Delta Geminorum
 Location of δ Geminorum (circled) |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Gemini |
| Right ascension | 07h 20m 07.37978s[1] |
| Declination | +21° 58′ 56.3377″[1] |
| Apparent magnitude (V) | +3.53[2] |
| Characteristics | |
| Spectral type | F0 IV[3] |
| U−B color index | +0.04[2] |
| B−V color index | +0.34[2] |
| Astrometry | |
| Radial velocity (Rv) | +4.1[4] km/s |
| Proper motion (μ) | RA: –15.13[1] mas/yr Dec.: –9.79[1] mas/yr |
| Parallax (π) | 53.94 ± 0.66[1] mas |
| Distance | 60.5 ± 0.7 ly (18.5 ± 0.2 pc) |
| Details | |
| Mass | 1.57[5] M☉ |
| Temperature | 6,900[6] K |
| Metallicity [Fe/H] | –0.26[6] dex |
| Rotational velocity (v sin i) | 129.7[7] km/s |
| Age | 1.6[6] Gyr |
| Other designations | |
Delta Geminorum (δ Gem, δ Geminorum) is a star in the constellation Gemini. It has the traditional name Wasat. The traditional name comes from the Arabic word for "middle". It has an apparent visual magnitude of +3.53,[2] allowing it to be seen with the naked eye. Wasat is only two-tenths of a degree south of the ecliptic, and therefore is occasionally occulted by the Moon and, more rarely, by a planet. The last occultation by a planet was by Saturn on June 30, 1857, and the next will be by Venus on August 12, 2420.[citation needed] In 1930, the dwarf planet Pluto was discovered about 0.5° to the east of this star by American astronomer Clyde Tombaugh.[8]
In Chinese, 天樽 (Tiān Zūn), meaning Celestial Wine Cup, refers to an asterism consisting of δ Geminorum, 57 Geminorum and ω Geminorum.[9] Consequently, δ Geminorum itself is known as 天樽二 (Tiān Zūn èr, English: the Second Star of Celestial Wine Cup.)[10]. From this Chinese name, the name Ta Tsun was appeared.[11]
[edit] Properties
Delta Geminorum is a subgiant star with the stellar classification F0 IV.[3] It is about 60.5 light-years (18.5 parsecs) distant.[1] This star has 1.57 times the mass of the Sun[5] and is rotating rapidly with a projected rotational velocity of 129.7 km s–1.[7] The estimated age is 1.6 billion years.[6]
Wasat is a member of a triple star system. The inner components form a spectroscopic binary with a period of 6.1 years (2,238.7 days) and an orbital eccentricity of 0.3530. A cooler class K companion is not apparent to the naked eye but clearly visible in a small telescope. It orbits the inner pair with a period of 1,200 years and an eccentricity of 0.11.[12][13] Although its radial velocity is away from the Sun, this system is following a transverse trajectory that will bring it closer to the Solar System. In about 1.1 million years, it will make its closest approach at a separation of roughly 6.7 ly (2.1 pc).[14]
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c d Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode 1966CoLPL...4...99J
- ^ a b c "Delta Geminorum (Wasat)", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Delta+Geminorum, retrieved 2011-06-03
- ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, ed., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, http://adsabs.harvard.edu/abs/1967IAUS...30...57E, retrieved 2009-09-10
- ^ a b Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", The Astrophysical Journal Supplement 192 (1): 2, Bibcode 2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2
- ^ a b c d Nordström, B. et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics 418: 989–1019, arXiv:astro-ph/0405198, Bibcode 2004A&A...418..989N, doi:10.1051/0004-6361:20035959
- ^ a b Schröder, C.; Reiners, J. H. M. M.; Schmitt (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics 493 (3): 1099–1107, Bibcode 2009A&A...493.1099S, doi:10.1051/0004-6361:200810377
- ^ O'Meara, Stephen James (2002), The Caldwell objects, Deep-sky companions, Cambridge University Press, p. 156, ISBN 0521827965, http://books.google.com/books?id=3Hg6YHgx9nAC&pg=PA156
- ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Gemini
- ^ Abt, Helmut A. (August 2005), "Observed Orbital Eccentricities", The Astrophysical Journal 629 (1): 507–511, Bibcode 2005ApJ...629..507A, doi:10.1086/431207
- ^ Kaler, James B., "WASAT (Delta Geminorum)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/wasat.html, retrieved 2012-01-30
- ^ García-Sánchez, J. et al. (November 2001), "Stellar encounters with the solar system", Astronomy and Astrophysics 379: 634–659, Bibcode 2001A&A...379..634G, doi:10.1051/0004-6361:20011330
[edit] External links
- Delta Geminorum on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
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