A discussion of the Cepheid amplitude behaviour in the instability strip

An analysis is presented which seeks to reveal the possible causes for discrepancy in the results on the dependence of Cepheid amplitudes on star positions in the instability strip noted by different investigators.A comparison of the data used in two of these investigations—that of Yakimova (1970) and that of Sandage and Tammann (1971)—shows that it is most unlikely to be able to explain completely the conflicting results obtained in these studies. But if we analyse the data of Sandage and Tammann following the approach of Yakimova — namely, by considering the Cepheids in only one stellar system and taking into account the stellar colours in maximum light — we obtain Yakimova's result: the light amplitude is the larger, the nearer to the low temperature edge of the instability strip a Cepheid is. Therefore, it appears that differences between the various approaches contribute greatly to the different results of Sandage and Tammann and Yakimova (and the other investigators).