History of the solar-type protostar IRAS16293-2422 as told by the
  cyanopolyynes
  Cyanopolyynes are chains of carbon atoms with an atom of hydrogen and a CN
group on either side. They are detected almost everywhere in the ISM, as well
as in comets. In the past, they have been used to constrain the age of some
molecular clouds, since their abundance is predicted to be a strong function of
time. We present an extensive study of the cyanopolyynes distribution in the
solar-type protostar IRAS16293-2422 based on TIMASSS IRAM-30m observations. The
goals are (i) to obtain a census of the cyanopolyynes in this source and of
their isotopologues; (ii) to derive how their abundance varies across the
protostar envelope; and (iii) to obtain constraints on the history of
IRAS16293-2422. We detect several lines from HC3N and HC5N, and report the
first detection of DC3N, in a solar-type protostar. We found that the HC3N
abundance is roughly constant (~1.3x10^(-11)) in the outer cold envelope of
IRAS16293-2422, and it increases by about a factor 100 in the inner region
where Tdust>80K. The HC5N has an abundance similar to HC3N in the outer
envelope and about a factor of ten lower in the inner region. The HC3N
abundance derived in the inner region, and where the increase occurs, also
provide strong constraints on the time taken for the dust to warm up to 80K,
which has to be shorter than ~10^3-10^4yr. Finally, the cyanoacetylene
deuteration is about 50\% in the outer envelope and <5$\% in the warm inner
region. The relatively low deuteration in the warm region suggests that we are
witnessing a fossil of the HC3N abundantly formed in the tenuous phase of the
pre-collapse and then frozen into the grain mantles at a later phase. The
accurate analysis of the cyanopolyynes in IRAS16293-2422 unveils an important
part of its past story. It tells us that IRAS16293-2422 underwent a relatively
fast (<10^5yr) collapse and a very fast (<10^3-10^4yr) warming up of the cold
material to 80K.
