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Optical CCD imaging and spectroscopic observations of three supernovaremnants are presented. Optical emission from G 54.4-0.3 and G 59.8+1.2 isdetected for the first time, while the first flux calibrated CCD images of thesupernova remnant G 126.2+1.6 were performed in the optical emission lines ofHalpha+[N II], [O III] and [S II]. A mixture of filamentary and diffusestructures is observed in G 54.4-0.3 and G 59.8+1.2, mainly in Halpha+[N II],while the deep optical images of G 126.2+1.6 reveal several new filamentary anddiffuse structures inside the extent of the remnant as defined by its knownradio emission. In all cases, the radio emission is found to be well correlatedwith the optical filaments. [O III] emission was not detected at G 54.4-0.3 andG 59.8+1.2 while in G 126.2+1.6, significant morphological differences betweenthe low and medium ionization images are present suggesting incomplete shockstructures. Deep long-slit spectra were taken at different positions of theremnants. Both the flux calibrated images and the long-slit spectra clearlyshow that the emission originates from shock-heated gas, while some spectra ofG 126.2+1.6 are characterized by large [O III]/Hbeta ratios. This remnant's [OIII] flux suggests shock velocities into the interstellar "clouds" between 100and 120 km/s, while the [O III] absence in the other two remnants indicatesslower shock velocities. For all remnants, the [S II]6716/6731 ratio indicateselectron densities below 600 cm^{-3} with particularly low densities for G54.4-0.3 (below 50 cm^{-3}). Finally, the Halpha emission has been measured tobe between 3.0 to 15.2x10^{-17} erg/s/cm^2/ arcsec^2, 3.2x10^{-17} erg/s/cm^2/arcsec^2 and between 6.5 to 16.8x10^{-17} erg/s/cm^2/ arcsec^2 for G 54.4-0.3,G 59.8+1.2 and G 126.2+1.6, respectively.Comment: 10 pages, 7 figures, accepted for publication in A&

Deep optical observations of the supernova remnants G 126.2+1.6, G 59.8+1.2 and G 54.4-0.3