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Appendix A: Error estimates

We refer the reader to the analogous Appendices in Carretta et al. (2009a,b) for a detailed discussion of the procedure adopted for error estimates. In the following, we only provide the main tables of sensitivities of abundance ratios to the adopted errors in the atmospheric parameters and EWs and the final estimates of internal and systematic errors for all species analysed from UVES and GIRAFFE spectra of stars in NGC 362.

The sensitivities of derived abundances on the adopted atmospheric parameters were obtained by repeating our abundance analysis by changing only one atmospheric parameter each time for all stars in NGC 362 and by taking the average value of the slope change vs. abundance. This exercise was done separately for both UVES and GIRAFFE spectra.

We notice that the values usually adopted (determined from the scatter of abundances from individual lines) are overestimated when estimating the contribution to internal errors due to EWs and v_t, because regularities in the data are not considered.

These regularities are due to uncertainties in the gf-values, unrecognised blends with adjacent lines, inappropriate positioning of the continuum, etc. They show up in uniform deviations of individual lines from average abundances for each star. By averaging over all stars the residuals of abundances derived from individual lines with respect to the average value for each star, we estimated that some 36% of the total variance in the Fe abundances from individual lines is due to systematic offsets between different lines, which repeat from star-to-star. For about 30% of the line, these offsets have trends with temperature significant at about 2σ level. However, we found that the additional fraction of variance that can be explained by these trends is very small, and we can neglect it. We conclude that the errors in EWs and v_t should be multiplied by 0.8 when considering star-to-star variations (internal errors, according to our denomination).

The amount of the variations in the atmospheric parameters is shown in the first line of the headers in Tables A.1 and A.2, whereas the resulting response in abundance changes of all elements (the sensitivities) are shown in columns from 3 to 6 in these tables.

© ESO, 2013