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Atypemainsequence

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 of around 1.4 to 2.1 times the mass of the Sun, and surface temperatures anywhere from 7112 K (6838 °C; 12341 °F) to 11500 K (11226 °C; 20240 °F). Very bright and nearby examples of A-type main-sequence stars are Altair (A7 V), Sirius A (A1 V), and Vega (A0 V)

PlanetsEdit

A-type stars are young, typically around a few hundred million years, 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. Surveys indicate massive planets commonly form around A-type stars although these planets are difficult to detect using the Doppler spectroscopy method. This is because A-type stars typically rotate very quickly, which makes it very difficult to measure the small Doppler shifts induced by orbiting planets since the spectral lines are very broad. However, this type of massive star eventually evolves into a cooler red giant which rotates more slowly and thus can be measured using the radial velocity method. As of early 2011 about 30 Jupiter class planets have been found around evolved K-giant stars including Pollux, Gamma Cephei and Iota Draconis. Doppler surveys around a wide variety of stars indicate about 1 in 6 stars having twice the mass of the Sun are orbited by one or more Jupiter-sized planets, vs. 1 in 16 for Sun-like stars.

A-type stars known to have planets include Fomalhaut, HD 15082, Beta Pictoris and HD 95086.

A-type main-sequence star characteristicsEdit

A0 VEdit

  • Mass: 2.40 Solar mass
  • Radius: 1.87 Solar radius
  • Absolute magnitude: 0.7
  • Temperature: 11500 K (11226 °C; 20240 °F)

A2 VEdit

  • Mass: 2.19 Solar mass
  • Radius: 1.78 Solar radius
  • Absolute magnitude: 1.3
  • Temperature: 10530 K (10256 °C; 18494 °F)

A5 VEdit

  • Mass: 1.86 Solar mass
  • Radius: 1.69 Solar radius
  • Absolute magnitude: 2.0
  • Temperature: 8200 K (7926 °C; 14300 °F)

A6 VEdit

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

A7 VEdit

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

A8 VEdit

  • Mass: 1.66 Solar mass
  • Radius: 1.60 Solar radius
  • Absolute magnitude: 2.4
  • Temperature: 7305 K (7031 °C; 12689 °F)

A9 VEdit

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