What stellar phenomenon causes the photocenter to shift, mimicking a planetary signal in astrometry?
Answer
Starspots, flares, or convective granules bubbling on the surface
A significant challenge in astrometry is noise originating from the host star itself, separate from the gravitational tug of the planet. Stellar phenomena, which include processes like starspots emerging, sudden flares occurring, or convective granules bubbling on the surface, can cause the visible center of light (the photocenter) to shift relative to the star's true gravitational center of mass. This surface variation creates a 'noise floor' that can mask or mimic the tiny, actual orbital wobble induced by a planetary companion, necessitating sophisticated modeling to separate the signals.
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