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Hubble Space Telescope
Aperture Photometry

A common method of data analysis involves simply adding up the counts within some circular aperture.

The signal-to-noise ratio will depend on the aperture size used. An aperture which is either very small or very large compared to the PSF will result in low signal-to-noise ratio.

The aperture radius can be specified in pixels, where one PC pixel is 0.0455 arcseconds, and one WFC pixel is 0.0996 arcseconds.

John Biretta <biretta@stsci.edu>, STScI