Neutron Stars in Binary Systems

Identifying the Parts of an X-ray Light Curve

Below is a sample of an X-ray light curve from an eclipsing X-ray binary such as HT Cas. See if you can correctly match the four labeled points in the light curve to the images below, showing what part of the orbit (as seen from Earth) that part of the light curve represents. The arrows show what direction the smaller (primary X-ray emitter) star is traveling.
lightcurve for one star passing behind another
  • Dotted lines or a darkened secondary star are behind the primary star

  • Solid lines or a white secondary star are in front of the primary star
smaller star crossing back
smaller star crossing front
smaller star going to back
smaller star coming to front

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