Binary Star Systems (AQA A Level Physics)

• The Doppler effect can be used to identify eclipsing binary star systems
• An eclipsing binary star system is

Where two stars orbit around a common centre of mass with their orbital plane in the Earth's line of sight

• This means that, when observed from Earth, the stars cross in front of each other as they orbit, appearing to periodically eclipse one another
• They can be identified from their characteristic light curves

Light Curve of an Eclipsing Binary

The light intensity curve of an eclipsing binary shows periodic dips of two different sizes

• The primary minima (the larger dips) are caused by the cooler star passing in front of the hotter star 
  • When the hotter star is eclipsed, more light is blocked which results in deeper minima

• The secondary minima (the smaller dips) are caused by the hotter star passing in front of the cooler star
  • When the cooler star is eclipsed, less light is blocked which results in shallower minima