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A Direct Measurement of Atmospheric Dispersion in N-band Spectra: Implications for Mid-IR Systems on ELTs

Abstract 144

Submitted by Andrew SKEMER


A. Skemer, L. Close, P. Hinz, W. Hoffmann


University of Arizona


Adaptive Optics will almost completely remove the effects of seeing at 10 microns on the ELT generation of telescopes. We show that the next most important limitation of image quality is atmospheric dispersion, rather than diffraction. By using the 6.5 meter MMT with its unique mid-IR adaptive optics system, we measure atmospheric dispersion in the N-band with the newly commissioned spectroscopic mode on MIRAC4. Our results indicate that atmospheric dispersion is generally linear in the N-band, although there is some residual curvature. We compare our measurements to theory, and make predictions for ELT Strehls and image FHWM with and without an atmospheric dispersion corrector (ADC). We find that for most mid-IR applications, an ADC will be necessary.