Narrow Lines in Type II Supernovae: Probing the Circumstellar Nebulae of the Progenitors

We have carried out a high-dispersion (R~30,000) echelle spectroscopic surveyof 16 Type II supernovae (SNe) to search for narrow emission lines fromcircumstellar nebulae ejected by their massive progenitors. Circumstellarnebulae, if detected, provide invaluable opportunities to probe SN progenitors.Of the 16 SNe observed, SN ejecta are clearly detected in 4 SNe and possibly inanother 2 SNe, interstellar gas is detected in 12 SNe, and circumstellarmaterial is detected only in SN 1978K and SN 1998S. In the case of SN 1978K weare able to place an upper limit of ~2.2 pc for the size of the circumstellarejecta nebula and note that this is more consistent with the typical sizesobserved for ejecta nebulae around luminous blue variables rather thanWolf-Rayet stars. In the case of SN 1998S, our observations of the narrow lines\~1 year after the SN explosion show variations compared to early epochs. Thenebular lines we observe from SN 1998S originate from either the low--density,outer region of a circumstellar nebula or have become dominated by aninterstellar component.Comment: (20 pages, 7 figures, revised from previous version, resubmitted to AJ, 28 Jan 2002