  Irradiation effects in close binaries are crucial for a reliable
determination of system parameters and understanding the close binary
evolution. We study irradiated light originating from the low mass component of
an eclipsing system comprising a hot subdwarf primary and a low mass companion,
to precisely interpret their high precision photometric and spectroscopic data,
and accurately determine their system and surface parameters. We re-analyse the
archival VLT/UVES spectra of AA Dor system where irradiation features have
already been detected. After removing the predominant contribution of the hot
subdwarf primary, the residual spectra reveal more than 100 emission lines from
the heated side of the secondary with maximum intensity close to the phases
around secondary eclipse. We analyse 22 narrow emission lines of the irradiated
secondary, mainly of OII, with a few CII lines. Their phase profiles constrain
the emission region of the heated side to a radius $\geq$ 95% of the radius of
the secondary. The shape of their velocity profiles reveals two distinct
asymmetry features one at the quadrature and the other at the secondary
eclipse. We identify more than 70 weaker emission lines originating from HeI,
NII, SiIII, CaII and MgII. We correct the radial velocity semi-amplitude of the
center-of-light to the centre-of-mass of the secondary and calculate accurate
masses of both components. The resulting masses $M_{1}$=0.46 $\pm$
0.01$M_{\odot}$ and $M_{2}$=0.079 $\pm$ 0.002$M_{\odot}$ are in perfect
accordance with those of a canonical hot subdwarf primary and a low mass star
just at the substellar limit for the companion. We compute a first generation
atmosphere model of the irradiated low mass secondary, which matches the
observed spectrum well. We find an indication of an extended atmosphere of the
irradiated secondary star.
