Instrument Information
IDENTIFIER urn:nasa:pds:context:instrument:keck.10m_keck2.echelle::1.1
NAME KECK ECHELLE SPECTROGRAPH AND IMAGER
TYPE SPECTROMETER

IMAGER
DESCRIPTION The following information was extracted from the ''ESI: Echelle spectrograph and Imager'' user's manual available from the Keck IIweb site, at this URL (as of this writing): http://www2.keck.hawaii.edu/inst/esi/ESI_Manual.html Sections of the content of this manual website are reproduced withthe kind permission of Keck Observatory. Keck's Echelle Spectrograph and Imager (ESI) has three modes. In the echelle mode, there are ten orders on the CCD with complete wavelengthcoverage from 3900 Angstroms to 10900 Angstroms. The dispersion in Angstroms/pixelvaries from order to order, as does the spatial scale along the slit. The bluestorder (15) has a linear dispersion of ~0.15 Angstroms/pixel and the dispersionincreases moving towards the red (lower order number), inversely by the order number,up to 0.30 Angstroms/pixel (order 6). The scale in the dispersion direction is 0.154arcsec/pixel; 1 arcsec projects to 6.5 pixels. The velocity dispersion is a nearlyconstant 11.5 km/s/pixel in all orders. Slits are 20 arcseconds in length and areavailable with widths of 0.3, 0.5, 0.75, 1.0, 1.25 and 6.0 arcseconds. A onearcsecond wide slit projects to 6.5 pixels (0.154 arcsec/pixel). The free spectralrange of every order listed falls completely on the detector. The bluer orderscontain significant amounts of data outside the free spectral range as well.The low-resolution mode of ESI uses only the prisms for dispersion, and hasmulti-slit capability. The dispersion varies roughly linearly from 0.8Angstroms/pixel (60 km/sec/pixel) at 3900 Angstroms, to 11 Angstroms/pixel (300km/sec/pixel) at 11,000 Angstroms. The slit length is approximately 8 arcminutes, and0.3, 0.5, 0.75, 1.0, 1.25, and 6.0 arcsecond wide slits are available. There is noneed for order separation. Since the dispersion is done by prisms, there are nohigher order spectra as there are with gratings or grisms.The direct imaging mode of ESI has the prisms out of the beam and an imaging mirrorin place. In this mode, ESI delivers an 8 x 2 arcminute direct field. The facilityBVRI filters originally delivered are undersized with a field of 3.5 x 2.5arcminutes. The filters have been placed to allow the undersized facility filters toilluminate part of the CCD which is not affected by bad columns and is also more orless parallel to the rows and columns of the CCD. The unvignetted field is 2' x 8'with good images over the full field. R. Ellis has kindly donated a full-field Rfilter which is also available. During commissioning, images as good as 0.34" FWHMwere obtained.
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