The optical/UV light curves of SN 1987A are analyzed with the multienergy group radiation hydrodynamics code STELLA. The calculated monochromatic and bolometric light curves are compared with observations shortly after shock breakout, during the early plateau, through the broad second maximum, and during the earliest phase of the radioactive tail. We have concentrated on a progenitor model calculated by Nomoto & Hashimoto and Saio, Nomoto, & Kato, which assumes that 14 of the stellar M _ mass is ejected. Using this model, we have updated constraints on the explosion energy and the extent of mixing in the ejecta. In particular, we determine the most likely range of E/M (explosion energy over ejecta mass) and (radius of the progenitor). In general, our best models have energies in the range R 0 E \ (1.1^0.3) ] 1051 ergs, and the agreement is better than in earlier, Ñux-limited di †usion calculations for the same explosion energy. Our modeled B and V Ñuxes compare well with observations, while the Ñux in U undershoots after D10 days by a factor of a few, presumably owing to NLTE and line transfer e †ects. We also compare our results with IUE observations, and a very good quantitative agreement is found for the Ðrst days, and for one IUE band (2500È3000 as long as for 3 months. We point out A ) that the V Ñux estimated by McNaught & Zoltowski should probably be revised to a lower value.

The light curve of supernova (SN) 1993J is calculated using two approaches to radiation transport as exempliÐed by the two computer codes, STELLA and EDDINGTON. Particular attention is paid to shock breakout and the photometry in the U, B, and V bands during the Ðrst 120 days. The hydrodynamical model, the explosion of a 13 star that has lost most of its hydrogenic envelope to a com-M _ panion, is the same in each calculation. The comparison elucidates di †erences between the approaches and also serves to validate the results of both. STELLA includes implicit hydrodynamics and is able to model supernova evolution at early times, before the expansion is homologous. STELLA also employs multigroup photonics and is able to follow the radiation as it decouples from the matter. EDDINGTON uses a di †erent algorithm for integrating the transport equation, assumes homologous expansion, and uses a Ðner frequency resolution. Good agreement is achieved between the two codes only when compatible physical assumptions are made about the opacity. In particular, the line opacity near the principal (second) peak of the light curve must be treated primarily as absorptive, even though the electron density is too small for collisional deexcitation to be a dominant photon destruction mechanism. JustiÐcation is given for this assumption and involves the degradation of photon energy by "" line splitting,ÏÏ i.e., Ñuores-cence. The fact that absorption versus scattering matters to the light curve is indicative of the fact that departures from equilibrium radiative di †usion are important. A new result for SN 1993J is a prediction of the continuum spectrum near the shock breakout (calculated by STELLA), which is superior to the results of other standard single energy group hydrocodes such as VISPHOT or TITAN. Based on the results of our independent codes, we discuss the uncertainties involved in the current time-dependent models of supernova light curves.

ABSTRACT. We have studied the association of supemovae in spiral galaxies with sites of recent star formation-spiral arms and HII regions. It is shown that supemovae (SNe) of Types la, lb, and II exhibit concentration to spiral arms and their distributions over the distance to the nearest spiral arm do not differ significantly. This result is confirmed by a Kolmogorov-Smimov test comparison with the distance distributions, expected if SNe are distributed randomly inside the model galaxy. SNe of Types lb and II show a strong concentration towards HII regions, while distribution of SNe la can be explained by chance superposition. All studied distributions of SNe lb and II show striking similarity, which suggests that their progenitors are massive stars with similar ages and initial masses. The association of SNe la with spiral arms suggests that their progenitors in spiral galaxies are likely to be intermediate mass stars.

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