CHIRON—A Fiber Fed Spectrometer for Precise Radial Velocities

The CHIRON optical high-resolution echelle spectrometer was commissioned at the 1.5m telescope at CTIO in 2011. The instrument was designed for high throughput and stability, with the goal of monitoring radial velocities of bright stars with high precision and high cadence for the discovery of low-mass exoplanets. Spectral resolution of R=79,000 is attained when using a slicer with a total (including telescope and detector) efficiency of 6% or higher, while a resolution of R=136,000 is available for bright stars. A fixed spectral range of 415 to 880 nm is covered. The echelle grating is housed in a vacuum enclosure and the instrument temperature is stabilized to +-0.2deg. Stable illumination is provided by an octagonal multimode fiber with excellent light-scrambling properties. An iodine cell is used for wavelength calibration. We describe the main optics, fiber feed, detector, exposure-meter, and other aspects of the instrument, as well as the observing procedure and data reduction.