Protostellar Outflows: a window to the past
  During the early phases of low-mass star formation, episodic accretion causes
the ejection of high-velocity outflow bullets, which carry a fossil record of
the driving protostar's accretion history. We present 44 SPH simulations of
$1\,\mathrm{M}_{\odot}$ cores, covering a wide range of initial conditions, and
follow the cores for five free-fall times. Individual protostars are
represented by sink particles, and the sink particles launch episodic outflows
using a subgrid model. The Optics algorithm is used to identify individual
episodic bullets within the outflows. The parameters of the overall outflow and
the individual bullets are then used to estimate the age and energetics of the
outflow, and the accretion events that triggered it; and to evaluate how
reliable these estimates are, if observational uncertainties and selection
effects (like inclination) are neglected. Of the commonly used methods for
estimating outflow ages, it appears that those based on the length and speed of
advance of the lobe are the most reliable in the early phases of evolution, and
those based on the width of the outflow cavity and the speed of advance are
most reliable during the later phases. We describe a new method that is almost
as accurate as these methods, and reliable throughout the evolution. In
addition we show how the accretion history of the protostar can be accurately
reconstructed from the dynamics of the bullets if each lobe contains at least
two bullets. The outflows entrain about ten times more mass than originally
ejected by the protostar.
