Quantification of the expected residual dispersion of the MICADO Near-IR imaging instrument

Abstract

MICADO, a near-infrared imager for the Extremely Large Telescope, is being designed to deliver diffraction limited imaging and 50 micro arcsecond ($\mu$as) astrometric accuracy. MICADO employs an atmospheric dispersion corrector (ADC) to keep the chromatic elongation of the point spread function (PSF) under control. We must understand the dispersion and residuals after correction to reach the optimum performance. Therefore, we identified several sources of chromatic dispersion that need to be considered for the MICADO ADC. First, we compared common models of atmospheric dispersion to investigate whether these models remain suitable for MICADO. We showed that the differential dispersion between common atmospheric models and integration over the full atmosphere is less than 10 $\mu$as for most observations in H-band. We then performed an error propagation analysis to understand the uncertainty in the atmospheric dispersion as a function of atmospheric conditions. In addition, we investigated the impact of photometric color on the astrometric performance. While the differential refraction between stars within the same field of view can be significant, the inclusion of an ADC rendered this effect negligible. For MICADO specifically, we found that the current optomechanical design dominates the residual dispersion budget of 0.4 milli arcseconds (mas), with a contribution of 0.31 mas due to the positioning accuracy of the prisms and up to 0.15 mas due to a mismatch between the dispersive properties of the glass and the atmosphere. We found no showstoppers in the design of the MICADO ADC for achieving 50 $\mu$as relative astrometric accuracy.

Submitted to Monthly Notices of the Royal Astronomical Society. Contains 11 pages and 12 figures

References in corpus (5)

• Refractive Index of Humid Air in the Infrared: Model Fits
• Atmospheric Refractive Electromagnetic Wave Bending and Propagation Delay
• MICADO: first light imager for the E-ELT
• Zenith-Distance Dependence of Chromatic Shear Effect: A Limiting Factor for an Extreme Adaptive Optics System
• High-precision astrometry towards ELTs

Cited by in corpus (3)

• Computation of the lateral shift due to atmospheric refraction
• Towards Realistic Modeling of the Astrometric Capabilities of MCAO Systems: Detecting an Intermediate Mass Black Hole with MAVIS
• Demonstration of an imaging technique for the measurement of PSF elongation caused by Atmospheric Dispersion