Design and performance of a new generation, compact, low cost, very high Doppler precision and resolution optical spectrograph

摘要

This paper is to report the design and performance of a very high Doppler precision cross-dispersedechelle spectrograph, EXtremely high Precision ExtrasolaR planet Tracker III (EXPERT-III), as part of aglobal Exoplanet Tracker (ET) network. The ET network is designed to hunt low mass planets, especiallyhabitable rocky planets, around GKM dwarfs. It has an extremely high spectral resolution (EHR) mode ofR=110,000 and a high resolution (HR) mode of R=56,000 and can simultaneously cover 0.38-0.9 μmwith a 4kx4k back-illuminated Fairchild CCD detector with a single exposure. EXPERT-III is optimizedfor high throughput by using two-prisms cross-disperser and a large core diameter fiber (2 arcsec on sky,or 80 μm at f/4) to collect photons from the Kitt Peak National Observatory (KPNO) 2.1m telescope. Theaverage overall detection efficiency is ~6% from above the atmosphere to the detector for the EHR Modeand about 11% for the HR mode. The extremely high spectral resolution in a compact design (thespectrograph dimension, 1.34x0.8x0.48 m) is realized by coupling the single input 80 μm telescope fiberinto four 40 μm fibers and re-arranging the four small core diameter fibers into a linear fiber slit array (aone-to-four fiber image slicer). EXPERT-III is operated in a vacuum chamber with temperature controlledto ~2 milli-Kelvin rms for an extended period of time. The radial velocity (RV) drift is controlled towithin 10 meters/second (m/s) over a month. EXPERT-III can reach a photon noise limited RVmeasurement precision of ~0.3 m/s for a V=8 mag GKM type dwarf with small rotation (vsini =2 km/s) ina 15 min exposure. EXPERT-III’s RV measurement uncertainties for bright stars are primarily limited bythe Thorium-Argon (ThAr) calibration source (~0.5 m/s). EXPERT-III will serve as an excellent publicaccessible high resolution optical spectroscope facility at the KPNO 2.1m telescope.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.