γ Delphini
Location of γ Delphini (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Delphinus
γ1
Right ascension 20h 46m 38.86045s[1]
Declination +16° 07′ 26.8516″[1]
Apparent magnitude (V) 5.14
γ2
Right ascension 20+46
−39.49919[2]
Declination +16° 07′ 27.4358″[2]
Apparent magnitude (V) 4.360[3]
Characteristics
γ1
Spectral type F7V[4]
U−B color index 0.08
B−V color index 0.49
γ2
Evolutionary stage Subgiant[5]
Spectral type K1IV[6]
U−B color index 0.97
B−V color index 1.04
Astrometry
γ1
Radial velocity (Rv)−7.25±0.44[7] km/s
Proper motion (μ) RA: −11.153[1] mas/yr
Dec.: −203.341[1] mas/yr
Parallax (π)28.4068 ± 0.1504 mas[1]
Distance114.8 ± 0.6 ly
(35.2 ± 0.2 pc)
Absolute magnitude (MV)2.24[4]
γ2
Radial velocity (Rv)−6.33±0.35[7] km/s
Proper motion (μ) RA: −29.851[2] mas/yr
Dec.: −196.058[2] mas/yr
Parallax (π)28.5183 ± 0.4772 mas[2]
Distance114 ± 2 ly
(35.1 ± 0.6 pc)
Absolute magnitude (MV)1.81[8]
Orbit[9]
Companionγ1
Period (P)3,249 yr
Semi-major axis (a)10.22″
Eccentricity (e)0.88
Inclination (i)148.78°
Longitude of the node (Ω)88.06°
Periastron epoch (T)2,305
Argument of periastron (ω)
(secondary)		331.16°
Details[7]
γ1
Mass1.61±0.04 M☉
Radius2.60±0.12 R☉
Luminosity10.2 L☉
Surface gravity (log g)3.79±0.05 cgs
Temperature6,295±25 K
Metallicity [Fe/H]0.06±0.02 dex
Rotational velocity (v sin i)7.8[4] km/s
Age1.85±0.17 Gyr
γ2
Mass1.99±0.06 M☉
Radius8.43±0.33 R☉
Luminosity33.1 L☉
Surface gravity (log g)3.04±0.06 cgs
Temperature4,798±20 K
Metallicity [Fe/H]0.12±0.03 dex
Rotational velocity (v sin i)3.6[10] km/s
Age1.81±0.11 Gyr
Other designations
γ Del, 12 Delphini, BD+15°4255, CCDM J20467+1607, WDS 20467+1607
γ1: HD 197963, HIP 102531, HR 7947, SAO 106475
γ2: HD 197964, HIP 102532, HR 7947/7948, SAO 106476
Database references
SIMBADγ Del
γ1 Del
γ2 Del

Gamma Delphini, which is Latinized from γ Delphini, is a wide binary star system in the northern constellation of Delphinus. The star marks one corner of the asterism "Job's Coffin". The pair can be split with a modest amateur telescope and have been described as "one of the prettier pairs in the sky", with their contrasting colors said to be orange and lime in appearance.[11] Together, the system is visible to the naked eye with a combined apparent visual magnitude of 3.87.[12]

Space motion

The system is located at a distance of 115 light years from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −7 km/s. It is a member of the thin disk population,[7] and is a proposed member of the Wolf 630 moving group.[13]

This star was found to be a double by Christian Mayer and later observed by William Herschel on Sept 27th, 1779.[citation needed] It was later included as STF 2727 in the catalogue compiled by F. G. W. Struve and can be found under this name in the Washington Double Star Catalog. At the time, the components had an angular separation of 12.0″ along a position angle (PA) of 280°. As of 2019, they are separated by 8.90″ with a PA of 265°. The fainter component, designated γ1 Delphini, is of apparent magnitude 5.03. Its companion is a magnitude 4.360 star designated γ2 Delphini.[3] A fit of orbital elements to the available positional data provides a period of 3,249 years with a high eccentricity (ovalness) of 0.88.[9] Their physical separation ranges from roughly 40 out to 600 AU.[12]

Physical properties

The stellar classification of γ1 Delphini is F7V,[14] which matches an F-type main-sequence star with a yellow-white hue. It is about 1.8[7] billion years old and is spinning with a projected rotational velocity of 7.8 km/s.[4] The star has 1.6 times the mass and 2.6 times the radius of the Sun. It is radiating 10 times the Sun's luminosity from its photosphere at an effective temperature of 6,295 K.[7]

The brighter component, γ2 Delphini, has an orange hue with a class of K1IV.[6] Being the more massive star of the pair, it is the more evolved star and is currently on the subgiant branch.[5] It has double the mass of the Sun but has expanded to over eight times the Sun's radius. The star is radiating 33 times the luminosity of the Sun at 4,798 K.[7] It is spinning with a projected rotational velocity of 3.6 km/s.[10] The star displays a radial acceleration with a periodicity of 1.44 years, which may be the effect of an orbiting companion.[15]

The system is a source of X-ray emission with high probability.[16]

Possible planetary system

In 1999, the presence of a planetary companion was inferred around Gamma2 Delphini as one possible explanation for the radial velocity variations.[15] Such a planet would have a minimum mass of 0.7 Jupiter masses, orbital period of 1.44 years and separation of nearly 1.5 astronomical units (almost the orbital separation of Mars from the Sun). The planetary candidate has not been confirmed. McDonald Observatory researches have set mass limits for potential planetary companions in orbit around the star Gamma2 Delphini.[17]

The Gamma Delphini planetary system[15]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b (unconfirmed) ≥0.7 MJ 1.5 525.6 — — —

References

  1. ^ a b c d e f 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 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.
  3. ^ a b 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.
  4. ^ a b c d Luck, R. Earle (January 2017), "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants", The Astronomical Journal, 153 (1): 19, arXiv:1611.02897, Bibcode:2017AJ....153...21L, doi:10.3847/1538-3881/153/1/21, S2CID 119511744, 21.
  5. ^ a b Abt, Helmut A. (May 2019), "The Evolutionary Status of GK Subgiants", The Astronomical Journal, 157 (5): 5, Bibcode:2019AJ....157..177A, doi:10.3847/1538-3881/ab11c6, 177.
  6. ^ a b Cenarro, A. J.; et al. (2007), "Medium-resolution Isaac Newton Telescope Library of Empirical Spectra – II. The Stellar Atmospheric Parameters", Monthly Notices of the Royal Astronomical Society, 374 (2): 664–690, arXiv:astro-ph/0611618, Bibcode:2007MNRAS.374..664C, doi:10.1111/j.1365-2966.2006.11196.x, S2CID 119428437.
  7. ^ a b c d e f g Maldonado, J.; et al. (June 2013), "The metallicity signature of evolved stars with planets", Astronomy & Astrophysics, 554: 18, arXiv:1303.3418, Bibcode:2013A&A...554A..84M, doi:10.1051/0004-6361/201321082, S2CID 119289111, A84.
  8. ^ 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.
  9. ^ a b Hale, Alan (1994). "Orbital coplanarity in solar-type binary systems: Implications for planetary system formation and detection". The Astronomical Journal. 107 (1): 306–322. Bibcode:1994AJ....107..306H. doi:10.1086/116855.
  10. ^ a b Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
  11. ^ Consolmagno, Guy; Davis, Dan M. (2011), Turn Left at Orion: Hundreds of Night Sky Objects to See in a Home Telescope – and How to Find Them, Cambridge University Press, p. 128, ISBN 9781139503730.
  12. ^ a b Kaler, James B., "Gamma Delphini", STARS, University of Illinois, retrieved 2017-03-29.
  13. ^ Bubar, Eric J.; King, Jeremy R. (August 2010), "Spectroscopic Abundances and Membership in the Wolf 630 Moving Group", The Astronomical Journal, 140 (2): 293–318, arXiv:1005.1205, Bibcode:2010AJ....140..293B, doi:10.1088/0004-6256/140/2/293, S2CID 118455341
  14. ^ Deka-Szymankiewicz, B.; et al. (2018), "The Penn State - Toruń Centre for Astronomy Planet Search stars. IV. Dwarfs and the complete sample", Astronomy and Astrophysics, 615: A31, arXiv:1801.02899, Bibcode:2018A&A...615A..31D, doi:10.1051/0004-6361/201731696, S2CID 85526201.
  15. ^ a b c Irwin, A. W.; et al. (1999), Hearnshaw, J. B.; Scarfe, C. D. (eds.), "A Program for the Analysis of Long-Period Binaries: The Case of γ Delphini", Precise Stellar Radial Velocities. IAU Colloquium 170, ASP Conference Series #185, vol. 185, p. 297, Bibcode:1999ASPC..185..297I, ISBN 1-58381-011-0
  16. ^ 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.
  17. ^ Wittemeyer; et al. (2006). "Detection Limits from the McDonald Observatory Planet Search Program". The Astronomical Journal. 132 (1): 177–188. arXiv:astro-ph/0604171. Bibcode:2006AJ....132..177W. doi:10.1086/504942. S2CID 16755455.

External links

Constellation of Delphinus
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