ζ Cancri A/B/C
Location of ζ Cancri (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cancer
Right ascension 08h 12m 12.7s
Declination +17° 38′ 52″
Apparent magnitude (V) +5.58/+5.99/+6.12
Characteristics
Evolutionary stage main-sequence star
Spectral type F7V + F9V + G0V
Other designations
Tegmen, Tegmine, 16 Cancri, HR 3208/3209/3210, HD 68257/68255/68256, BD+18°1867, HIP 40167, SAO 97645/97646, GC 11142/11141, ADS 6650, CCDM J08123+1738, WDS 08122+1739

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:[1]

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).[3]

Considerable confusion had developed concerning the catalogue identities of the three bright stars; correct correspondences were worked out by Griffin:[4]

Component HR HD SAO HIP
ζ Cancri A 3208 68257 97645 40167
ζ Cancri B 3209 68255
ζ Cancri C 3210 68256 97646

Zeta Cancri bore the traditional name Tegmine (Tegmen) "the shell (of the crab)".[citation needed] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[5] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[6] 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.[2]

In Chinese, 水位 (Shuǐ Wèi), meaning Water Level, refers to an asterism consisting of Zeta Cancri, 6 Canis Minoris, 11 Canis Minoris and 8 Cancri.[7] Consequently, Zeta Cancri itself is known as 水位四 (Shuǐ Wèi sì, English: the Fourth Star of Water Level).[8]

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.[4] Later observations have resolved this fourth component and have indicated that there may be one or two more unobserved components.[9][10]

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.[11] 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.[12] 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

  1. ^ "Displaying next number in catalog HIP => 40167". Multiple Star Catalog. Archived from the original on 2018-02-18. Retrieved 2018-02-18.
  2. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  3. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  4. ^ a b Griffin, R. F. (2000). "Spectroscopic Binary Orbits from Photoelectrical Radial Velocities: Paper 150: ζ Cancri C". The Observatory. 120: 1–47. Bibcode:2000Obs...120....1G.
  5. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  6. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  7. ^ (in 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.
  8. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 19, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  9. ^ Hutchings, J. B.; Griffin, R. F.; Menard, F. (2000). "Direct observation of the fourth star in the Zeta Cancri system". Publications of the Astronomical Society of the Pacific (abstract). 112 (772): 833–836. arXiv:astro-ph/0004284. Bibcode:2000PASP..112..833H. doi:10.1086/316587. S2CID 119361568.
  10. ^ Richichi, A. (2000). "An Investigation of the multiple star Zet Cnc by a lunar occultation". Astronomy & Astrophysics. 364: 225–231. Bibcode:2000A&A...364..225R.
  11. ^ Mason; Hartkopf, William I.; Wycoff, Gary L.; Holdenried, Ellis R. (2006). "Speckle Interferometry at the US Naval Observatory. XII". The Astronomical Journal. 132 (5): 2219–2230. Bibcode:2006AJ....132.2219M. doi:10.1086/508231.
  12. ^ Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society, 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x
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