THE LATE-TIME OPTICAL-SPECTRUM OF SN-1980K

Low-dispersion spectra of the Type II-L supernova 1980K taken in 1991 June and 1992 July/August are presented and compared to those obtained in 1988 and 1989. These spectra, covering the wavelength range 4600-9 400 angstrom, show broad Halpha and [O I] lambdalambda6300, 6364 emiss ion lines with flux levels similar to those seen in earlier spectra. T he blueward asymmetry of the Halpha line profile reported in 1988 data is not seen in the 1991/1992 spectra; however, a decrease in the Halp ha expansion velocity from 1988 to 1992 may have occurred. Broad and f aint emission near 5000 angstrom is interpreted as [O III] lambdalambd a4959, 5007. Strong emission at 7300 angstrom is likely to be [Ca II] lambdalambda7291, 7324 emission though some contribution from [O II] l ambdalambda7320, 7330 is possible. Emission near 7100 angstrom, report ed in one 1988 spectrum but unconfirmed in two 1989 spectra, is now cl early detected and is identified as probably [Fe II] lambda7155. SN 19 80K's Halpha and [O I] line fluxes over the last 4 years appear remark ably steady. Comparison with line emission predictions from late-time circumstellar interaction models show generally good agreement. Howeve r, some predicted line emission changes, notably a steep decline in Ha lpha flux, are not observed. If SN 1980K's Halpha flux stays near its current level of 1.7 x 10(-15) ergs cm-2 s-1, useful optical spectra s hould remain possible for several more years. Continued spectral monit oring will help constrain late-time energy source models for Type II S Ns and permit the investigation of this supernova's early remnant deve lopment.