The intrinsic dispersion of elemental abundance ratios in nearby metal-poor halo stars

Original Abstract

Differential abundances of C, O, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, and Zr were determined from high signal-to-noise VLT/UVES spectra for 25 turnoff stars with -2.4 < [Fe/H] < -1.3. Effective temperatures were obtained from profiles of the H_beta line and surface gravities via Gaia parallaxes. The analysis of the spectra were based on 1D model atmospheres assuming LTE, but 3D non-LTE corrections were applied for several elements. The dispersion in linear fits to the [X/Fe]-[Fe/H] relations is around a factor of two smaller than found in previous studies. After corrections for measurement errors, the 1-sigma intrinsic dispersion of [X/Fe] at a given metallicity is 0.09 dex for Y and Zr, 0.05-0.07 dex for C, O, and Al, 0.03-0.05 dex for Mg, Ca, Sc, Ti, V, Mn, and Zn, and <0.03 dex for Cr, Co, and Ni. Strong correlations between the residuals in the [X/Fe]-[Fe/H] fits are found for the alpha-capture elements Mg, Al, Ca, Sc, and Ti and between the residuals for Y and Zr. Correlations of the residuals in the [X/Fe]-[Fe/H] fits with effective temperature can be explained as due to differential atomic diffusion between elements, but its contribution to the scatter of [X/Fe] is of minor importance. Probably, both stochastic effects in sampling the IMF of CCSNe and differences in the TypeIa to CCSNe enrichment ratio between star-forming regions need to be considered in order to explain the intrinsic dispersion of [X/Fe].