Combined $BVRI$ and H$\alpha$ / [SII] Observations of M31 SNRs
Session 2 -- Planetary Nebula and Supernova Remnants
Display presentation, Monday, 9:20-6:30, Pauley Room

## [2.19] Combined $BVRI$ and H$\alpha$ / [SII] Observations of M31 SNRs

E.~Magnier, W.H.G.~Lewin (MIT), S.~Prins, J.~van~Paradijs (UVA), G.~Hasinger, W.~Pietsch, R.~Supper, J.~Tr\"{u}mper (MPE)

We present results of combined $BVRI$, H$\alpha$, and [SII] CCD observations of emission-line regions in M31. These regions contain complex stellar associations and extensive H$\alpha$ emission. Much of the H$\alpha$ emission is due to photo-ionization (H{\scriptsize II} regions), but supernova remnants (SNRs) are also mixed in with the emission regions. Several groups (Blair et. al. 1981, D'Odorico et. al. 1980) have identified SNRs based on the [SII] to H$\alpha$ ratio. While objects with a relatively high value of [SII]~/~H$\alpha$ are very likely to be SNRs, this ratio is not very high for many SNRs. Such SNRs are therefore easily missed in optical searches for extragalactic SNRs. We present a different, complementary test for SNRs based on a comparison of the H$\alpha$ flux and the presence or absence of hot, ionizing stars. Our combined $BVRI$, H$\alpha$, [SII] data has revealed $\sim200$ objects which are candidate SNRs throughout M31 based on this test.