AAS Meeting #193 - Austin, Texas, January 1999
Session 47. Supernovae
Display, Thursday, January 7, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[47.08] Spectral Analysis of Circumstellar Wind Interaction in the Type~IIn Supernova 1998S

E.J. Lentz, E. Baron, D. Branch (University of Oklahoma), P.H. Hauschildt (University of Georgia), C. Fransson, P. Lundqvist (Stockholm Observatory), P. M. Garnavich, R. P. Kirshner (CfA), SINS Team

We analyze the effects of circumstellar interaction on spectra of the Type~IIn supernova 1998S obtained from the ground and with the HST by the SINS team. The narrow (~ 100 - 1000 km s-1) UV and Balmer lines are assumed to come from a thin circumstellar shell, and the broad (~000 - 10,000 km s-1), shallow features must have formed in the supernova. We have modeled the spectra using the general NLTE model-atmosphere and spectrum-synthesis code, PHOENIX. We find general agreement between observations and the model results, however, our models fail to reproduce the strong UV excess. The UV excess can be probably be explained by adding inverse Comptonization of the photospheric photons in the hot shocked gas in the interaction region between ejecta and the wind. A large mass loss rate seems to be needed. We have also explored the effects of external illumination from the shocks on the ejecta, and we find this to be important. We predict that SN 1998S will be a strong radio source, and that it should soon turn on at short radio wavelengths.


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