Performance characteristics of the new Keck Observatory echelle spectrograph and imager

摘要

The Echelle Spectrograph and Imager (ESI) is a multipurpose instrument whichhas been delivered by the Instrument Development Laboratory of Lick Observatoryfor use at the Cassegrain focus of the Keck II telescope. ESI saw first lighton August 29, 1999. The optical performance of the instrument has been measuredusing artificial calibration sources and starlight. Measurements of the averageimage FWHM in echelle mode are 22 microns (0.22 arcseconds), 16 to 18 microns(0.16 to 0.18 arcseconds) in broad band imaging mode, and comparable in thelow-dispersion prismatic mode (LDP). Images on the sky, under best seeingconditions show FWHM sizes of 34 microns (0.34 arcseconds). Maximumefficiencies are measured to be 30% for echelle and anticipated to be greaterthan 38% for low dispersion prismatic mode including atmospheric, telescope anddetector losses. In this paper we describe the instrument and itsspecifications. We discuss the testing that led to the above conclusions.