SIMBAD references

The problem of the metallicity sensitivity of the cepheid period-luminosity relations in various spectral regions is reinvestigated following claims by Freedman & Madore (1990) that theoretical predictions (Stothers 1988) and observational evidence are grossly at variance. The effects of metallicity on cepheid colours and magnitudes, as derived from evolutionary calculations and theoretical supergiant atmospheres, are shown to be moderate though by no means negligible. Applied to existing BVRI data for cepheids in three of Baade's fields in M 31 these theoretical abundance corrections turn out to be compatible with the observations and to yield a M 31 modulus 0.mag 14 further than found by FM in excellent agreement with Gould (1994). The above-mentioned disagreement between theory and observations is traced back to the incorrect use of Stothers' results.