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Metallicity Estimates for Double-Mode Cepheids from Photometry

Szilàdi K., Vinkò J., Szabados L.

Acta Astronomica

2018

Vol. 68, No. 2

111--123

We investigate the effect of different metallicities on the light curve shape of classical double-mode (beat) Cepheids pulsating in the fundamental and first overtone modes by correlating the light curve Fourier parameters with [Fe/H] ratios. We combine data of known Galactic beat Cepheids with those from both Magellanic Clouds assembled by the OGLE-III and OGLE-IV surveys. The [Fe/H] values for the Galactic sample are based on recent high-resolution spectroscopy. For the Magellanic sample we apply the metallicity-period-period ratio relationship to estimate individual [Fe/H] values. We confirm that the metallicity is most strongly correlated with the amplitude of the light curve and the amplitude ratio of the first and second harmonics (R21), similar to single-mode classical Cepheids found by Klagyivik. We also show that the metallicity is less correlated with φ31 parameter in our sample, as compared with the case of the RR Lyr type variables. We derive empirical formulae that can be used to estimate the [Fe/H] of classical Cepheids that extends well below the metallicity of the Milky Way disk, down to the lower metallicities of the Magellanic Clouds.