PSD of HD 169392 data (grey) that was modelled as explained in the text (red curves) with the usual three components: white noise (W), granulation noise (B_g), and stellar activity and/or large scales of convection (B_a). The red continuous line is the sum of these three components, resulting from the fit of the smoothed spectrum over Δν (green line). The black curve corresponds to the spectrum smoothed over 101 bins, i.e. 12.8 μHz.