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Debris finder, PolCor-2
An instrument to detect debris around young stars


  1. Introduction
  2. Exoplanets
  3. Stars dust disc
  4. Albanova, research center in Stockholm
  5. The instrument, PolCor-2
  6. The mechanical box's surfaces
  7. Coronagraph
  8. Mirror set one
  9. Filters
  10. Lyot Stop
  11. Servo motors
  12. Polarizer
  13. Parabolic and flat mirror set two
  14. Lucky Imaging
  15. The camera
  16. The computer
  17. Test of the instrument that has been done
  18. Conclusion
  19. End of demonstration
  20. Follow up with links of information about coronagraphs

14: Lucky Imaging

If you want to study dust accumulations around other stars you study faint objects with very small angular spread. See the introductory image, the entire image field is only 1' (one arc minute, or 1/30 of the Moon diameter) and details of only fractions of the field. Total system resolution thus becomes a very important parameter. A major limiting factor is the atmosphere, the seing. NOT telescope located at a carefully selected spot, at 2400 meters hight at La Palma in the Atlantic Ocean, where there is very good properties in this regard.

But even so the atmosphere is changing constantly and cause bad seeing. If you can keep the exposure time very short, fractions of seconds you can be lucky and get a picture just when the atmosphere gives small contributory distortion. If you take a lot of pictures with short exposure you can get several sharp images. The technology is called the Lucky Imaging.

Now, this technology is excellent on our own planets around the Sun. They are very bright and one can therefore take short exposures, typical 1/100 second, and many images, shifting to align them exactly against each other and add them together (stacking). The dust emission around other stars, however, is very weak and noise arise when keep the exposure short. It can be compensated by adding together more than the usual 100 to 1000 exposures. However, it requires that the signal is significantly higher than the camera read-out noise, so unfortunately it is not the case for a standard camera under these circumstances.

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