Photon noise estimation from the mean PSD in 8000-8200 μHz range over successive sub-series of 125 days with 15.625 days overlap. The top panel displays the photon noise of the GOLF instrument and the bottom panel, the ones from the mean corrected and not-corrected time series of green and red channels of VIRGO/SPMs. The grey zones in each panel indicate the period when SoHO was shut down due to the satellite recovery mission, and the red hatched area in the top panel highlights the dates of the red wing measurements from GOLF.