The nature of SN 1997D: low-mass progenitor and weak explosion

We analyzed the spectra and light curve of the peculiar type II-P supernova 1997D to recover ejecta parameters. The optimal hydrodynamical model of SN 1997D, which meets observational constraints at the photospheric epoch, suggests a low explosion energy of about 10"5"0 erg, ejecta mass around 6 M_sun, and presupernova radius near 85 R_sun. We confirm the previous result by Turatto et al. (1998) that the ejecta contain a very low amount of radioactive "5"6Ni (#approx#0.002 M_sun). Modelling the nebular spectrum supports the hydrodynamical model and permits us to estimate the mass of freshly synthesized oxygen (0.02-0.07 M_sun). Combined with the basic results of stellar evolution theory the obtained parameters of SN 1997D imply that the progenitor was a star from the 8-12 M_sun mass range at the main sequence. The fact that at least some progenitors from this mass range give rise to core-collapse supernovae with a low kinetic energy (#approx#10"5"0 erg) and low amount of radioactive "5"6Ni (#approx#0.002 M_sun) has no precedent and imposes important constraints on the explosion mechanism. We speculate that the galactic supernovae 1054 and 1181 could be attributed to SN 1997D-like events. (orig.)Available from TIB Hannover: RR 4697(1184) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman