Stellar variability that contaminates a planetary radial-velocity or photometric signal. Rotating active regions, changes in convective line shifts, oscillations and granulation can produce apparent velocities. A common spectral shift, line-shape diagnostics, activity indicators and simultaneous photometry provide different tests; none is an automatic numerical probability.
The midpoint of the two wings of a stellar absorption line at each depth. A changing line bisector can reveal profile distortions caused by active regions or blends rather than a rigid Doppler shift of the whole spectrum.
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