NLTE treatment of calcium in the Monte Carlo modeling of early-time spectra of SN 1993J.

Abstract

NLTE treatment of calcium with five lower bound energy levels of Ca II and the ionization state of Ca III is annexed to the Monte Carlo model to improve our study on the early-time spectra of SN 1993J. This NLTE + Monte Carlo code is employed in modeling the ultraviolet and optical spectra of SN 1993J obtained simultaneously on 1993 April 15 by the HST and at Lick Observatory (Jeffery et al. 1994). With a solar composition of element abundances, most observed spectral lines are reproduced by a power law density structure of index around 22. Ca II lines such as Ca II H+K and infrared triplet are improved both in intensities and profiles compared with models without NLTE treatment. The NLTE study of calcium in early-time spectra of SN 1993J may also give information of the abundance of the element. Detailed calculations suggest that calcium may have only half of its solar composition in the outer atmosphere of SN 1993J.