Tau Persei (τ Per), also known as 18 Persei, is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

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 ...

. The system is fairly close, and is located about 254

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 1012 ...

s (78 parsecs) away, based on its

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 objects ...

Tau Persei is an

eclipsing binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

, which means the two stellar components orbit each other in such an orientation that they periodically

eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...

each other, while blocking the other's light. Unlike many eclipsing binaries that have short

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

s, Tau Persei has an orbital period of 4.15 years. With a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of 0.055 arcseconds, this is one of the few eclipsing binaries whose components can be resolved with

interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

. The primary component of Tau Persei is a

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

with a spectral type of G8III. It has a radius 16 times that of the Sun, and is about 390 million years old. Its companion is an

A-type main-sequence star An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

. In 1989, the primary star eclipsed the secondary, allowing for the stellar parameters to be derived via its light curve.

Naming

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of va ...

, (), meaning ''

Mausoleum A mausoleum is an external free-standing building constructed as a monument enclosing the interment space or burial chamber of a deceased person or people. A mausoleum without the person's remains is called a cenotaph. A mausoleum may be consid ...

'', refers to an asterism consisting of τ Persei,

9 Persei 9 Persei is a single variable star in the northern constellation Perseus, located around 4,300 light years away from the Sun. It has the Bayer designation i Persei; ''9 Persei'' is the Flamsteed designation. This body is visible t ...

, ι Persei, κ Persei, β Persei, ρ Persei,

16 Persei 16 Persei is a single, suspected variable star in the northern constellation of Perseus (constellation), Perseus, located approximately 121 light years away based on parallax. It is visible to the naked eye as a yellow-white hued star wit ...

and

12 Persei 12 Persei (12 Per) is a double-lined spectroscopic binary star system in the northern constellation Perseus. Its combined apparent magnitude is 4.94, which means it can be viewed with the naked eye. Based upon parallax measurements, this ...

. Consequently, the Chinese name for τ Persei itself is (, en, the Second Star of Mausoleum.).AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 11 日
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References

{{DEFAULTSORT:Tau Persei Persei, Tau Perseus (constellation) G-type giants Persei, 18 Spectroscopic binaries 013531 017878 Durchmusterung objects 0854 A-type main-sequence stars Algol variables