THE CALIBRATION OF THE EUVE SPECTROMETERS .1. WAVELENGTH CALIBRATION AND RESOLUTION

We describe the wavelength calibration of the Extreme Ultraviolet Expl orer (EUVE) spectrometers and measurements of the spectrometers' resol ution. The three spectrometers operate in the wavelength range from 70 to 760 Angstrom with a resolving power of similar to 300. We present the equations required to map each detected photon to a wavelength and imaging angle. The equations depend on the position of the source on the sky, the orientation of the spacecraft when the photon arrives, an d the position on the EUVE detectors where the photon arrives. These e quations were determined using a ray-traced model of the EUVE spectrom eters along with measurements of emission lines and continua obtained both in prelaunch laboratory calibration and from observations of stel lar sources while in orbit. We describe the procedures used to apply t he equations in this paper to actual spectrometer data. We also discus s the implications of the results of this calibration for the analysis of the spectral images and suggest aperture sizes for spectral extrac tion. With this calibration, we can remap detected photons with rms er rors of 0.22 resolution elements (0.11 Angstrom) in the short waveleng th (SW) spectrometer, 0.13 elements (0.13 Angstrom) in the medium wave length (MW) spectrometer, and 0.13 elements (0.25 Angstrom) in the lon g wavelength (LW) spectrometer. The imaging angles for any one observa tion have rms errors of 4.8'' (1.1 pixel) in the SW spectrometer, 3.3' ' (0.7 pixel) in the MW spectrometer, and 2.9'' (0.6 pixel) in the LW spectrometer.