ar X iv : a st ro - p h / 97 07 22 9 v 1 2 1 Ju l 1 99 7 Metallicity Dependence of the Cepheid Calibration
نویسندگان
چکیده
The metallicity dependence of the Cepheid period-luminosity (PL) relation has been a controversial issue. The more commonly accepted view is that the PL relation is insensitive to metal abundance, while the period-luminosity-colour relation is fairly sensitive, as indicated by stellar pulsation models 1−4 (see also refs. 5,6). The direct observational evidence is scanty, however. Freedman and Madore 7 have studied Cepheids in three regions having different metallicity in M31 and concluded no statistically significant residual differences in the distance moduli. On the other hand, Gould 8 has claimed that the data of Freedman and Madore are rather indicating a large metallicity dependence ∆µ/∆[Fe/H] = 0.88±0.16, where µ is the distance modulus derived from the Cepheid PL relation. A moderate metal-licity dependence ∆µ/∆[Fe/H] = 0.44 was also concluded in a recent report from EROS photometry for the Magellanic Clouds 9. Recently an accurate measurement of metallicity has been carried out for 23 Galactic Cepheids by Fry and Carney 10 (hereafter FC). This work has given us an opportunity to examine the metallicity dependence of the Cepheid PL relation and its calibrations. The most commonly used calibration of the Galactic Cepheids is probably that of Feast and Walker 11 based on V band photometry and the distance based on the ZAMS fitting to the clusters that contain the Cepheids. Laney and Stobie 12 (hereafter LS) have slightly updated the Feast-Walker distance and also provided a calibration of the Cepheid PL
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