Epoch J2000.0 Equinox J2000.0
|Right ascension||02h 43m 18.03910s|
|Declination||+03° 14′ 08.9390″|
|Apparent magnitude (V)||3.47 (3.56/6.63/10.16)|
|Spectral type||A3 V + F3 V + K5|
|U−B color index||+0.07|
|B−V color index||+0.09|
|Radial velocity (Rv)||–5.1 km/s|
|Proper motion (μ)||RA: –146.10 mas/yr
Dec.: –146.12 mas/yr
|Parallax (π)||40.97 ± 0.63 mas|
|Distance||80 ± 1 ly
(24.4 ± 0.4 pc)
|γ Cet A|
|Rotational velocity (v sin i)||186 km/s|
Gamma Ceti (γ Cet, γ Ceti) is a star system in the equatorial constellation Cetus. It has the traditional name Kaffaljidhma and has an apparent visual magnitude of 3.47. Based upon parallax measurements, this star is located at a distance of about 80 light years (24.4 parsecs) from Earth.
Gamma Ceti appears to be a triple star system. The inner pair have an angular separation of 2.6 arcseconds. The primary component of this pair is a visual magnitude 3.6, A-type main sequence star with a stellar classification of A3 V. The fainter secondary component is an F-type main sequence star that has a classification of F3 V and a magnitude of 6.6. The contrasting colors of these two stars makes them a popular target of amateur astronomers. The two can be resolved with a small, 4 in (10 cm) aperture telescope under ideal seeing conditions, although at times they are can be a challenge to resolve even with a much larger scope. At a wide separation of 840 arcseconds is a dim, magnitude 10.2 K-type star with a classification of K5. The luminosity class of this last component remains undetermined.
The measured angular diameter of the primary star is 0.74 ± 0.08 mas. At the estimated distance of this system, this yields a physical size of about 1.9 times the radius of the Sun. The secondary component of this system is an X-ray source with a luminosity of 2.2 × 1029 erg s−1. Gamma Ceti is about 300 million years old and it appears to be a member of the stream of stars loosely associated with the Ursa Major moving group. The primary has been examined for an excess of infrared emission that would suggest the presence of circumstellar matter, but none was found.
The title Kaffaljidhma was derived from Arabic الكف الجذماء Al Kaff al Jidhmah, meaning "The cut-short hand". According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Kaff al Jidhmah was originally the title for five stars: γ Cet as Kaffaljidhma, ξ1 Cet as Al Kaff al Jidhmah I, ξ2 Cet as Al Kaff al Jidhmah II, δ Cet as Al Kaff al Jidhmah III and μ Cet as Al Kaff al Jidhmah IV (excluding α Cet and λ Cet).
In Chinese, 天囷 (Tiān Qūn), meaning Circular Celestial Granary, refers to an asterism consisting of γ Ceti, α Ceti, κ1 Ceti, λ Ceti, μ Ceti, ξ1 Ceti, ξ2 Ceti, ν Ceti, δ Ceti, 75 Ceti, 70 Ceti, 63 Ceti and 66 Ceti. Consequently, γ Ceti itself is known as 天囷八 (Tiān Qūn bā, English: the Eighth Star of Circular Celestial Granary.)
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- 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
- 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
- Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495.....
- Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
- Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224
- Su, K. Y. L. et al. (December 2006), "Debris Disk Evolution around A Stars", The Astrophysical Journal 653 (1): 675–689, arXiv:astro-ph/0608563, Bibcode:2006ApJ...653..675S, doi:10.1086/508649
- "LTT 10892 -- High proper-motion Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-03-04
- Mollise, Rod (2006), The urban astronomer's guide: a walking tour of the cosmos for city sky watchers, Patrick Moore's practical astronomy series, Springer, p. 200, ISBN 1-84628-216-0
- Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
- Schröder, C.; Schmitt, J. H. M. M. (November 2007), "X-ray emission from A-type stars", Astronomy and Astrophysics 475 (2): 677–684, Bibcode:2007A&A...475..677S, doi:10.1051/0004-6361:20077429
- King, Jeremy R.; Villarreal, Adam R.; Soderblom, David R.; Gulliver, Austin F.; Adelman, Saul J. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241
- Allen, Richard Hinckley (1963), Star Names: Their Lore and Meaning (Dover ed.), University of Chicago, p. 160
- Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 11 日
- Kaler, James B., "KAFFALJIDHMA (Gamma Ceti)", Stars (University of Illinois), retrieved 2012-03-04