The Period Window from previous section shows a dominant signal at 5.840 c/d. We will subtract this signal from the observations, leaving the so called residuals. We will then start a new period analysis on the residuals. This process is called prewhitening. If a dominant signal appears in the residuals, then the variable most likely is a multi-periodic system. 

  1. Select Prewhitening in the Period analysis menu or click on the Prewhitening button in the PerWin toolbar to display the Prewhitening  box. 

  2. Accept the default values and click OK to start the Prewhitening calculation using a frequency of 5.84040 c/d. This creates a new PerWin and you will notice the word *PREWHITENED* in the caption. We have removed the signal at 5.840 c/d, and now see a dominant period of 5.668 c/d. We now have good reasons to assume that V350 Peg is a multi-periodic Delta Scuti star with signals at 5.668 c/d and 5.840 c/d.