Gamma Delphini

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Gamma Delphini
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Delphinus
Right ascension 20h 46m 38.7s
Declination +16° 7′ 38″
Apparent magnitude (V) 5.14 / 4.27
Spectral type F7V / K1IV
U−B color index 0.08 / 0.97
B−V color index 0.49 / 1.04
Variable type None
Radial velocity (Rv) −7 km/s
Proper motion (μ) RA: −25.88 mas/yr
Dec.: −196.27 mas/yr
Parallax (π) 32.14 ± 1.19 mas
Distance 101 ly
(31.1 pc)
Absolute magnitude (MV) 2.68 / 1.81
Mass 1.72/1.57[1] M
Radius 6.43/2.21[1] R
Luminosity 20.8/6.9 L
Temperature 4865/6303[1] K
Companion γ1 Del
Period (P) 3249 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) 2305
Argument of periastron (ω)
Other designations
12 Delphini, BD+15°4255, HD 197963/197964, HIP 102531/102532, HR 7947/7948, SAO 106475/106476, WDS 20467+1607
Database references

Gamma Delphini (γ Del, γ Delphini) is a binary star system approximately 101 light-years away in the constellation of Delphinus. The star marks one corner of the asterism "Job's Coffin". It is one of the best known double stars in the sky, with the primary star being a yellow-white dwarf star, while the secondary star is an orange subgiant star.

Stellar components[edit]

The primary star (catalogued as Gamma1 Delphini) is a yellow-white dwarf star of spectral type "F7V" and an apparent magnitude of 5.14. The star is thought to have about 7 times more luminosity than the Sun. The secondary star (Gamma2 Delphini) is an orange subgiant star of spectral type "K1IV" and an apparent magnitude of 4.27. This star is thought to have about 20.6 times more luminosity than the Sun. Nevertheless, the cooler component (Gamma2) is more massive than Gamma1 and according to the hierarchy of masses and brightness, Gamma2 should be the primary star of the system.

A planetary system?[edit]

Back in 1999 the presence of a planetary companion was inferred around Gamma2 Delphini, an evolved orange subgiant star.[1] Such a planet would yield 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).

So far 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.[3]

The Gamma Delphini planetary system[1]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (unconfirmed) ≥0.7 MJ 1.5 525.6  ?


  1. ^ a b c d e Irwin; et al. (1999). "A Program for the Analysis of Long-Period Binaries: The Case of γ Delphini". Precise Stellar Radial Velocities, ASP Conference Series#185, IAU Colloquium 170. Eds. J. B. Hearnshaw and C. D. Scarfe. Bibcode:1999ASPC..185..297I. 
  2. ^ 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. 
  3. ^ Wittemeyer; Endl, Michael; Cochran, William D.; Hatzes, Artie P.; Walker, G. A. H.; Yang, S. L. S.; Paulson, Diane B. (2006). "Detection Limits from the McDonald Observatory Planet Search Program". The Astronomical Journal. 132 (1): 177–188. arXiv:astro-ph/0604171Freely accessible. Bibcode:2006AJ....132..177W. doi:10.1086/504942. 

External links[edit]