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Fomalhaut (α PsA, α Piscis Austrini, Alpha Piscis Austrini) is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. Fomalhaut can be seen low in the southern sky in the northern hemisphere in fall and early winter evenings. Near latitude 50˚N, it sets around the time Sirius rises, and does not reappear until Antares sets. Its name means "mouth of the whale", from the Arabic فم الحوت fum al-ḥawt. It is a class A star on the main sequence approximately 25 light-years (7.7 pc) from Earth. It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk.

Fomalhaut holds a special significance in extrasolar planet research, as it is the center of the first stellar system with an extrasolar planet (Fomalhaut b) imaged at visible wavelengths. The image was published in Science in November 2008.[4]



Fomalhaut is believed to be a young star, only 100 to 300 million years old, with a potential lifespan of a billion years.[5][6] The surface temperature of the star is around 8,751 K (8,478 °C). Fomalhaut's mass is about 2.1 times that of the Sun, its luminosity is about 18 times greater, and its diameter is roughly 1.8 times as large.

Fomalhaut is metal-deficient as compared to the Sun, which means Fomalhaut is composed of a smaller percentage of elements other than hydrogen and helium.[1] The metallicity is typically determined by measuring the abundance of iron in the photosphere relative to the abundance of hydrogen. A 1997 spectroscopic study measured a value equal to 93% of the Sun's abundance of iron.[2][nb 1] A second 1997 study deduced a value of 78% by assuming Fomalhaut has the same metallicity as the neighboring star TW Piscis Austrini.[7] In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%.[1] Finally, in 2008, a spectroscopic measurement gave a significantly lower value of 46%.[3]

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