SIMBAD references

Debris rings of dust are found around young luminous stars such as HR 4796A and HD 141569. Some of these entities have sharp edges and gaps, which have been interpreted as evidence for the presence of shepherding and embedded planets. Here we show that gaps and sharp edges in the debris disks of dust can also be spontaneously self-generated if they are embedded in optically thin regions of gaseous disks. This clumping instability arises in regions where an enhancement in the dust density leads to local gas temperature and pressure increases. Consequently, the relative motion between the gas and the dust is modified. The subsequent hydrodynamic drag on the dust particles leads to further enhancement of their concentration. We show that this process is linearly unstable and leads to the formation of ringlike structures within the estimated lifetime of such young objects. Once the gas is removed (e.g., by photoevaporation), the structures are ``frozen'' and will persist, even when the gas might not be observable anymore.