temperature | 5,071±10 K |
| Metallicity [Fe/H] | 0.10±0.02 dex |
| Rotational velocity (v sin i) | 1.60±0.45 km/s |
| Age | 690±50 Myr |
| Other designations | |
| Musica,18 Del,BD+10°4425,GC 29266,HD 199665,HIP 103527,HR 8030,SAO 106712,WDS J20584+1050A[7] | |
| Database references | |
| SIMBAD | data |
18 Delphini, also namedMusica/ˈmjuːzɪkə/,[8][9] is a single[10]star in theconstellation ofDelphinus of the low northern hemisphere. It has a Sun-like golden hue and is faintly visible to the naked eye with anapparent visual magnitude of 5.506.[2] The star is located at a distance of approximately 249 light years from theSun based onparallax,[1] and it is drifting further away with aradial velocity of +4 km/s.[1] An object believed to be anextrasolar planet (designated18 Delphini b or Arion) orbits the star.[5]
18 Delphini is the star'sFlamsteed designation, abbreviated 18 Del. Following its discovery the planet was designated 18 Delphini b.[5]
As part of theNameExoWorlds program by theInternational Astronomical Union, in 2015 the name Musica,Latin for 'music', was selected for this star by Tokushima Prefectural Jonan High School Science Club ofJapan. The planet was given the nameArion,[11] after a genius of poetry and music in ancient Greece. According to legend, his life was saved at sea bydolphins after attracting their attention by the playing of hiskithara. The constellation 'Delphinus' is Latin for 'dolphin'.[12][8]
Thestellar classification of 18 Delphini is G6III,[3] which means it is anevolved star that has cooled and expanded off themain sequence. It is a suspectedred clump giant that is generating energy fromcorehelium fusion.[5] A moderate level ofX-ray emission has been detected from this star,[13] which suggests it has a mildlyactive chromosphere.[5] The star is 650 million years old with more than double themass of the Sun, and has expanded to seven times theSun's radius. It is radiating 34 times theluminosity of the Sun from itsphotosphere at aneffective temperature of 5,071 K.[6]
TheWashington Double Star Catalogue lists a pair ofvisual companions for this star. Component B is magnitude 9.88 and lies at anangular separation of197.5 arcseconds along aposition angle (PA) of 162° from the brighter star as of 2003. Component C has a magnitude of 12.77 with a separation of129.3 arcseconds as of 2000.[14] Theproper motion of both stars are diverging significantly from 18 Delphini, so they can be ruled out as physical companions. However, a faint star located29.2″ away appears to be a co-moving companion. This has aprojected separation of2,199 AU and a mass estimated as 19% that of the Sun. It is a smallred dwarf star with a class of M4–5.[15]
On February 19, 2008, anextrasolar planet was found to be orbiting the star with a period of 2.720 years and a mild eccentricity (ovalness) of 0.08. The mass of this exoplanet is greater than 10 times themass of Jupiter.[5]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (Arion) | >10.3 MJ | 2.6 | 993.3 ± 3.2 | 0.08 ± 0.01 | — | — |
