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A-type main-sequence star

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An artists impression of Sirius A. Sirius A is a A-type main-sequence star.

An A-type main-sequence star (A V), also known as A dwarf star, is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V. They have masses from 1.4 to 2.1 times the mass of the Sun, and surface temperatures anywhere from 7600 K (7326 °C, 13220 °F) to 10000 K (9726 °C, 17540 °F). Very bright and nearby examples of A-type main-sequence stars are Altair (A7V), Sirius A (A1V), and Vega (A0V)


Class A stars are young (typically only a few hundred million years old), and many emit infrared radiation beyond what would be expected from the star alone. This IR excess is attributable to dust emission from a debris disk where planets form. Massive planets, usually Super Jupiters and Hot Jupiters, commonly form around class A stars though these planets are difficult to detect with the Doppler spectroscopy method. This is because class A stars rotate very quickly, this makes it difficult to measure small Doppler shifts induced by orbiting planets since the spectral lines are very broad. However, this type of star eventually evolves into a cooler red giant which rotates more slowly, and thus can be measured using the radial velocity method. A planet has also been found orbiting a Class A star. The planet is Fomalhaut b. Also, as of early 2011, about 30 Jupiter class planets have been found around evolved K-giant stars, including Pollux, Gamma Cephei, and Iota Draconis.

A-type main-sequence star characteristicsEdit


  • Mass: 2.40 Solar mass
  • Radius: 1.87 Solar radius
  • Absolute magnitude: 0.7
  • Temperature: 9727 K (9453 °C, 17048 °F)


  • Mass: 2.19 Solar mass
  • Radius: 1.78 Solar radius
  • Absolute magnitude: 1.3
  • Temperature: 8820 K (8546 °C, 15416 °F)


  • Mass: 1.86 Solar mass
  • Radius: 1.69 Solar radius
  • Absolute magnitude: 2.0
  • Temperature: 7880 K (7606 °C, 13724 °F)


  • Mass: 1.80 Solar mass
  • Radius: 1.66 Solar radius
  • Absolute magnitude: 2.1
  • Temperature: 7672 K (7398 °C, 13349 °F)


  • Mass: 1.74 Solar mass
  • Radius: 1.63 Solar radius
  • Absolute magnitude: 2.3
  • Temperature: 7483 K (7209 °C, 13009 °F)


  • Mass: 1.62 Solar mass
  • Radius: 1.55 Solar radius
  • Absolute magnitude: 2.5
  • Temperature: 7112 K (6838 °C, 12341 °F)

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