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The gravitational perturbations between a circumstellar disk and a planet are the same as the perturbations created in a planetary ring by one or more satellites.

Modelling the structures observed in circumstellar disks allows us to work back to the characteristics of the planets that cause these structures. For example, the principal mechanism capable of generating asymmetrical brightness in a disk of dust is trapping in resonance with a planet. This mechanism has been advanced to explain the asymmetries seen in the extrasolar disks such as P Pictoris or Vega (Fig. 6.17). In the Solar System, dust has been detected, trapped in resonance with the Earth by the same mechanism.

The disk of P Pictoris (Sect. 6.3) has been better studied than any other debris disk. It shows other signs of the presence of one or more planets, in addition to the absorptions in the star's spectrum just mentioned. A short decline in the flux from the star has been interpreted as an eclipse by a planet. The disk shows a vertical asymmetry (a butterfly-like effect), which also betrays the presence of a planet in an inclined orbit.

RA offset, AU RA offset, arcsec

Fig. 6.17 Numerical models of dust trapped in resonance with a planet (left) and comparison with Vega's disk (right). The square indicates the position of the planet (Wyatt, 2003)

RA offset, AU RA offset, arcsec

Fig. 6.17 Numerical models of dust trapped in resonance with a planet (left) and comparison with Vega's disk (right). The square indicates the position of the planet (Wyatt, 2003)

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Chapter 7

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