AGB region of the H-R diagram. The lines display solar metallicity evolutionary tracks from Marigo et al. (2013): gray lines mark the regions of Oxygen-rich stars with C/O < 1.0; yellow lines denote the region of C-rich stars with , while black lines mark stars with C/O > 1.5. The numbers indicate the mass values at the beginning of the thermal pulsing (TP)-AGB. For better visibility, the track with 2 M_⊙ is plotted with a dotted line. Different symbols and colors refer to the luminosity and effective temperature, estimated through the comparison in this work of the models with spectro-photometric-interferometric-observations. A typical error-size bar is shown in the lower side of the figure.