A large fraction of core-collapse supernovae ( CCSNe ) , 30-50 % , are expected to originate from the low-mass end of progenitors with M _ { ZAMS } = 8 - 12 M _ { \odot } .
However , degeneracy effects make stellar evolution modelling of such stars challenging , and few predictions for their supernova light curves and spectra have been presented .
Here we calculate synthetic nebular spectra of a 9 M _ { \odot } Fe CCSN model exploded with the neutrino mechanism .
The model predicts emission lines with FWHM \sim 1000 km s ^ { -1 } , including signatures from each deep layer in the metal core .
We compare this model to observations of the three subluminous IIP SNe with published nebular spectra ; SN 1997D , SN 2005cs , and SN 2008bk .
The prediction of both line profiles and luminosities are in good agreement with SN 1997D and SN 2008bk .
The close fit of a model with no tuning parameters provides strong evidence for an association of these objects with low-mass Fe CCSNe .
For SN 2005cs , the interpretation is less clear , as the observational coverage ended before key diagnostic lines from the core had emerged .
We perform a parameterised study of the amount of explosively made stable nickel , and find that none of these three SNe show the high ^ { 58 } Ni/ ^ { 56 } Ni ratio predicted by current models of electron capture SNe ( ECSNe ) and ECSN-like explosions .
Combined with clear detection of lines from O and He shell material , these SNe rather originate from Fe core progenitors .
We argue that the outcome of self-consistent explosion simulations of low-mass stars , which gives fits to many key observables , strongly suggests that the class of subluminous Type IIP SNe is the observational counterpart of the lowest mass CCSNe .