Photometry with a periodic grid. I. A new method to derive angular diameters and brightness distribution.

Abstract

The interest of observations of point sources with a periodic grid has been recognized for long in astrometry because of the direct relation existing between the position in the sky and the phase of the modulated signal. We investigate in this paper a complementary aspect by showing how observations of an extended stellar or planetary object carried out with a periodic grid may also yield valuable information on its size and on the light distribution over its surface. Several categories of objects may benefit from this kind of observation depending on the modulation period, the telescope focal length, and the signal-to-noise ratio that can be achieved. We discuss the overall principles of this method and derive an analytical formulation for the `modulation function' defined in the text. An application based on Hipparcos observations of the largest minor planet (1) Ceres is provided as an illustration of the method.