Dartmouth College Dartmouth Digital Commons Dartmouth Scholarship Faculty Work 1999 Late-Time Optical and Ultraviolet Spectra of SN 1979C and SN 1980K Robert A. Fesen Dartmouth College Christopher L. Gerardy Dartmouth College Alexei V. Filippenko University of California at Berkeley Thomas Matheson University of California at Berkeley Roger A. Chevalier University of Virginia See next page for additional authors Follow this and additional works at: https://digitalcommons.dartmouth.edu/facoa Part of the Astrophysics and Astronomy Commons Dartmouth Digital Commons Citation Fesen, Robert A.; Gerardy, Christopher L.; Filippenko, Alexei V.; Matheson, Thomas; Chevalier, Roger A.; Kirshner, Robert P.; Schmidt, Brian P.; Challis, Peter; Fransson, Claes; Leibundgut, Bruno; and Van Dyk, Schuyler D., "Late-Time Optical and Ultraviolet Spectra of SN 1979C and SN 1980K" (1999). Dartmouth Scholarship. 2886. https://digitalcommons.dartmouth.edu/facoa/2886 This Article is brought to you for free and open access by the Faculty Work at Dartmouth Digital Commons. It has been accepted for inclusion in Dartmouth Scholarship by an authorized administrator of Dartmouth Digital Commons. For more information, please contact [email protected]. Authors 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 This article is available at Dartmouth Digital Commons: https://digitalcommons.dartmouth.edu/facoa/2886 THE ASTRONOMICAL JOURNAL, 117:725È735, 1999 February ( 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. LATE-TIME OPTICAL AND ULTRAVIOLET SPECTRA OF SN 1979C AND SN 1980K ROBERT A. FESEN,1 CHRISTOPHER L. GERARDY,1 ALEXEI V. FILIPPENKO,2 THOMAS MATHESON,2 ROGER A. CHEVALIER,3 ROBERT P. KIRSHNER,4 BRIAN P. SCHMIDT,5 PETER CHALLIS,4 CLAES FRANSSON,6 BRUNO LEIBUNDGUT,7 AND SCHUYLER D. VAN DYK8 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 Ha,[OI] 6300, 6364A ,A and [O II] 7319, 7330 . Weaker but similarly broad lines detected include [Fe II] 7155A ,A [S II] 4068, 4072 ,A and a blend of [Fe II] lines at 5050È5400 . The presence of strong [S II] 4068, 4072A emission but a lack of [S II] 6716, 6731A emission suggests electron densities of 105È106 cm~3. From the 1997 spectrum, we estimate an Ha Ñux of (1.3 ^ 0.2) ] 10~15 ergs cm~2 s~1, indicating a 25% decline from the 1987È1992 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 di†erent spectrum from that of SN 1980K. Broad, 6000 km s~1 emission lines are also seen but with weaker Ha, stronger [O III] 4959, 5007A , more highly clumped [O I] and [O II] line proÐles, no detectable [Fe II] 7155 A emission, and a faint but very broad emission feature near 5750A . A 1997 Hubble Space Telescope Faint Object Spectrograph, near-UV spectrum (2200È4500A )A shows strong lines of C II] 2324, 2325 , [O II] 2470A ,A and Mg II 2796, 2803 ,A along with weak [Ne III] 3969 ,A [S II] 4068, 4072 , and [O III] 4363 A emissions. The UV emission lines show a double-peak proÐle with the blueward peak substantially stronger than the red, suggesting dust extinction within the expanding ejecta [E(B[V ) \ 0.11È0.16 mag]. The lack of detectable [O II] 3726, 3729A emission, together with [O III] jj(4959 ] 5007)/ j4363 ^ 4, implies electron densities 106È107 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 speciÐc models that are available show several di†erences with the observations. High electron densities (105È107 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, 3729A ,A [N II] 6548, 6583 , and [S II] 6716, 6731A . Interaction models are needed that are speciÐcally suited to these supernovae. We review the overall observed range of late-time SNe II-L properties and brieÑy discuss their properties relative to young, ejecta-dominated Galactic supernova remnants. Key words: galaxies: individual (NGC 4321, NGC 6946) È supernovae: individual (SN 1979C, SN 1980K) 1. INTRODUCTION 6300, 6364A emission, along with weaker line emission from [Ca II] 7291, 7324A and/or [O II] 7319, 7330 A , The Type II linear supernova (SN II-L) SN 1980K in [O III] 4959, 5007A ,A and [Fe II] 7155 (FB90; Uomoto NGC 6946 reached a peak brightness of V \ 11.4 in 1980 1991; Leibundgut et al. 1991). Monitoring of its optical Ñux November (see Barbon, Ciatti, & Rosino 1982; Hurst & from 1988 through 1992 indicated a nearly constant lumi- Taylor 1986 and references therein). Despite a steadily nosity (Leibundgut, Kirshner, & Porter 1993; Fesen & declining Ñux through 1982 (Uomoto & Kirshner 1986), Matonick 1994, hereafter FM94). faint Ha emission from SN 1980K was detected in 1987 Following the optical recovery of SN 1980K, a handful of through narrow passband imaging (Fesen & Becker 1990, other SNe II-L have been optically detected 7È25 yr after hereafter FB90). Low-dispersion optical spectra obtained in maximum light. These include SN 1986E in NGC 4302 1988 and 1989 showed broad, 6000 km s~1 Ha and [O I] (Cappellaro et al. 1995), SN 1979C in M100 (Fesen & Matonick 1993), and SN 1970G in M101 (Fesen 1993). The ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ late-time optical spectra of all these SNe show broad Ha 1 Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755. and forbidden oxygen emission lines, and these character- 2 Department of Astronomy, University of California at Berkeley, istics have been exploited in searching for fainter, late-time Department of Astronomy, 601 Cambell Hall, Berkeley, CA 94720-3411. SNe II-L (e.g., SN 1985L in NGC 5033; Fesen 1998). 3 Department of Astronomy, University of Virginia, P.O. Box 3818, Of the few SNe II-L recovered at late times, SN 1979C in Charlottesville, VA 22903. M100 (NGC 4321) is particularly noteworthy. This SN was 4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138. exceptionally bright at outburst for a Type II event, with a [ 5 Mount Stromlo and Siding Spring Observatories, Australian Nation- peakMB of 20 mag (Young & Branch 1989; Gaskell al University, Private Bag, Weston Creek, ACT 2611, Australia. 1992) and became bright in the radio as well, eventually 6 Stockholm Observatory, SE 133 36Saltsjo baden, Sweden. reachinga6cmluminosity more than 200 times that of Cas 7 European Southern Observatory, Karl-Schwarzschild-Strasse 2, Gar- ching, 85748, Germany. A (Weiler et al. 1989). It also exhibits among the highest, 8 Infrared Processing and Analysis Center, California Institute of Tech- late-time Ha luminosity (D1 ] 1038 ergs s~1) and shows nology, Mail Stop 100-22, Pasadena, CA 91125. radio emission variability, which may be due to a periodic 725 726 FESEN ET AL. Vol. 117 modulation of the progenitorÏs pre-SN mass loss (Weiler et determine the wavelength scale and resolution (D10 A ). al. 1991). Flux calibration and removal of telluric absorption lines Late-time optical SN II emission lines are thought to were achieved with a spectrum of the sdF star BD arise from interactions with surrounding circumstellar ]17¡4708 (Oke & Gunn 1983). mass-loss material (CSM). These interactions lead to the A spectrum of SN 1980K was also obtained on 1997 formation of a reverse shock moving back into the expand- November 3 using the 2.4 m Hiltner telescope at the MDM ing ejecta, which then subsequently ionizes, either by Observatory on Kitt Peak. A modular spectrograph like far-UV or X-ray emission, a broad inner ejecta region from that in use at Las Campanas Observatory was employed which the optical lines are produced (Chevalier & Fransson with a north-south aligned2A.2] 4@ slit, a 600 line mm~1 1994, hereafter CF94). This model is also consistent with the 5000A blaze grating, and a 1024 ] 1024 Tektronics CCD presence of accompanying nonthermal radio emission in all detector. A single 6000 s exposure covering the spectral optically recovered SNe II-L, with radio light curves like region 4000È8500A was taken with a spectral resolution of those predicted from the ““ minishell ÏÏ model involving about 5A . Cosmic rays were removed using standard IRAF shock generated synchrotron emission from the forward routines for pixel rejection and replacement. Observing shock (Chevalier 1982; Weiler et al. 1993). conditions were photometric but due to slit light losses Late-time SN II emission lines are important for the caused by variable seeing during the long exposure, absol- information they can provide on SNe ejecta abundances, ute Ñuxes are reliable only to ^15%. late-time shock emission processes, and the mass-loss A spectrum of SN 1979C was obtained on 1993 May 21 history and evolutionary status of SN progenitors using the Red Channel long-slit CCD spectrograph (Leibundgut et al. 1991; Weiler et al. 1991; Montes et al. (Schmidt, Weymann, & Foltz 1989) on the 4.5 m Multiple 1998). Unfortunately, optical emission lines from old SNe Mirror Telescope (MMT). Three 1200 s exposures were II-L are quite faint (¹3 ] 10~17 ergs cm~2 s~1 A~1), taken using a 2@@ ] 180@@ slit and covering a spectral range making accurate measurements difficult even using 4 m 3800È9900A with 12A resolution.