Metallicity-dependent mixing length in the evolutionary model from red supergiant stars in IC 1613

Abstract

We investigate near-infrared spectroscopic data of red supergiant stars (RSGs) in the irregular dwarf galaxy IC 1613 using the MMIRS at the MMT telescope. The effective temperatures ( T _eff ) and metallicities of 14 RSGs are obtained by synthetic spectral fitting to the observed spectra. We find a weak bimodal distribution of the RSG metallicity centered on the [Fe/H]=-0.65. We also find that the average T _eff of the RSGs in IC 1613 is higher by about 250 K than that of the SMC. By comparing stellar evolutionary tracks with the RSG in the HR diagram, the models with α _MLT = 2.2–2.4 H _p can best reproduce the effective temperatures of the RSGs in IC 1613. This result supports our previous study that the mixing length increases with increasing metallicity to explain the RSG temperature.