Gamma Delphini
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]
  | |
| 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[1] mas |
| Distance | 114.8 ± 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[2] mas |
| Distance | 114 ± 2 ly (35.1 ± 0.6 pc) |
| Absolute magnitude (MV) | 1.81[8] |
| Orbit[9] | |
| Companion | γ1 |
| 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 | |
| Mass | 1.61±0.04 M☉ |
| Radius | 2.60±0.12 R☉ |
| Luminosity | 10.2 L☉ |
| Surface gravity (log g) | 3.79±0.05 cgs |
| Temperature | 6,295±25 K |
| Metallicity [Fe/H] | 0.06±0.02 dex |
| Rotational velocity (v sin i) | 7.8[4] km/s |
| Age | 1.85±0.17 Gyr |
| γ2 | |
| Mass | 1.99±0.06 M☉ |
| Radius | 8.43±0.33 R☉ |
| Luminosity | 33.1 L☉ |
| Surface gravity (log g) | 3.04±0.06 cgs |
| Temperature | 4,798±20 K |
| Metallicity [Fe/H] | 0.12±0.03 dex |
| Rotational velocity (v sin i) | 3.6[10] km/s |
| Age | 1.81±0.11 Gyr |
| Other designations | |
| γ1: HD 197963, HIP 102531, HR 7947, SAO 106475 | |
| γ2: HD 197964, HIP 102532, HR 7947/7948, SAO 106476 | |
| Database references | |
| SIMBAD | γ Del |
| γ1 Del | |
| γ2 Del | |
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 the German astronomer F. G. W. Struve in 1755, and it has the discovery code STF 2727 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]
| 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
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
- 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.
- Kaler, James B., "Gamma Delphini", STARS, University of Illinois, retrieved 2017-03-29.
- 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
- 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.
- 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, p. 297, Bibcode:1999ASPC..185..297I, ISBN 1-58381-011-0
- 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.
- 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.
External links
- Ringwald, Frederick A. "Bright and Multiple Stars Gallery, taken at Fresno State's Campus Observatory, largely by students". California State University, Fresno. Retrieved 2008-07-02.
