The Binary Zoo

Observationally Based Classification

  1. Visual Binaries - the two stars are resolved and we can see them orbit each other.
    Example: Xi Boo

  2. Spectroscopic Binaries - spectral lines of one or both stars show Doppler shifts.
    Examples:Alpha Gem and Kappa Ari

  3. Astrometric Binaries - one star traces a sinusoidal path on the sky due to the influence of the unseen companion.
    Example: Sirius

  4. Eclipsing Binaries - the stars pass in front of each other as seen from Earth, causing the brightness to drop.
    Example: Algol

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