Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-09-22
Mem.Soc.Ast.It.77:239-244,2006
Astronomy and Astrophysics
Astrophysics
6 pages, to appear in the proceedings of the "Stellar Pulsation and Evolution" conference, Monte Porzio Catone, June 2005
Scientific paper
{Results from a long-term observational project called the Araucaria Project are presented. Based on Wide Field optical monitoring of 8 nearby galaxies, covering a large range of metallicities, more than 500 Cepheids and a few hundred Blue Supergiant candidates were identified. From the analysis of Cepheid P-L relations of outstanding quality derived from our data we conclude that the slope of these relations in the I band and Wesenheit index are not dependent on metallicity. Comparing the I-band magnitudes of Cepheids of a period of ten days, as computed from our P-L relations, to the I-band magnitudes of the tip of the RGB, which is widely believed to be independent of population effects, we cannot see any obvious dependence of the zero point of the I-band P-L relation on metallicity. A preliminary analysis of IR follow-up observations of sub-samples of the identified Cepheids in various galaxies of the project show that the distances obtained from these data are systematically shorter by about of 0.1 mag than those derived from the optical photometry. It is likely that this effect can be attributed to the internal reddening in the program galaxies.
Gieren Wolfgang
Pietrzynski Grzegorz
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