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High-mass stars are rare, and since the early phases of star
formation
are short, protostellar precursors of high-mass stars are
only a few
in nearby giant molecular complexes. It is therefore
required to
observe, study and model massive protostars which are at
large distances
from the Sun and which are therefore usually not resolved as
individual
collapsing objects. In order to probe the properties
(luminosity, envelope
mass, spectral energy distribution, outflow power, etc ...)
of individual
collapsing objects as required to constrain the process of
formation, it is
thus essential to evaluate the effects of unresolved
clusters and multiple
systems on the quality of the obtained properties. Although
most works
on massive protostars are mentioning the problem of
unresolved clustering,
they usually do not account for it and most of the time a
real discussion
of the resulting biases is not given.
We will use some recent results from the Cygnus X project
(complete survey
for the earliest phases of high-mass stars in this
relatively nearby
massive complex) to illustrate the problem and to evaluate
the amplitude
of the over-estimations made by neglecting multiplicity and
of the
different level of clustering.
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