The fastest components in stellar jets
  Young stars accrete mass from a circumstellar disk, but at the same time disk
and star eject outflows and jets. These outflows have an onion-like structure
where the innermost and fastest layers are surrounded by increasingly lower
velocity components. The outer layers are probably photo-evaporative and
magnetocentrifugally launched disk winds, but the nature of the inner winds is
still uncertain. Since the fastest components carry only a small fraction of
the mass, they are best observed at high-energies (X-ray and UV) as the slower,
more massive components do not reach plasma temperatures sufficient for
relevant X-ray or UV emission. Outflows are the most likely way in which a star
or its disk can shed angular momentum and allow accretion to proceed; thus we
cannot understand the accretion and the rotation rate of young stars if we
cannot solve the origin of the inner jet components. Stellar jets share
characteristics with their counterparts in more massive astrophysical objects,
such as stellar mass black holes and AGN, with the added benefit that young
stars are found at much closer distances and thus scales not accessible in
other types of objects can be resolved. To understand the origin and impact of
the inner jets, sub-arcsecond imaging and spectroscopy in the UV and X-rays is
required, together with theory and modelling to interpret existing and future
observations.
