Distance of a planet to the star?
Use this (http://www.ast.cam.ac.uk/~mjp/calc_parallax.html) but substitute the exoplanet for the Earth, you don't need to involve the Sun in your calculations, just assume the star is 3pc (parsecs) from Earth.




  From Figure 2, the distance between the Sun and the star is : 
  d = r / tan P 
  If P is 1 second of arc: 
  d = 150 000 000 / tan 1" = 30 million million km 
  This distance is called one parsec and is a basic unit for measuring astronomical distances. 
  Distance in parsecs = 1 / P in seconds of arc