TEIFU: a thousand element integral field unit for the WHT fed by the ELECTRA AO system

A description is given of the fiber based Thousand Element Integral Field Unit (TEIFU) that is being built by Durham University for use with the WYFFOS fiber spectrograph and the ELECTRA Adaptive Optics system at the William Herschel Telescope. With TEIFU there will be at least one thousand spatial elements with selectable sampling scales of 0.125, 0.25 and 0.5 arcsec corresponding to field areas of 14, 56 and 222 square arcsec, the field can be divided into 2 to facilitate background subtraction. The first two scales of 0.125 and 0.25 arcsec are designed to take advantage of the improved image quality provided by the ELECTRA AO system. The 0.5 arcsec sampling is designed for use without ELECTRA and samples the uncorrected image quality provided by the WHT. In this mode there is a larger field that is not constrained by the guide star requirement of the ELECTRA AO system. The operating wavelength of the system will be approximately 500 - 1000 nm.