The impact of ELT distortions and instabilities on future astrometric observations

Abstract

The paper discusses an assessment study about the impact of the distortions on the astrometric observations with the Extremely Large Telescope originated from the optics positioning errors and telescope instabilities. Optical simulations combined with Monte Carlo approach reproducing typical inferred opto-mechanical and dynamical instabilities, show RMS distortions between $\sim$ 0.1-5 mas over 1 arcmin field of view. Over minutes timescales the plate scale variations from ELT-M2 caused by wind disturbances and gravity flexures and the field rotation from ELT-M4-M5 induce distortions and PSF jitter at the edge of 1 arcmin FoV (radius 35 arcsec) up to $\sim$ 5 mas comparable to the diffraction-limited PSF size $FWH{M}_H=8.5$ mas. The RMS distortions inherent to the ELT design are confined to the 1${}^{st}$-3${}^{rd}$ order and reduce to an astrometric RMS residual post fit of $\sim$ 10-20 $\mu as$ for higher order terms. In this paper, we study which calibration effort has to be undertaken to reach an astrometric stability close to this level of higher order residuals. The amplitude and timescales of the assumed telescope tolerances indicate the need for frequent on-sky calibrations and MCAO stabilization of the plate scale to enable astrometric observations with ELT at the level of $\le 50\mu as$, which is one of the core science missions for the ELT / MICADO instrument.

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Cited by in corpus (8)

• Microarcsecond Astrometry: Science Highlights from Gaia
• Unveiling the nature of the Gemini multiconjugate adaptive optics system distortions
• Towards Realistic Modeling of the Astrometric Capabilities of MCAO Systems: Detecting an Intermediate Mass Black Hole with MAVIS
• Development of the Warm Astrometric Mask for MICADO astrometry calibration
• The impact of geometric distortions in multiconjugate adaptive optics astrometric observations with future extremely large telescopes
• Lessons learned from SPHERE for the astrometric strategy of the next generation of exoplanet imaging instruments
• Adaptive Optics for the Extremely Large Telescope: overcoming Point Spread Function challenges with MORFEO
• The MICADO first light imager for ELT: its astrometric performance