We present adaptive optics imaging of the core collapse supernova ( SN ) 2009md , which we use together with archival Hubble Space Telescope data to identify a coincident progenitor candidate .
We find the progenitor to have an absolute magnitude of V = -4.63 ^ { +0.3 } _ { -0.4 } mag and a colour of V - I = 2.29 ^ { +0.25 } _ { -0.39 } mag , corresponding to a progenitor luminosity of log L /L _ { \odot } \sim 4.54 \pm 0.19 dex .
Using the stellar evolution code STARS , we find this to be consistent with a red supergiant progenitor with M = 8.5 _ { -1.5 } ^ { +6.5 } M _ { \odot } .
The photometric and spectroscopic evolution of SN 2009md is similar to that of the class of sub-luminous Type IIP SNe ; in this paper we compare the evolution of SN 2009md primarily to that of the sub-luminous SN 2005cs .
We estimate the mass of ^ { 56 } Ni ejected in the explosion to be ( 5.4 \pm 1.3 ) \times 10 ^ { -3 } M _ { \odot } Â from the luminosity on the radioactive tail , which is in agreement with the low ^ { 56 } Ni masses estimated for other sub-luminous Type IIP SNe .
From the lightcurve and spectra , we show the SN explosion had a lower energy and ejecta mass than the normal Type IIP SN 1999em .
We discuss problems with stellar evolutionary models , and the discrepancy between low observed progenitor luminosities ( log L /L _ { \odot } \sim 4.3 - 5 dex ) and model luminosities after the second-dredge-up for stars in this mass range , and consider an enhanced carbon burning rate as a possible solution .
In conclusion , SN 2009md is a faint SN arising from the collapse of a progenitor close to the lower mass limit for core-collapse .
This is now the third discovery of a low mass progenitor star producing a low energy explosion and low ^ { 56 } Ni ejected mass , which indicates that such events arise from the lowest end of the mass range that produces a core-collapse supernova ( 7 - 8 M _ { \odot } ) .