Atmospheric effects on astrometry

The turbulent behavior of the atmosphere causes jitter in the apparent position of sources on short (subsecond) timescales. This thus limits achievable astrometric accuracy. The adaptive optics system counters the turbulent behavior by determining and applying a real-time a correction to mirror shapes that optimizes the spatial resolution optimally at a single location in the FoV. Away from this point the correction also has an effect, but corrects less optimal.

Current image simulations for MICADO at the E-ELT take as input simualated atmospheres based on extensive measurements of atmsopheric turbulence properties (e.g., Sarazin et al., 2013.

Adaptive optics system optimize for image spatial resolution, not for astrometric accuracy. The combined effect of atmospheric turbulence and deformation of mirrors has a complex impact on astrometry. Studies on the impact of atmospheric turbulence on astrometry are limited.