Adaptive optics echelle spectrograph for radial velocity studies

Radial velocity studies represent the most successful method to date for the detection of extrasolar planets. Although radial velocity (vr) measurement precision of 3 m s-1 is routinely achieved in some programs, it is important to understand and minimize sources of experimental error. Furthermore, velocity variations resulting from astrophysical processes contribute to velocity errors, and must be removed if precision is to be further improved. The use of spectrographs with telescopes having high order adaptive optics (AO) systems offers the possibility of achieving near diffraction-limited very high spectral resolution at visible wavelengths on ground-based telescopes. The small stellar image diameters obtained with adaptively corrected systems allow high resolution without a large loss of light at the spectrograph entrance aperture. The Adaptively Corrected Echelle Spectrograph (ACES), designed at Steward Observatory for a spectral resolution R ~ 200,000, couples the telescope image to the instrument with an 8-10μm diameter near single-mode optical fiber. The shorter effective slit permits the placement of more echelle orders on the detector after cross dispersion, with a correspondingly greater wavelength coverage per exposure. This simultaneous high resolution and large wavelength coverage can be used to improve the precision of radial velocity studies by improving wavelength calibration, reducing dataset internal errors, and permitting better characterization and removal of effects intrinsic to the stars themselves.