Zeta Cancri

Zeta Cancri (ζ Cancri, abbreviated Zeta Cnc, ζ Cnc) is a multiple star system in the constellation of Cancer. It is approximately 83.4 light-years from Earth, and has a combined apparent magnitude of +4.67. Since it is near the ecliptic, it can be occulted by the Moon and, very rarely, by planets.

The system is constituted as follows:
* A binary pair designated Zeta¹ Cancri or, alternatively, Zeta Cancri AB, the two components of which are themselves designated Zeta¹ Cancri A or, simply, Zeta Cancri A (formally also named Tegmine , the traditional name of the Zeta Cancri system) and Zeta¹/Zeta Cancri B.
* A triple star system designated Zeta² Cancri or alternatively Zeta Cancri C, consisting of a single star primary, designated Zeta²/Zeta Cancri Ca, together with a secondary binary pair, designated Zeta²/Zeta Cancri Cb. The binary pair's two components are themselves designated Zeta²/Zeta Cancri Cb1 and Cb2.

Nomenclature

''ζ Cancri'' ( Latinised to ''Zeta Cancri'') is the system's Bayer designation; ''ζ¹ Cancri'' and ''ζ² Cancri'' those of its two constituents. The designations of the two constituents as ''ζ Cancri AB'' and ''C'', and those of their components—''ζ Cancri A'', ''B'', ''Ca'', ''Cb'', ''Cb1'' and ''Cb2''—derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).

Considerable confusion had developed concerning the catalogue identities of the three bright stars; correct correspondences were worked out by Griffin:

''Zeta Cancri'' bore the traditional name ''Tegmine'' (''Tegmen'') "the shell (of the crab)". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Tegmine'' for the component ''Zeta¹ Cancri A'' on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.

In Chinese, (), meaning ''Water Level'', refers to an asterism consisting of Zeta Cancri, 6 Canis Minoris, 11 Canis Minoris and 8 Cancri. Consequently, Zeta Cancri itself is known as (, en, the Fourth Star of Water Level).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.

Properties

Zeta Cancri can be resolved as a binary star in small telescopes. Its binary nature was discovered in 1756 by Tobias Mayer. William Herschel resolved the two components that make up Zeta¹ Cancri in 1781. As early as 1831, John Herschel noticed perturbations in Zeta² Cancri's orbit around Zeta¹; this led Otto Wilhelm von Struve, in 1871, to postulate a fourth, unseen, component which orbited closely the visible member of Zeta². Later observations have resolved this fourth component and have indicated that there may be one or two more unobserved components.

Zeta¹ and Zeta² Cancri are 5.06 arcseconds apart. These two star systems orbit around their common centre of mass once every 1,100 years.

Zeta¹ Cancri

The two components are both yellow-white main-sequence dwarfs of spectral class F. The apparent magnitudes of A and B are +5.58 and +5.99, respectively. They are separated, as of 2008, by 1 arcsecond, requiring a large telescope to resolve them, but this separation will increase until the year 2020. They complete one orbit every 59.6 years. The estimated masses for the pair are 1.28 and 1.18 solar masses, respectively.

Zeta² Cancri

Zeta Cancri Ca is the brightest of the three components, 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 earlier, probably G0V. This star has around 1.15 solar masses. The tenth magnitude Zeta Cancri Cb is a close pair of red dwarfs. The separation between Ca and Cb is approximately 0.3 arcsecond, and their orbital period is 17 years.

References

{{Stars of Cancer

Cancer (constellation)
Cancri, Zeta
Cancri, 16
5
F-type main-sequence stars
G-type main-sequence stars
M-type main-sequence stars
Tegmine
Durchmusterung objects
040167
3208 09 10
068255 6 7