The TEDI (TripleSpec - Exoplanet Discovery Instrument) is the first instrument dedicated to the near infrared radial velocity search for planetary companions to low-mass stars. The TEDI uses Externally Dispersed Interferometry (EDI), a combination of interferometry and multichannel dispersive spectroscopy. We have joined a white-light interferometer with the Cornell TripleSpec (0.9 - 2.4 mu m) spectrograph at the Palomar Observatory 200 '' telescope and begun an experimental program to establish both the experimental and analytical techniques required for precision IR velocimetry and the Doppler-search for planets orbiting low mass stars and brown dwarfs.

The TEDI (TripleSpec Exoplanet Discovery Instrument) will be the first instrument fielded specifically for finding low-mass stellar companions. The instrument is a near infra-red interferometric spectrometer used as a radial velocimeter. TEDI joins Externally Dispersed Interferometery (EDI) with an efficient, medium-resolution, near IR (0.9 - 2.4 micron) echelle spectrometer, TripleSpec, at the Palomar 200 telescope. We describe the instrument and its radial velocimetry demonstration program to observe cool stars.

Externally Dispersed Interferometry (EDI) is the series combination of a fixed-delay field-widened Michelson interferometer with a dispersive spectrograph. This combination boosts the spectrograph performance for both Doppler velocimetry and high resolution spectroscopy. The interferometer creates a periodic spectral comb that multiplies against the input spectrum to create moire fringes, which are recorded in combination with the regular spectrum. The moire pattern shifts in phase in response to a Doppler shift. Moire patterns are broader than the underlying spectral features and more easily survive spectrograph blurring and common distortions. Thus, the EDI technique allows lower resolution spectrographs having relaxed optical tolerances (and therefore higher throughput) to return high precision velocity measurements, which otherwise would be imprecise for the spectrograph alone.

The TEDI (TripleSpec Externally Dispersed Interferometry) is an interferometric spectrometer that will be used to explore the population of planets around the lowest mass stars. The instrument, to be deployed on the Palomar 200 Cassegrain mount, includes a stabilized Michelson interferometer combined with a medium resolution, broad band (0.8 - 2.4 micron) spectrograph, TripleSpec. We describe the instrument design and its application to Doppler velocimetry and high-resolution spectroscopy.

An externally dispersed interferometer (EDI) is a series combination of a fixed delay interferometer and an external grating spectrograph. We describe how the EDI can boost the effective resolving power of an echelle or linear grating spectrograph by a factor of 2 - 3 or more over the spectrograph's full bandwidth. The interferometer produces spectral fringes over the entire spectrograph's bandwidth. The fringes heterodyne with spectral features to provide a low spatial frequency moire pattern. The heterodyning is numerically reversed to recover highly detailed spectral information unattainable by the spectrograph alone. We demonstrate resolution boosting for stellar and solar measurements of two-dimensional echelle and linear grating spectra. An effective spectral resolution of similar to 100,000 has been obtained from the similar to 50,000 resolution Lick Observatory two-dimensional echelle spectrograph, and that of similar to 50,000 from an similar to 20,000 resolution linear grating spectrograph.