Zeta Cancri
Encyclopedia
Zeta Cancri is a star system
in the constellation
Cancer
containing at least four stars. It has the traditional name Tegmine (Tegmen) "the shell (of the crab)". The star system is approximately 83.4 light years from Earth
, and has a combined apparent magnitude
of +4.67.
In Chinese
, , meaning Water Level
, refers to an asterism consisting of ζ Cancri, 6 Canis Minoris
, 11 Canis Minoris
and 8 Cancri
. Consequently, ζ Cancri itself is known as
Since ζ Cancri is near the ecliptic
, it can be occulted
by the Moon
and, very rarely, by planet
s.
The ζ Cancri system contains two binary pairs, ζ¹ Cancri and ζ² Cancri, which are 5.06 arcseconds apart. These two binary stars orbit around their common centre of mass once every 1100 years.
ζ Cancri can be resolved as a double star in small telescopes. The double nature of ζ Cancri was discovered in 1756 by Johann Tobias Mayer
. It was discovered to be a triple star in 1781 by William Herschel
when he resolved the two components that make up ζ¹ Cancri. As early as 1831, John Herschel
noticed perturbations in ζ² Cancri's orbit around ζ¹ Cancri. This led Otto Wilhelm von Struve
, in 1871, to postulate a fourth, unseen, component which orbited closely the visible member of ζ² Cancri. Recent observations have resolved this fourth component and have indicated that there may be one or two more unobserved components.
The components of ζ¹ Cancri are denoted ζ Cancri A and ζ Cancri B. They are both yellow-white main sequence dwarfs
of spectral class
F. The apparent magnitude
the two stars are +5.58 and +5.99, respectively. The two stars 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 components of ζ² Cancri are denoted ζ Cancri C and ζ Cancri D. ζ Cancri 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 earlier, probably G0V. The tenth magnitude ζ Cancri D has the color of a red dwarf
, and may in fact be a close pair of two red dwarfs. The separation between C and D is approximately 0.3 arcseconds, and their orbital period is 17 years.
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Cancer
Cancer (constellation)
Cancer is one of the twelve constellations of the zodiac. Its name is Latin for crab and it is commonly represented as such. Its symbol is . Cancer is small and its stars are faint...
containing at least four stars. It has the traditional name Tegmine (Tegmen) "the shell (of the crab)". The star system is approximately 83.4 light years from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, and has a combined apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of +4.67.
In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
, , meaning Water Level
Well (Chinese constellation)
The Well mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the southern mansions of the Vermilion Bird.-Asterisms:...
, refers to an asterism consisting of ζ Cancri, 6 Canis Minoris
6 Canis Minoris
6 Canis Minoris is a star in the constellation Canis Minor.6 Canis Minoris is an orange K-type giant with an apparent magnitude of +4.55. It is approximately 560 light years from Earth....
, 11 Canis Minoris
11 Canis Minoris
11 Canis Minoris is a star in the constellation Canis Minor.11 Canis Minoris is a white A-type main sequence dwarf with an apparent magnitude of +5.25. It is approximately 312 light years from Earth....
and 8 Cancri
8 Cancri
8 Cancri is a star in the constellation Cancer.8 Cancri is a white A-type main sequence dwarf with an apparent magnitude of +5.14. It is approximately 211 light years from Earth....
. Consequently, ζ Cancri itself is known as
Since ζ Cancri is near the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
, it can be occulted
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
by the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
and, very rarely, by planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s.
The ζ Cancri system contains two binary pairs, ζ¹ Cancri and ζ² Cancri, which are 5.06 arcseconds apart. These two binary stars orbit around their common centre of mass once every 1100 years.
ζ Cancri can be resolved as a double star in small telescopes. The double nature of ζ Cancri was discovered in 1756 by Johann Tobias Mayer
Johann Tobias Mayer
Johann Tobias Mayer was a German physicist. He was mainly well known for his mathematics and natural science textbooks. Anfangsgründe der Naturlehre zum Behuf der Vorlesungen über die Experimental-Physik, an 1801 physics text, was the most influential of its time in the German-speaking countries...
. It was discovered to be a triple star in 1781 by William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
when he resolved the two components that make up ζ¹ Cancri. As early as 1831, John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
noticed perturbations in ζ² Cancri's orbit around ζ¹ Cancri. This led Otto Wilhelm von Struve
Otto Wilhelm von Struve
Otto Wilhelm von Struve was a Russian astronomer. In Russian, his name is normally given as Otto Vasil'evich Struve...
, in 1871, to postulate a fourth, unseen, component which orbited closely the visible member of ζ² Cancri. Recent observations have resolved this fourth component and have indicated that there may be one or two more unobserved components.
The components of ζ¹ Cancri are denoted ζ Cancri A and ζ Cancri B. They are both yellow-white main sequence dwarfs
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
of spectral class
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
F. The apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
the two stars are +5.58 and +5.99, respectively. The two stars 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 components of ζ² Cancri are denoted ζ Cancri C and ζ Cancri D. ζ Cancri C is the brighter of the pair, having an apparent magnitude of +6.12. It appears to be a yellow G-type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
star, often reported as G5V, but now thought to be earlier, probably G0V. The tenth magnitude ζ Cancri D has the color of a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
, and may in fact be a close pair of two red dwarfs. The separation between C and D is approximately 0.3 arcseconds, and their orbital period is 17 years.
Identification
Considerable confusion has developed concerning the catalogue identities of the three bright stars. Correct correspondences were worked out by Griffin:| Component | HR | HD Henry Draper Catalogue The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the... | SAO | HIP |
|---|---|---|---|---|
| ζ Cancri A | 3208 | 68257 | 97645 | 40167 |
| ζ Cancri B | 3209 | 68256 | ||
| ζ Cancri C | 3210 | 68255 | 97646 |