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Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids 1

By David Yong, Bruce W. Carney, Maria Luísa, Teixera Almeida and Brian L. Pohl


We present metallicities, [Fe/H], and elemental abundance ratios, [X/Fe], for a sample of 24 Cepheids in the outer Galactic disk based on high-resolution echelle spectra. The sample have Galactocentric distances covering 12 ≤ RGC (kpc) ≤ 17.2 making them the most distant Galactic Cepheids upon which detailed abundance analyses have been performed. We find sub-solar ratios of [Fe/H] and overabundances of [α/Fe], [La/Fe], and [Eu/Fe] in the program stars. All abundance ratios exhibit a dispersion that exceeds the measurement uncertainties. As seen in our previous studies of old open clusters and field giants, enhanced ratios of [α/Fe] and [Eu/Fe] reveal that recent star formation has taken place in the outer disk with Type II supernovae preferentially contributing ejecta to the ISM and with Type Ia supernovae playing only a minor role. The enhancements for La suggest that AGB stars have contributed to the chemical evolution of the outer Galactic disk. Some of the young Cepheids are more metal-poor than the older open cluster

Year: 2005
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