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Paper: Galactic Chemical Enrichment Ratio ΔY/ΔZ from a Sample of Nearby K Dwarfs
Volume: 374, From Stars to Galaxies: Building the Pieces to Build Up the Universe
Page: 71
Authors: Casagrande, L.
Abstract: We compare a large sample of nearby K dwarfs with a set of theoretical isochrones computed with different helium and metallicity content, with the main aim to determine the helium-to-metal enrichment ratio ΔYZ in the Solar Neighbourhood. For all stars we have derived homogeneous fundamental stellar parameters which allow us to study the broadening of the Low Main Sequence in the theoretical HR diagram, where the effects of helium and ΔYZ are more prominent. Surprisingly, the offset between the metal rich and metal poor Main Sequence is less than expected, so that to fit metal poor dwarfs, stellar models with anomalously low helium content must be used. We have investigated various effects that could help in solving such a problem. Our theoretical isochrones are then checked against a congruous set of Main Sequence binaries to discuss and validate their applicability range. The helium-to-metal enrichment ratio is found to be ΔYZ = 2.0 1.0 around solar metallicity whereas open problems still remain at the lowest metallicities.
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