Centroid Noise and Precision Astronomical Photometry

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Centroid noise is a random error, or "noise" component of a photometric measurement that results from placement of the measuring aperture on the object being measured. Centroid noise is not widely known as part of the internal error for a photometric measurement. In this Tech Note, I will examine the effect of centroid noise on stellar photometry. This study uses a series of repeated measurements of the same object to show the effect of centroid noise. The software used was Mira Pro, but the identical algorithms are used in Mira Pro x64. A photometric measurement involves measuring two quantities:

• The total signal is summed inside an aperture of a specified size, centered on the object.
• The background signal is estimated underneath the object. In aperture photometry, it is calculated using the pixels inside a ring (or annulus) concentric with the object.