Astron. Astrophys. 348, 557-569 (1999)

6. Conclusion

We propose a two dust population model able to reproduce all the available observations of the HR 4796 A circumstellar disk. The first dust population, peaked at 70 AU from the star, shapes like a narrow annulus. Its small radial extension suggests a gravitational confinement mechanism both outside and inside the peak at 70 AU. This ring is made of amorphous grains quite similar to those found in the interstellar medium. Under the assumption of a collisionnal grain size distribution, grains larger than m to meter sized bodies are required to fit the data. Collisions, occurring in short time scales, are expected to produce smallest grains down to the blow out size limit (m). This conclusion applies because of the gas to dust ratio smaller than 1 inferred. The second dust population at 9-10 AU from the star is made of comet-like grains. Higher signal to noise ratio measurements and resolved images at m would allow to better constrain this dust population (spatial extension, grain size range) and its dynamics.

The dust surrounding HR 4796 A probably shows an intermediate stage for the circumstellar matter between pre-main sequence stars and evolved ones like Pictoris, Fomalhaut, Vega, 55 Cnc ... The presence of a companion (HR 4796 B) is also an interesting peculiarity among the Vega-like stars. As a large number of field stars are members of binary (or more) systems, HR 4796 A does not represent a marginal case. Therefore, the dynamics of the disk has to be further studied, in terms of chemical evolution of the grains and dust distribution to better understand the steps which lead or not to planetary systems formation.

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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