Context : Increasing the statistics of evolved massive stars in the Local Group enables investigating their evolution at different metallicities .
During the late stages of stellar evolution , the physics of some phenomena , such as episodic and systematic mass loss , are not well constrained .
For example , the physical properties of red supergiants ( RSGs ) in different metallicity regimes remain poorly understood .
Thus , we initiated a systematic study of RSGs in dwarf irregular galaxies ( dIrrs ) in the Local Group .

Aims : We aim to derive the fundamental physical parameters of RSGs and characterize the RSG population in nearby dIrrs .

Methods : The target selection is based on 3.6 \mu m and 4.5 \mu m photometry from archival Spitzer Space Telescope images of nearby galaxies .
We selected 46 targets in the dIrrs IC 10 , IC 1613 , Sextans B , and the Wolf-Lundmark-Melotte ( WLM ) galaxy that we observed with the GTC–OSIRIS and VLT–FORS2 instruments .
We used several photometric techniques together with a spectral energy distribution analysis to derive the luminosities and effective temperatures of known and newly discovered RSGs .

Results : We identified and spectroscopically confirmed 4 new RSGs , 5 previously known RSGs , and 5 massive asymptotic giant branch ( AGB ) stars .
We added known objects from previous observations .
In total , we present spectral classification and fundamental physical parameters of 25 late-type massive stars in the following dIrrs : Sextans A , Sextans B , IC 10 , IC 1613 , Pegasus , Phoenix , and WLM .
This includes 17 RSGs and 8 AGB stars that have been identified here and previously .

Conclusions : Based on our observational results and PARSEC evolutionary models , we draw the following conclusions : ( i ) a trend to higher minimum effective temperatures at lower metallicities and ( ii ) the maximum luminosity of RSGs appears to be constant at \log ( L / L _ { \sun } ) \approx 5.5 , independent of the metallicity of the host environment ( up to \mathrm { [ Fe / H ] } \approx -1 dex ) .