Abstract:
Supernova (SN) 1987A was classified as a peculiar Type II SN because of its long rising light curve and the persistent presence of HI lines in optical spectra. It was subsequently realized that its progenitor was a blue supergiant (BSG), rather than a red supergiant (RSG) as for normal, Type II-P, SNe. Since then, the number of Type II-pec SNe has grown, revealing a rich diversity in photometric and spectroscopic properties. In this study, using a single 15Msun low-metallicity progenitor that dies as a BSG, we have generated explosions with a range of energies and 56Ni masses. We then performed the radiative transfer modeling with CMFGEN, from 1d until 300d after explosion for all ejecta. Our models yield light curves that rise to optical maximum in about 100d, with a similar brightening rate, and with a peak absolute V-band magnitude spanning -14 to -16.5mag. All models follow a similar color evolution, entering the recombination phase within a few days of explosion, and reddening further until the nebular phase. Their spectral evolution is analogous, mostly differing in line width. With this model set, we study the Type II-pec SNe 1987A, 2000cb, 2006V, 2006au, 2009E, and 2009mw. The photometric and spectroscopic diversity of observed SNe II-pec suggests that there is no prototype for this class. All these SNe brighten to maximum faster than our limited set of models, except perhaps SN 2009mw. The spectral evolution of SN 1987A conflicts with other observations in this set and conflicts with model predictions from 20 d until maximum: Halpha narrows and weakens while BaII lines strengthen faster than expected, which we interpret as signatures of clumping. SN 2000cb rises to maximum in only 20d and shows weak BaII lines. Its spectral evolution (color, line width and strength) is well matched by an energetic ejecta but the light curve may require strong asymmetry. The persistent blue color, narrow lines, and weak Halpha absorption, seen in SN 2006V conflicts with expectations for a BSG explosion powered by 56Ni and may require an alternative power source. In contrast with theoretical expectations, observed spectra reveal a diverse behavior for lines like BaII 6142 Å, NaID, and Halpha. In addition to diversity arising from different BSG progenitors, we surmise that their ejecta are asymmetric, clumped, and, in some cases, not solely powered by 56Ni decay.

The full paper is available here

To access the spectra for some of these models, click on the following links (each zipped tar file contains the multi-epoch spectra and a list relating model index to the time since explosion):

a2.tgz
a3.tgz
a3m.tgz
a3ni.tgz
a4.tgz
a4he.tgz
a4ni.tgz
a5.tgz