An Optical Ultrahigh‐Resolution Cross‐dispersed Echelle Spectrograph with Adaptive Optics

A prototype cross-dispersed optical echelle spectrograph of very high resolution has been designed and built at Steward Observatory and tested at the Starfire Optical Range 1.5 m telescope. It is the first spectrograph to take advantage of diffraction-limited images provided by adaptive optics in order to achieve a potential resolving power of R ~ 600,000. The wavelength coverage in a single exposure is about 300 A, which is approximately 100 times that of conventional spectrographs operating at comparable resolution. This was achieved by recording 60 cross-dispersed orders across the 18 × 18 mm2 area of the CCD detector. The total efficiency of the system, including the sky and telescope transmission, spectrograph, and CCD detector, is measured to be 1.3% at peak, much higher than that of other ultrahigh-resolution spectrographs. Sample stellar spectra with R ~ 250,000 are presented.