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For refcode 1999AJ....117..725F:
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Copyright by American Astronomical Society. Reproduced by permission
1999AJ....117..725F LATE-TIME OPTICAL AND ULTRAVIOLET SPECTRA OF SN 1979C AND SN 1980K ROBERT A. FESEN, CHRISTOPHER L. GERARDY, ALEXEI V. FILIPPENKO, THOMAS MATHESON, ROGER A. CHEVALIER, ROBERT P. KIRSHNER, BRIAN P. SCHMIDT, PETER CHALLIS, CLAES FRANSSON, BRUNO LEIBUNDGUT, AND SCHUYLER D. VAN DYK Received 1998 October 21; accepted 1998 October 28 ABSTRACT A low-dispersion Keck I spectrum of SN 1980K taken in 1995 August (t = 14.8 yr after explosion) and a spectrum taken in 1997 November (t = 17.0 yr) at the MDM Observatory show broad 5500 km s^-1^ emission lines of H{alpha}, [OI] 6300, 6364 E, and [O II] 7319, 7330 E. Weaker but similarly broad lines detected include [Fe II] 7155 E, [S II] 4068, 4072 E, and a blend of [Fe II] lines at 5050-5400 E. The presence of strong [S II] 4068, 4072 E emission but a lack of [S II] 6716, 6731 E emission suggests electron densities of 10^5^-10^6^ cm^-3^. From the 1997 spectrum, we estimate an H{alpha} flux of (1.3 +/- 0.2) x 10^-15^ ergs cm^-2^ s^-1^, indicating a 25% decline from the 1987-1992 levels during the period 1994 to 1997, possibly related to a reported decrease in its nonthermal radio emission. A 1993 May, Multiple Mirror Telescope spectrum of SN 1979C (t = 14.0 yr) shows a somewhat different spectrum from that of SN 1980K. Broad, 6000 km s^-1^ emission lines are also seen but with weaker H{alpha}, stronger [O III] 4959, 5007 E, more highly clumped [O I] and [O II] line profiles, no detectable [Fe II] 7155 E emission, and a faint but very broad emission feature near 5750 E. A 1997 Hubble Space Telescope Faint Object Spectrograph, near-UV spectrum (2200-4500 E) shows strong lines of C II] 2324, 2325 E, [O II] 2470 E, and Mg II 2796, 2803 E, along with weak [Ne III] 3969 E, [S II] 4068, 4072 E, and [O III] 4363 E emissions. The UV emission lines show a double-peak profile with the blueward peak substantially stronger than the red, suggesting dust extinction within the expanding ejecta [E(B-V) = 0.11-0.16 mag]. The lack of detectable [O II] 3726, 3729 E emission, together with [O III]{lambda}{lambda}(4959 + 5007)/{lambda}4363 ~ 4, implies electron densities 10^6^-10^7^ cm^-3^. These Type II linear supernovae (SNe II-L) spectra show general agreement with the lines expected in a circumstellar interaction model, but the specific models that are available show several differences with the observations. High electron densities (10^5^-10^7^ cm^-3^) result in stronger collisional de-excitation than assumed in the models, thereby explaining the absence of several moderate to strong predicted lines such as [O II] 3726, 3729 E, [N II] 6548, 6583 E, and [S II] 6716, 6731 E. Interaction models are needed that are specifically suited to these supernovae. We review the overall observed range of late-time SNe II-L properties and briefly discuss their properties relative to young, ejecta- dominated Galactic supernova remnants. Key words: galaxies: individual (NGC 4321, NGC 6946)-supernovae: individual (SN 1979C, SN 1980K)
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