  The stellar reaction rates of radiative $\alpha$-capture reactions on heavy
isotopes are of crucial importance for the $\gamma$ process network
calculations. These rates are usually derived from statistical model
calculations, which need to be validated, but the experimental database is very
scarce. This paper presents the results of $\alpha$-induced reaction cross
section measurements on iridium isotopes carried out at first close to the
astrophysically relevant energy region. Thick target yields of
$^{191}$Ir($\alpha$,$\gamma$)$^{195}$Au, $^{191}$Ir($\alpha$,n)$^{194}$Au,
$^{193}$Ir($\alpha$,n)$^{196m}$Au, $^{193}$Ir($\alpha$,n)$^{196}$Au reactions
have been measured with the activation technique between E$_\alpha = 13.4$ MeV
and 17 MeV. For the first time the thick target yield was determined with X-ray
counting. This led to a previously unprecedented sensitivity. From the measured
thick target yields, reaction cross sections are derived and compared with
statistical model calculations. The recently suggested energy-dependent
modification of the $\alpha$+nucleus optical potential gives a good description
of the experimental data.
