Discovery of candidate luminous blue variables in M31

Luminous blue variables (LBVs) constitute a short-lived, eruptive phase in the evolution of some of the most massive stars. Only a handful have yet be en identified in the Galaxy and in each of the nearby galaxies; there are f our known LBVs in M31. We have found an efficient method to identify candid ate LBV stars in nearby galaxies. The candidates are identified in a pair o f deep, continuum-subtracted narrowband H alpha and [S II] images as object s with extremely low [S II] to H alpha ratios, and with coincident stellar objects in continuum images. Five of the most promising new candidates iden tified by these criteria in the northeastern half of M31 were subsequently confirmed by optical spectroscopy to show spectra similar to the previously identified M31 LBV, HS var 15. These five candidates also have much in com mon with B[e] stars, of which none were known to exist in M31. They are bri ght Ha sources, (120 L. < L-H alpha < 1300 L.) with no detectable [S II] em ission, large H alpha equivalent widths (-60 to -400 Angstrom), and broad w ings on the H alpha profiles (FWZI = 1200-2000 km s(-1)). Most candidates h ave Fe II emission. We discuss the environments of the candidates and find that many objects are likely older than several million years because they tend not to be located inside bright H II regions. We predict, based on the current results, that at least 20-25 LBV/B[e] candidates may be present in M31.