Influence of the convective mixing-length parameter α on the chemical abundances in the case of metal-poor giant HD 122563

Abstract

One-dimensional (1D) model atmospheres are still the most commonly used tool for the determination of stellar chemical composition. Convection in the model is usually treated by mixing-length theory (MLT). The mixing-length parameter α is generally calibrated from the Sun and applied to all other stars. The metal-poor giant, HD 122563, is an important benchmark star to test stellar atmosphere and interior physics. We investigate the influence of the convection mixing-length parameter α on the determination of chemical abundances of Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Sr, Y, Zr and Ba in the case of HD 122563, taking advantage of a high resolution and high signal-to-noise ratio HARPS spectrum. The abundance discrepancies Δ[X/H] that occur due to α variation rarely exceed 0.05 dex and most are less than 0.03 dex. We calculate the discrepancy Δ[X/H] using a line-by-line differential analysis. The abundance discrepancies do not have direct relation with either line strength or the excitation potential. For 1D stellar atmospheric analysis of HD 122563, the accuracy of abundance determination does not strongly depend on the choice of mixing-length parameter α (causing average discrepancies of < 0.03 dex), while the uncertainties in the effective temperature and surface gravity play a more important role.