The supernova 1998S in NGC 3877: Another supernova with Wolf-Rayet star features in pre-maximum spectrum | Astronomy and Astrophysics Supplement Series

Astron. Astrophys. Suppl. Ser. 144, 219-225 (2000)

¹ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
² National Astronomical Observatories, Chinese Academy of Sciences, China
³ Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁴ Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China

Send offprint request to: Q.-Z. Liu, e-mail: qzliu@astro.uva.nl

Received: 3 January 2000
Accepted: 17 February 2000

Abstract

We present the BVR photometry and the spectra of SN 1998S taken about four months after discovery, beginning a week and 6 days before maximum brightness respectively. The light curves show a steep and linear decline, which are consistent with those of SN 1979C and are typical of a SN II-L. An absolute magnitude at maximum is derived, which is more than 2 mag brighter than the regular SNII and indicates this SN is a member of the rare class of Bright SNII. The color evolution at early epoch is also typical of linear SN II with a maximum () value of +1.35, similar to the typical Type II-L SN 1980K.
The spectral evolution is typical for SN II-L, very similar to that of the SN 1979C. They, however, showed some differences. The spectrum before maximum showed high-ionization N III and He II emission lines superposed on a strong blue continuum. Around the maximum light the high-ionization emission lines disappeared, leaving weak H I, He I emission lines, which are similar to those of SN 1983K. The extraordinary feature on the post-maximum spectra is the narrow emission P Cygni profile superposed on a much broader P Cygni structure in all five Balmer lines, Hα to Hϵ. Such feature is reminiscent of the post-maximum spectra of SN 1984E. 
Rapid spectral and photometric evolution, together with the presence of obvious P Cygni profile, suggests that SN 1998S is more consistent with the nature of a type II-L supernova than that of a IIn supernova, although narrow lines are present on the premaximum spectrum.


Key words: supernovae: general / supernovae: individual (SN 1998S)