Epsilon Persei, Latinized from ε Persei, is a multiple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speakin ...

in the northern constellation of

Perseus In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...

. It has a combined apparent visual magnitude of +2.88, which is bright enough to be viewed with the naked eye. Based upon

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...

measurements, this system is located at a distance of roughly 640

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...

s (196

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, a ...

s) from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

. This is a spectroscopic binary system, which means that the presence of an orbiting companion has been revealed by

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

variations in the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of color ...

of the primary. The two components are orbiting each other with a period of 14 days at a high

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values b ...

of 0.55. The secondary component has about 6–13% of the primary's mass and may have a

stellar classification 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 t ...

in the range from A6 V to K1 V. There may be a third component to this system with an orbital period of roughly 9,428 days (25.8 years), although this has not been conclusively demonstrated. If this component exists, it would have about 51–139% of the primary's mass. This high level of uncertainty is because the

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of the orbit is not known. EpsilonPerLightCurve

The primary component of this system, Epsilon Persei A, is a massive star with 12–16 times the

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

and near eight times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.9 ...

. It has a stellar classification of B0.5 V, making it a B-type main sequence star that is generating energy at its core through the

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifest ...

of hydrogen. Component A is radiating over 28,000 times the

Sun's luminosity The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nomi ...

from its outer envelope 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 26,500 K. This gives the star the blue-white hue that is typical of B-type stars. Epsilon Persei A is a Beta Cephei variable star with a primary pulsation period of 0.1603 days, or 6.24 cycles per day. It may have multiple pulsation frequencies.

References

External links

Al-Thurayya

{{Stars of Perseus B-type main-sequence stars Beta Cephei variables Alpha Persei Cluster Perseus (constellation) Persei, Epsilon Durchmusterung objects Persei, 45 024760 018532

1220 Year 1220 ( MCCXX) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. Events By place Fifth Crusade * July – The Crusaders, led by the Knights Hospitaller, raid Burlus, located i ...

Spectroscopic binaries