Estimation of Confusion in SIM Targets With a Detailed Focal Plane Model

摘要

The Space Interferometry Mission is an unique interferometer capable of performing narrow and wide angle astrometry on a few thousands of stars, distributed all over the Galaxy. It will be designed to achieve a single epoch precision of 10 micro arc seconds and an end of mission accuracy of 4 micro arc seconds in position and a similar accuracy in parallax and proper motions. The presence of confusing background and foreground stars might impose a limitation on the astrometric accuracy. We estimate the expected single measurement position uncertainty of the targets, owing to the presence of the confusing stars, from the knowledge of the dispositions and the spectral energy distributions (SEDs) of the stars within and just outside the field-of-view (FOV) of SIM. Our model also includes details of the instrumental parameters and the measurement process. The estimated uncertainties can in turn be used to correct the bias in the single measurement astrometric delay and, thus the final astrometric accuracy can be improved. We estimate the offsets from the zero delay position of the instrument and the projected separation of the components of binary stars in an elemental observation, following an one-dimensional synthesis imaging approach and a model fit to the absolute visibility data. These simulations help us to explore the strategies that can be followed to extract the details of the field through suitable model parameters in future.