Modern supernova searches in the nearby Universe are discovering large numbers of SNe which have massive star progenitors (Types II, Ib and Ic). The extensive HST image archive within ~20Mpc enables the indvidual bright stellar content of starforming galaxies to be resolved. As massive, evolved stars are the most luminous single objects in a galaxy, the progenitors of core-collapse SNe are often directly detectable on pre-explosion archive images. We have discovered three progenitors of recent type II-Plateau SNe, showing them to be red supergiants of 8-12 solar masses. This is the first direct evidence that red supergiants do indeed produce normal type II explosions. We have set upper mass limits on a further 7 progenitor stars and suggest that faint type II supernovae are unlikely to come from the collapse of very massive stars which form black holes. These discoveries are providing strong constraints on theoretical models of pre-supernova evolution, explosion models and the origin of the supernova types. We request time to continue this successful project and require ACS observations of future SNe which are discovered in galaxies closer than 20Mpc and which have pre-explosion HST archive images available. This will allow the SNe to be precisely positioned on the pre-explosion images. We have set a final goal for this project of determining masses and types, or setting restrictive mass-limits, for 30 supernovae over the remainder of HST's project life.

We will image future nearby supernovae with ACS, using either the HRC or the WFC. Supernovae will only be observed if there is pre-explosion HST imaging in more than one filter available, and if the supernova is a core-collapse, and if it is within approximately 20Mpc. The goal of the programme is to identify the massive star progenitors of supernovae in HST archive images. To do this we need precise differential astrometry between the before and after. The images in this proposal will provide the astrometry of the supernova for comparison with pre-explosion images. This is a ToO programme, in which we cannot specify targets for the Phase II deadline, but will trigger on suitable objects as the Cycle progresses. Generally we can plan well in advance, and not disrupt the HST schedule. 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