We have provided evidence that the planetary system of Cnc also hosts a Vega-like disk. The observations provide constraints to the disk structure which should comprise of not too large cometary dust particles at a distance of 50-60AU, i.e. about 4 arcsec, from the star. The presence of ice seems to be required to match the observations. The Pointing Robertson lifetime of the dust grains derived on the basis of the model shows that the dust grains in the disk must be replenished over the lifetime of the star, pointing to the existence of larger bodies, such as comets, from which the observed particles can be derived.
When the disks around main-sequence stars were first discovered, there was much speculation whether these disks were planetary systems in formation or, on the contrary, showed the failure of a system to produce planets. The age of some stars with excess made it obvious that this could not be due to on-going planet formation, but rather had to be a long-lasting phenomenon. There have been observational indications that Vega-like disks and planets might co-exist. Some Vega-like disks show indications of inner "voids" (Gillett 1986) with relatively lower dust densities. This has been attributed to the presence of planets (Diner and Appleby 1986). HST images of the Pic disk seem to indicate a small tilt of the inner disk which could be produced by a giant planet orbiting close to the inner edge of the disk in an inclined orbit (Burrows et al. 1995). Our own solar system has both planets and a dust disk (the zodiacal dust) which, however, would be undetectable from nearby stars with instruments like ISO or IRAS. The same is true for dust presumably associated with the Kuiper Belt (Backman et al. 1995).
The detection of a Vega-like excess associated with Cnc is the first evidence of both a planet and a disk around a star other than the Sun. We hope that this result will bring some clue to the discussion on formation and evolution of planetary systems.
© European Southern Observatory (ESO) 1998
Online publication: December 16, 1997