We want to study the infrared emission from the circumstellar
  discs of young stars that are thought to be slightly older than
  the Herbig Ae/Be stars that still occur in star-forming regions,
  and younger than main-sequence stars, such as Beta Pictoris,
  for which faint circumstellar discs have been found by IRAS.
  Our main scientific goal is the study of the evolution of these
  circumstellar disks, an evolution which may be dominated by
  planet formation.  A hint for the formation of large bodies
  around our program stars is the conspicuous dip at 10 micron in
  the energy distributions of several of them.
  ISO will provide us with accurate energy distributions and with
  a variety of emission features from circumstellar dust grains.
  From these observations, we hope to obtain the geometrical extent
  and density distribution of the circumstellar grains as well as
  the grain size and chemical composition.  Comparison with data
  for younger and older objects will learn us how these parameters
  evolve with time.
  This proposal is an extension of a SWS central project.  It
  includes some recently identified objects as well as some hotter
  and thus more massive stars.