Phi Draconis (φ Dra / φ Draconis) is a fourth-magnitude

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

in the constellation

Draco Draco is the Latin word for serpent or dragon. Draco or Drako may also refer to: People * Draco (lawgiver) (from Greek: Δράκων; 7th century BC), the first lawgiver of ancient Athens, Greece, from whom the term ''draconian'' is derived * ...

. It has the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England. They are named for John Flamsteed who first used them while co ...

43 Draconis. It is also a

triple star 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 speak ...

system where the brightest component is a chemically peculiar

Ap star Ap and Bp stars are chemically peculiar stars (hence the "p") of spectral types A and B which show overabundances of some metals, such as strontium, chromium and europium. In addition, larger overabundances are often seen in praseodymium and neo ...

The brightness of φ Draconis varies by about 0.04 of a

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

every 1.7 days. This is due to very strong magnetic fields at the surface of the star, and it is classified as an α² Canum Venaticorum variable. φ Draconis is a multiple star system containing three stars. The inner pair form a single-lined spectroscopic binary in an eccentric 128-day orbit. The outermost star orbits the inner pair every 308 years. The outer pair can be resolved visually and have a semi-major axis of . A fourth component, C, is also listed in multiple star catalogues, but is only a chance alignment with the triple system. Phi Draconis Aa is a

main-sequence In astronomy, 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 He ...

Ap star with a spectral class of B8. The main abundance excess is silicon, although iron and chromium and also notably elevated. In

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the twe ...

, φ Draconis is called 柱史 (

Pinyin Hanyu Pinyin (), often shortened to just pinyin, is the official romanization system for Standard Chinese, Standard Mandarin Chinese in China, and to some extent, in Singapore and Malaysia. It is often used to teach Mandarin, normally writte ...

: Zhùshǐ), meaning ''Official of Royal Archives'', because this star is marking itself and stand alone in ''Official of Royal Archives'' asterism,

Purple Forbidden enclosure The Purple Forbidden enclosure ( Zǐ wēi yuán) is one of the San Yuan ( Sān yuán) or Three Enclosures. Stars and constellations of this group lie near the north celestial pole and are visible all year from temperate latitudes in the Northern ...

(see: Chinese constellations).AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日
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References

External links

*Jim Kaler's Stars, University of Illinois

*An Atlas of the Universe

{{Sky, 18, 20, 45.43, +, 71, 20, 16.13, 1000000 Draco (constellation) Ap stars Draconis, Phi Draconis, 43 170000 Zhùshǐ 柱史 089908 6920 Durchmusterung objects Alpha2 Canum Venaticorum variables B-type main-sequence stars Binary stars