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Deep interference-filter images obtained from the Burrell Schmidt telescope and S2KA CCD at KPNO have been assembled into $2\deg \times 2\fdg 6$\ mosaics covering almost the entire galaxy at a scale of 2 arcsec pixel$^{-1}$. Our mosaics comprise 23 individual frames each in \ha\ and \sii\ $\lambda\ 6724$\ emission lines and in a red continuum band, and they represent total exposure times of 6, 8, and 4 hrs, respectively. The combined images have been corrected for sky curvature to give images that are astrometrically accurate to 2\arcsec\ or better over the entire field and that appear virtually seamless, despite the fact that observations were made over three seasons under varying sky conditions. The continuum mosaic has been scaled and subtracted from the emission-line ones, to give images that reveal faint nebulous structures throughout the galaxy. Typica l rms noise in the continuum-subtracted images is $6 \times 10^{-17} \ \:{\rm ergs\:cm^{-2} \:s^{-1} \:pixel^{-1}}$. We will present large-scale images of M31 and will outline our technique for assembling the mosaics, using adapted versions of standard IRAF tasks. The deep images in pure emission lines enable us to identify a large number of candidate supernova remnants and other gaseous nebulae; preliminary results are presented in a companion paper.
Observations were made with the Burrell Schmidt telescope of the Warner and Swasey Observatory, Case Western Reserve University. This research is sponsored by NSF grant AST-9315967 and by the Keck Northeast Astronomy Consortium.
