Zeta Cancri is a star system in the constellation Cancer containing at least four stars. It also has the traditional names Tegmine, Tegmen, or Tegmeni. It is approximately 83 light years from Earth, and has a combined apparent magnitude of +4.67. Since ζ Cancri is near the ecliptic, it can be occulted by the Moon and very rarely by planets.
Components
The ζ Cancri system contains two binary pairs, ζ1 Cancri and ζ2 Cancri, which are 5.06" apart. These two binary stars orbit around their common center of mass once every 1100 years. ζ Cancri can be resolved as a double star in small telescopes. Its double nature was discovered in 1756 by Johann Tobias Mayer. William Herschel resolved the two components that make up ζ1 Cancri in 1781. As early as 1831, John Herschel noticed perturbations in ζ2 Cancri's orbit around ζ1 Cancri. This lead Otto Wilhelm von Struve, in 1871, to postulate a fourth, unseen, component which closely orbited closely the visible component of ζ2 Cancri. Recent observations have resolved this fourth component, and have indicated that that there may be one or two more unobserved components.
The components of ζ1 Cancri are denoted ζ1 Cnc A and ζ1 Cnc B. They are both yellow-white main sequence stars of spectral class F. Their apparent magnitudes are +5.58 and +5.99, respectively. They complete one orbit every 59.3 years. As of 2005, they are separated by 0.8", requiring a large telescope to resolve; but their separation will increase until the year 2020.
The components of ζ2 Cancri are denoted ζ2 Cnc C and ζ2 Cnc D. ζ2 Cnc C is the brighter of the pair, having an apparent magnitude of +6.12. It appears to be a yellow G-type star, often reported as G5V, but now thought to be G0 V. The tenth-magnitude ζ2 Cnc D has the color of a red dwarf, and may in fact be a closely-orbiting pair of red dwarves. The separation between components C and D is approximately 0.3", and their orbital period is 17 years.
Considerable confusion has developed concerning the catalogue identities of the three bright stars. Correct correspondences are:
Component HR HD SAO HIP
ζ Cancri A 3208 68257 97645 40167 ζ Cancri B 3209 68256 97645 40167 ζ Cancri C 3210 68255 97646 40167