Chemical abundances of red supergiants I.

Finally, we determine the abundance ratios ([X/Fe] for element X) also through the fitting of individual lines. We determined [X/Fe] of ten elements (NaI, MgI, AlI, SiI, KI, CaI, TiI, CrI, NiI, and YII). We estimated the relative precision in the derived abundances to be 0.04-0.12dex for elements with more than two lines analyzed (e.g., FeI and MgI) and up to 0.18dex for the other elements (e.g., YII).

We compared the resultant abundances of RSGs with the well-established abundances of another type of young stars, Cepheids, to evaluate the potential systematic bias in our abundance measurements, assuming that the young stars (i.e., both RSGs and Cepheids) in the solar neighborhood have common chemical abundances. Consequently, we found that the determined RSG abundances are well consistent with Cepheids within <~0.1dex for some elements (notably, [Fe/H] and [Mg/Fe]).

In other words, the bias in the abundance determination for these elements would be small. In contrast, the consistency is worse for some other elements (e.g., [Si/Fe] and [Y/Fe]). Nevertheless, the dispersion of the chemical abundances among our target RSGs was comparable with the individual statistical errors of the abundances.

Hence, the procedure would be useful for evaluating the relative difference in chemical abundances among RSGs.