STEREO A observations of dust and its periodicity during an ISD focusing interval. (a) Daily dust count rate (blue) and median-smoothed count rate data (orange). (b) Indications of when STEREO A is moving in (red) or against (green) the interstellar flow direction. (c) Wavelet spectrogram of the daily dust count data from (a). (d) Wavelet power spectral values averaged over time, as a function of oscillation period. The three lines indicate averages over different time intervals: when STEREO A moves against the ISD flow (solid green), when it moves with the ISD flow (dashed red), and all time during the STEREO A focusing interval (dotted blue).