18 Delphini

18 Delphini, also named Musica /ˈmjuːzɪkə/,[8][9] is a single[10] star in the constellation of Delphinus of the low northern hemisphere. It has a Sun-like golden hue and is faintly visible to the naked eye with an apparent visual magnitude of 5.506.[2] The star is located at a distance of approximately 249 light years from the Sun based on parallax,[1] and it is drifting further away with a radial velocity of +4 km/s.[1] An object believed to be an extrasolar planet (designated 18 Delphini b or Arion) orbits the star.[5]

18 Delphini / Musica
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−V color 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]
Distance249 ± 2 ly
(76.4 ± 0.6 pc)
Absolute magnitude (MV)1.15[5]
Details[6]
Mass2.35±0.07 M☉
Radius7.19±0.38 R☉
Luminosity33.9+6.9
−5.7 L☉
Surface gravity (log g)3.00±0.04 cgs
Temperature5,071±10 K
Metallicity [Fe/H]0.10±0.02 dex
Rotational velocity (v sin i)1.60±0.45 km/s
Age690±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
SIMBADdata

Nomenclature

18 Delphini is the star's Flamsteed designation, abbreviated 18 Del. Following its discovery the planet was designated 18 Delphini b.[5]

As part of the NameExoWorlds program by the International Astronomical Union, in 2015 the name Musica, Latin for 'music', was selected for this star by Tokushima Prefectural Jonan High School Science Club of Japan. The planet was given the name Arion,[11] after 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. The constellation 'Delphinus' is Latin for 'dolphin'.[12][8]

Properties

The stellar classification of 18 Delphini is G6III,[3] which means it is an evolved star that has cooled and expanded off the main sequence. It is a suspected red clump giant that is generating energy from core helium fusion.[5] A moderate level of X-ray emission has been detected from this star,[13] which suggests it has a mildly active chromosphere.[5] The star is 650 million years old with more than double the mass of the Sun, and has expanded to seven times the Sun's radius. It is radiating 34 times the luminosity of the Sun from its photosphere at an effective temperature of 5,071 K.[6]

The Washington Double Star Catalogue lists a pair of visual companions for this star. Component B is magnitude 9.88 and lies at an angular separation of 197.5 arcseconds along a position angle (PA) of 162° from the brighter star as of 2003. Component C has a magnitude of 12.77 with a separation of 129.3 arcseconds as of 2000.[14] The proper motion of both stars are diverging significantly from 18 Delphini, so they can be ruled out as physical companions. However, a faint star located 29.2″ away appears to be a co-moving companion. This has a projected separation of 2,199 AU and a mass estimated as 19% that of the Sun. It is a small red dwarf star with a class of M4–5.[15]

Planetary system

On February 19, 2008, an extrasolar 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 the mass of Jupiter.[5]

The 18 Delphini planetary system[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 — —

References
  1. 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. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H.
  3. Opolski, A. (1957). "The spectrophotometric parallaxes of 42 visual binaries". Arkiv för Astronomi. 2: 55. Bibcode:1957ArA.....2...55O.
  4. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  5. Sato, Bun'ei; et al. (2008). "Planetary Companions around Three Intermediate-Mass G and K Giants: 18 Delphini, ξ Aquilae and HD 81688". Publications of the Astronomical Society of Japan. 60 (3): 539–550. arXiv:0802.2590. Bibcode:2008PASJ...60..539S. doi:10.1093/pasj/60.3.539. S2CID 18806627.
  6. Jofré, E.; et al. (2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets". Astronomy & Astrophysics. 574: A50. arXiv:1410.6422. Bibcode:2015A&A...574A..50J. doi:10.1051/0004-6361/201424474. S2CID 53666931.
  7. "HD 199665". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-10.
  8. "Naming Stars". iau.org. IAU. Retrieved 28 July 2016.
  9. "musica". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  10. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
  11. "Final Results of NameExoWorlds Public Vote Announced". IAU. Retrieved 2021-01-10.
  12. "Final Results of NameExoWorlds Public Vote Released". IAU. Retrieved 2021-01-10.
  13. Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009). "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources". The Astrophysical Journal Supplement. 184 (1): 138–151. arXiv:0910.3229. Bibcode:2009ApJS..184..138H. doi:10.1088/0067-0049/184/1/138. S2CID 119267456.
  14. Mason, B. D.; et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  15. Mugrauer, M.; et al. (March 2014). "New wide stellar companions of exoplanet host stars". Monthly Notices of the Royal Astronomical Society. 439 (1): 1063–1070. Bibcode:2014MNRAS.439.1063M. doi:10.1093/mnras/stu044.
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