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Published online by Cambridge University Press: 03 August 2017
From the m12 – m25vs. spectral type diagram (see for example: Habing, 1987, Figure 5), it can be seen that there are no early M giant stars with m12 – m25 > 0.7. On the other hand all early M stars with m12 – m25 > 0.7 are M supergiants. These early type M supergiants have typically infrared excesses at 12 μm in the range of 20 to 170 times higher than their photosperic fluxes.