page_title: Epsilon Aurigae
section_title: Visible component
hierarchical_section_title: Epsilon Aurigae / Nature of the system / Visible component
caption_attribution_description: English: This is an artistic rendering of the epsilon Aurigae star system.
context_page_description: Epsilon Aurigae is a multiple star system in the northern constellation of Auriga. It is an unusual eclipsing binary system comprising an F0 supergiant and a companion which is generally accepted to be a huge dark disk orbiting an unknown object, possibly a binary system of two small B-type stars. The distance to the system is still a subject of debate, but data from the Gaia spacecraft puts its distance at around 1,350±300 light years from Earth.
  Epsilon Aurigae was first suspected to be a variable star when German astronomer Johann Heinrich Fritsch observed it in 1821. Later observations by Eduard Heis and Friedrich Wilhelm Argelander reinforced Fritsch's initial suspicions and attracted attention to the star. Hans Ludendorff, however, was the first to study it in great detail. His work revealed that the system was an eclipsing binary variable, a star that dims when its partner obscures its light.
  About every 27 years, Epsilon Aurigae's brightness drops from an apparent visual magnitude of +2.92 to +3.83. This dimming lasts 640–730 days. In addition to this eclipse, the system also has a low amplitude pulsation with a non-consistent period of around 66 days.
context_section_description: The visible component, Epsilon Aurigae A, is a semiregular pulsating post-asymptotic giant branch star belonging to the spectral class F0. This F-type star has around 143 to 358 times the diameter of the Sun, and is 37,875 times as luminous. (Reliable sources vary considerably in their estimates of both quantities.) If the star were in the position of the Sun, it would envelop Mercury and possibly Venus. F-type stars like Epsilon Aurigae tend to glow white and display strong ionized calcium absorption lines and weak hydrogen absorption lines; being a class above the Sun (which is a G-type star), F-type stars are typically hotter than sunlike stars. Other F-type stars include Procyon's primary star, the brightest star in the constellation Canis Minor.
  The supergiant pulsates, showing small variations in its brightness and spectral lines.  The pulsations have been given periods of 67 and 123 days, with an amplitude of about 0.05 magnitudes.  The profiles of many spectral lines show variations that would be expected from a pulsating spergiant, but it isn't clear if they have the same period as the brightness variations.  There may be a small variation in the effective temperature of the photosphere as the star pulsates.
caption: The ε Aurigae system during an eclipse (artist impression)
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