Phi Andromedae (φ Andromedae, φ And) is the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

for a

binary star A binary star or binary star system 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 as separate stars us ...

system near the border of the northern

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 first constellati ...

of Andromeda. This system has a combined

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 4.25 and is visible to the naked eye. Based upon

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 made during the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

mission, this star system is located at a distance of about from Earth.

Nomenclature

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 China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...

, φ Andromedae forms the single-star asterism Jūnnánmén (軍南門 or 军南门, "Southern Millitary Gate"). R. H. Allen's ''

Star Names ''Star Names: Their Lore and Meaning'' is an 1899 book by Richard Hinckley Allen, that discusses the names of stars, constellations, and their histories. Background and authorship Richard Hinckley Allen (1838, near Buffalo, New York – 1908, ...

'' refers to this asterism as ''Keun Nan Mun'', "the Camp's South Gate", and includes

χ Andromedae Chi Andromedae ( Andromedae, And) is the Bayer designation for a star in the northern constellation of Andromeda. It has an apparent visual magnitude of +5.01, which is relatively faint for a naked-eye star. Based upon parallax measu ...

in it, but in Chinese sources χ Andromedae is a member of the Tian Dajiangjun (Heaven's Great General) asterism.AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日
Another identification of Jūnnánmén is α Trianguli.

Components

The 4.46 magnitude primary component is a

Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer ...

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 B7 Ve, indicating that it is a

B-type main sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

that shows prominent

emission lines A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

of hydrogen in its spectrum. These emission lines come from a flattened

decretion disk Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

of hot gas that is orbiting the host star. The star is rotating rapidly with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 75 km/s. The pole of the star is inclined around 20° to the line of sight from the Earth. The 6.06 magnitude companion star is a

with a classification of B9 V. On average the two stars are separated by about 0.6

arcsecond A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s and have an orbital period of roughly 554 years. Based upon their orbital elements, the system has a combined mass of around times the mass of the Sun.

References

External links

Image φ Andromedae

HR 0335

CCDM J01095+4715AB
{{DEFAULTSORT:Phi Andromedae Andromedae, Phi Andromeda (constellation) Binary stars B-type main-sequence stars B-type subgiants Emission-line stars Andromedae, 42 006811 005434 0335 BD+46 0275