Interferometric Resolution Boosting for Spectrographs

Externally dispersed interferometry (EDI) is a technique for enhancing the performance of spectrographs for wide band-width high resolution spectroscopy and Doppler radial velocimetry. By placing a small angle-independent interferometer near the slit of a spectrograph, periodic fiducials are embedded on the recorded spectrum. The multiplication of the stellar spectrum times the sinusoidal fiducial net creates a moire ́ pattern, which manifests high detailed spectral information heterodyned down to detectably low spatial frequencies. The latter can more accurately survive the blurring, distortions and CCD Nyquist limitations of the spectrograph. Hence lower resolution spectrographs can be used to perform high res-olution spectroscopy and radial velocimetry. Previous demonstrations of ∼2.5 × resolution boost used an interferometer having a single fixed delay. We report new data indicating ∼6 × Gaussian resolution boost (140,000 from a spectrograph with 25,000 native resolving power), taken by using multiple exposures at widely different interferometer delays