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OGLE-ing the Magellanic System: Photometric Metallicity from Fundamental Mode RR Lyrae Stars

Skowron D. M., Soszyński I., Udalski A., Szymański M. K., Pietrukowicz P., Skowron J., Poleski J., Wyrzykowski Ł., Ulaczyk K., Kozłowski S., Mróz P., Pawlak M.

Acta Astronomica

2016

Vol. 66, No. 3

269--292

In an era of extensive photometric observations, the catalogs of RR Lyr type variable stars number tens of thousands of objects. The relation between the iron abundance [Fe/H] and the Fourier parameters of the stars light curve allows us to investigate mean metallicities and metallicity gradients in various stellar environments, independently of time-consuming spectroscopic observations. In this paper we use almost 6500 V- and I-band light curves of fundamental mode RR Lyr stars from the OGLE-IV survey to provide a relation between the V- and I-band phase parameter ϕ31 used to estimate [Fe/H]. The relation depends on metallicity, which limits its applicability. We apply this relation to metallicity formulae developed for the Johnson V- and the Kepler Kp-band to obtain the relation between [Fe/H] and ϕ31 for the I-band photometry. Last, we apply the new relation of Nemec to the OGLE-IV fundamental mode RR Lyr stars data and construct a metallicity map of the Magellanic Clouds. Median [Fe/H] is -1.39±0.44 dex for the LMC and -1.77±0.48 dex for the SMC, on the Jurcsik metallicity scale. We also find a metallicity gradient within the LMC with a slope of -0.029±0.002 dex/kpc in the inner 5 kpc and -0.030±0.003 dex/kpc beyond 8 kpc, and no gradient in-between (-0.019±0.002 dex/kpc integrally). We do not observe a metallicity gradient in the SMC, although we show that the metal-rich RRab stars are more concentrated toward the SMC center than the metal-poor.

Fourier Analysis of Hipparcos Photometry of Cepheid Variables

Zakrzewski B., Ogłoza W., Moskalik P.

Acta Astronomica

2000

Vol. 50, No. 3

387--397

Fourier parameters have been computed for 240 field Cepheids observed by the Hipparcos satellite. We have identified three new Population I overtone Cepheids: V411 Lac, V898 Cen and V572 Aql. We have compared Fourier progressions of Population I and Population II Cepheids. The possibility of using Fourier parameters to distinguish between the two types is discussed.