Do siblings always form and evolve simultaneously? Testing the coevality
  of multiple protostellar systems through SEDs
  Multiplicity is common in field stars and among protostellar systems. Models
suggest two paths of formation: turbulent fragmentation and protostellar disk
fragmentation. We attempt to find whether or not the coevality frequency of
multiple protostellar systems can help to better understand their formation
mechanism. The coevality frequency is determined by constraining the relative
evolutionary stages of the components in a multiple system. SEDs for known
multiple protostars in Perseus were constructed from literature data. Herschel
PACS photometric maps were used to sample the peak of the SED for systems with
separations >7", a crucial aspect in determining the evolutionary stage of a
protostellar system. Inclination effects and the surrounding envelope and
outflows were considered to decouple source geometry from evolution. This
together with the shape and derived properties from the SED was used to
determine each system's coevality as accurately as possible. SED models were
used to examine the frequency of non-coevality that is due to geometry. We find
a non-coevality frequency of 33+/-10% from the comparison of SED shapes of
resolved multiple systems. Other source parameters suggest a somewhat lower
frequency of non-coevality. The frequency of apparent non-coevality that is due
to random inclination angle pairings of model SEDs is 17+/-0.5%. Observations
of the outflow of resolved multiple systems do not suggest significant
misalignments within multiple systems. Effects of unresolved multiples on the
SED shape are also investigated. We find that 1/3 of the multiple protostellar
systems sampled here are non-coeval, which is more than expected from random
geometric orientations. The other 2/3 are found to be coeval. Higher order
multiples show a tendency to be non-coeval. The frequency of non-coevality
found here is most likely due to formation and enhanced by dynamical evolution.
