  Dust particles in orbit around a star drift toward the central star by the
Poynting-Robertson effect and pile up by sublimation. We analytically derive
the pile-up magnitude, adopting a simple model for optical cross sections. As a
result, we find that the sublimation temperature of drifting dust particles
plays the most important role in the pile-up rather than their optical property
does. Dust particles with high sublimation temperature form a significant dust
ring, which could be found in the vicinity of the sun through in-situ
spacecraft measurements. While the existence of such a ring in a debris disk
could not be identified in the spectral energy distribution (SED), the size of
a dust-free zone shapes the SED. Since we analytically obtain the location and
temperature of sublimation, these analytical formulae are useful to find such
sublimation evidences.
