Eta Cephei (η Cep, η Cephei) is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the northern

circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest p ...

of Cepheus. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 3.4, this is a third magnitude star that, according to the

Bortle Dark-Sky Scale The Bortle dark-sky scale (usually referred to as simply the Bortle scale) is a nine-level numeric scale that measures the night sky's sky brightness, brightness of a particular location. It quantifies the astronomy, astronomical observability of ...

, is readily visible to the naked eye.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements put it at a distance of from Earth.

Etymology

Eta Cephei, along with α Cephei (Alderamin) and β Cep (Alfirk), were identified as ''Al Kawākib al Firḳ'' (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg. Together with θ Cephei, it form ''Al Kidr''. Among its other designations includes the name ''Kabalfird''. In Chinese, (), meaning '' Celestial Hook'', refers to an asterism consisting of η Cephei, 4 Cephei, HD 194298, θ Cephei, α Cephei,

ξ Cephei Xi Cephei (ξ Cephei, abbreviated Xi Cep, ξ Cep) is a multiple star system in the constellation of Cepheus. It is approximately 102 light-years from Earth and has an apparent magnitude for all the components combined of 4.29. It consi ...

, 26 Cephei, ι Cephei and ο Cephei. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for η Cephei itself is (, .).
AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 6 日

Properties

Eta Cephei is a

subgiant star A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of K0 IV, which indicates it is exhausting the supply of hydrogen at its core and is in the process of

evolving Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...

into a

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

. With 1.4 times the

Sun's mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

, at an age of 2.5 billion years it has reached a radius 3.86 times larger than the Sun and a luminosity eight times greater. It is radiating this energy from its outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 5,000 K, giving it the orange-hued glow of a

K-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

. Eta Cephei has a high

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

across the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

and a large

peculiar velocity Peculiar motion or peculiar velocity refers to the velocity of an object relative to a ''rest frame''—usually a frame in which the average velocity of some objects is zero. Galactic astronomy In galactic astronomy, peculiar motion refers to t ...

of .

Hunt for substellar objects

According to Nelson & Angel (1998), Eta Cephei would show two significant periodicities of 164 days and 10 years respectively, hinting at the possible presence of one or more jovian planets in orbit around the subgiant. The authors have set an upper limit of 0.64

Jupiter masses The Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter i ...

for the putative inner planet and 1.2

for the putative outer one. Also Campbell et al. (1988) inferred the existence of planetary objects or even

brown dwarfs Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter ()not big enough to sustain nuclear fu ...

less massive than 16.3

. However, more recent studies have not yet confirmed the existence of any substellar companion around Eta Cephei.

McDonald Observatory McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional faci ...

team has set limits to the presence of one or more planets with masses between 0.13 and 2.4

and average separations spanning between 0.05 and 5.2 AU.

References

{{DEFAULTSORT:Eta Cephei Cephei, Eta Cepheus (constellation) Hypothetical planetary systems K-type subgiants Cephei, Eta Cephei, 03 102422 198149 Durchmusterung objects 7957