  We study several realistic configurations allowing to realize an acoustic
horizon in the flow of a one dimensional Bose-Einstein condensate. In each case
we give an analytical description of the flow pattern, of the spectrum of
Hawking radiation and of the associated quantum fluctuations. Our calculations
confirm that the non local correlations of the density fluctuations previously
studied in a simplified model provide a clear signature of Hawking radiation
also in realistic configurations. In addition we explain by direct computation
how this non local signal relates to short range modifications of the density
correlations.
