On the Existence of Stable Stars in the Cepheid Instability Strip

Forty-eight stars with spectral types near GO Ib have been examined for light variability. Five stars, HD 191010, 239994, 84441, 213482, and 214847, are suspected of being variable by about mag. The remaining forty-three stars appear to be stable to within a few hundredths of a magnitude. HD 194012, with a published spectral type of F8 Ib, was found in fact to be an F7 V star. Intrinsic colors for many of the nonvariable stars were assembled from published B VRI photometry. Absolute magnitudes for a number of them were obtained from cluster membership, K-line widths, etc. Most of these stars appear to lie within the Cepheid instability strip on the H-R diagram; and in a few favorable cases for which the absolute magnitude seems well determined by several independent means, this conclusion appears almost certain.