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Published February 10, 1999 | Published + Submitted
Journal Article Open

Detection of Preshock Dense Circumstellar Material of SN 1978K


The supernova SN 1978K has been noted for its lack of emission lines broader than a few thousand kilometers per second since its discovery in 1990. Modeling of the radio spectrum of the peculiar SN 1978K indicates the existence of H II absorption along the line of sight. To determine the nature of this absorbing region, we have obtained a high-dispersion spectrum of SN 1978K at the wavelength range 6530-6610 Å. The spectrum shows not only the moderately broad Hα emission of the supernova ejecta but also narrow nebular Hα and [N II] emission. The high [N II] λ6583/Hα ratio, 0.8-1.3, suggests that this radio-absorbing region is a stellar ejecta nebula. The expansion velocity and emission measure of the nebula are consistent with those seen in ejecta nebulae of luminous blue variables. Previous low-dispersion spectra have detected a strong [N II] λ5755 line, indicating an electron density of (3–12) × 10^5 cm^(-3). We argue that this stellar ejecta nebula is probably part of the preshock dense circumstellar envelope of SN 1978K. We further suggest that SN 1997ab may represent a young version of SN 1978K.

Additional Information

© 1999. The American Astronomical Society. Received 1998 October 19; accepted 1998 December 11; published 1999 January 13. We would like to thank the referee for useful suggestions to improve this Letter. Y. H. C. acknowledges the support of NASA Long-Term Space Astrophysics grant NAG5-3246. M. J. M. and K. W. W. wish to thank the Office of Naval Research for the 6.1 funding supporting this research.

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