  Narrow dust rings observed around some young stars (e.g., HR 4796A) need to
be confined. We present a possible explanation for the formation and
confinement of such rings in optically thin circumstellar disks, without
invoking shepherding planets. If an enhancement of dust grains (e.g., due to a
catastrophic collision) occurs somewhere in the disk, photoelectric emission
from the grains can heat the gas to temperatures well above that of the dust.
The gas orbits with super(sub)-Keplerian speeds inward (outward) of the
associated pressure maximum. This tends to concentrate the grains into a narrow
region. The rise in dust density leads to further heating and a stronger
concentration of grains. A narrow dust ring forms as a result of this
instability. We show that this mechanism not only operates around early-type
stars that have high UV fluxes, but also around stars with spectral types as
late as K. This implies that this process is generic and may have occurred
during the lifetime of each circumstellar disk. We examine the stringent
upper-limit on the H2 column density in the HR 4796A disk and find it to be
compatible with the presence of a significant amount of hydrogen gas in the
disk. We also compute the OI and CII infrared line fluxes expected from various
debris disks and show that these will be easily detectable by the upcoming
Herschel mission. Herschel will be instrumental in detecting and characterizing
gas in these disks.
