cosmic rays were removed, using the IRAF routine IMCOMBINE. The continuum images were scaled to foreground stars in the H$\alpha$+\[\]+continuum images, and then subtracted to produce line emission images. The images presented in this paper are each displayed with a logarithmic scaling, to emphasize faint emission and structure within the H$\alpha$ emission.

The line images were flux calibrated using the Oke & Gunn (1983) standard star HD 19445. We corrected for the slight effect of H$\alpha$ absorption in the standard star. The rms noise after calibration and continuum subtraction is $\sim$2 $\times$ 10$^{\rm
-17}$ ergs s$^{\rm -1}$ cm$^{\rm -2}$ pix$^{\rm -1}$. Expressed in emission measure (the integral of the electron density [*squared*]{} along the line of sight) this corresponds to 22 pc cm$^{\rm -6}$, assuming an electron temperature of 10,000 K (note that for ionized gas at 10,000 K, 5.6 $\times$ 10$^{\rm -18}$ erg s $^{\rm -1}$ cm$^{\rm -2}$ arcsec$^{\rm -2}$ = 2.8 pc cm$^{\rm -6}$ (e.g. WB92)). The accuracy of the calibration was tested by comparing the fluxes of several normal regions in overlapping fields between the 1997 data set and WB92. The fluxes in the 1997 data are higher by $\sim$30$\%$. Since the WB92 data did not contain 