5 Conclusions and future work

We have looked for candidate light echoes around 64 supernovae of all Types in 38 galaxies. From this ground-based photometric data we notice optical emission at the SN nominal positions. The color distribution of these patches is broad, and generally consistent with stellar population colors, possibly with some reddening. However there are in addition patches with both unusually red and unusually blue colors. We expect light echoes to be blue, and while none of the objects are quite as blue in V-R as the known light echo of SN1991T, there are features that are unusually blue and we identify these as candidate echoes for follow-on space and ground observations.

We also made reference to archival WFPC-2/HST observations of fourteen SN fields. These showed that some of the patches resolve into multiple point sources, while others do not. The absence of multi-color information within the HST data precludes us from narrowing down our candidate list further, since at WFC resolution we do not expect the SN remnants to show significant spatial extent. As discussed in the text and in Sparks (1994) only polarimetric observations of a field many arcsec in extent around the SN position can succeed in determining whether (or not) there is an extended structure. This is the basis for future observations using the Advanced Camera on the Hubble Space Telescope.

From the color/color plots we notice that indeed different SN Types are characterized by different environments. SNe Ia tend to be redder than (B-V)=0-0.1 and (V-R)=0-0.1, while Type Ib/II are bluer than these values. This distribution seems to reflect the distribution of various SN Types in different regions of the parent galaxies and in different galaxies as well. SNe II/Ib likely derive from massive progenitors in spiral galaxies and thus are associated to star-formation regions where a strong H$\alpha$ emission is present (Van Dyk et al. 1996 and references therein). Type Ia SNe, instead, possibly derive from a wider variety of stellar environments (as they are observed both in elliptical and spiral galaxies).

Acknowledgements

F.R.B. would like to thank Angela Bragaglia, David Branch, Enrico Cappellaro, Massimo Della Valle, Boris Dirsch, Claus Leitherer, Arturo Manchado, Ulisse Munari and Elena Pian for useful discussions and encouragement.