# Gamma Ceti

Observation data Characteristics Epoch J2000.0      Equinox J2000.0 Location of γ Ceti (circled) near the center Constellation Cetus Right ascension 02h 43m 18.03910s[1] Declination +03° 14′ 08.9390″[1] Apparent magnitude (V) 3.47[2] (3.56/6.63/10.16)[3] Spectral type A3 V + F3 V + K5[3] U−B color index +0.07[2] B−V color index +0.09[2] Radial velocity (Rv) –5.1[4] km/s Proper motion (μ) RA: –146.10[1] mas/yr Dec.: –146.12[1] mas/yr Parallax (π) 40.97 ± 0.63[1] mas Distance 80 ± 1 ly (24.4 ± 0.4 pc) Radius 1.9[5] R☉ Rotational velocity (v sin i) 186[6] km/s Age 300[7] Myr Gam Cet, 86 Ceti, BD+02 422, HD 16970, HIP 12706, HR 804, SAO 110707.[8]

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.[2] Based upon parallax measurements, this star is located at a distance of about 80 light years (24.4 parsecs) from Earth.[1]

## Properties

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.[3] 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.[9] 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.[3]

The measured angular diameter of the primary star is 0.74 ± 0.08 mas.[10] At the estimated distance of this system, this yields a physical size of about 1.9 times the radius of the Sun.[5] The secondary component of this system is an X-ray source with a luminosity of 2.2 × 1029 erg s–1.[11] Gamma Ceti is about 300[7] million years old and it appears to be a member of the stream of stars loosely associated with the Ursa Major moving group.[12] The primary has been examined for an excess of infrared emission that would suggest the presence of circumstellar matter, but none was found.[7]

## Etymology

The title Kaffaljidhma was derived from Arabic الكف الجذماء Al Kaff al Jidhmah, meaning "The cut-short hand".[13] 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).[14]

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.)[15]

## References

1. 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
2. ^ 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
3. ^ a b c d 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
4. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495.....
5. ^ a b 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:
\begin{align} 2\cdot R_* & = \frac{(24.4\cdot 0.74\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 3.88\cdot R_{\bigodot} \end{align}
6. ^ 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
7. ^ a b c 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
8. ^ "LTT 10892 -- High proper-motion Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-03-04
9. ^ 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
10. ^ Richichi; 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
11. ^ 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
12. ^ 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
13. ^ Allen, Richard Hinckley (1963), Star Names: Their Lore and Meaning (Dover ed.), University of Chicago, p. 160
14. ^ 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
15. ^