Impact on stellar population parameters of varying the [α/Fe] abundances of the SSP models used for the PPXF fit. The top panel shows the variation on the inferred (mass-weighted) metallicity, whereas the bottom panel shows the variation in the (mass-weighted) stellar age. Filled symbols refer to the fits performed with REGUL = 0, while empty symbols refer to the regularised fits. Different colours indicate the results for the three different objects, as highlighted by the legend.