SIMBAD references

Aims. We analysed a sample of SiO-masing late-type stars located in the inner Galaxy with the goal of setting better constraints on their obscuration.
Methods. This reference sample has allowed us to define mathematical relations between their dereddened infrared colours and the observed colours (e.g. K_s-[8], K_s-[24]).
Results. The derived equations define a property (the locus) of these late-type stars. Therefore, they enable us to derive the interstellar extinction. With estimated spectral types, it is possible to decompose the total extinction in the two components (interstellar and envelope extinction).
Conclusions. These relations are useful for classifying extremely obscured late-type stars located in the inner Galaxy. Estimating the two extinction components can be performed on an individual late-type star, independently of its surroundings and even when few mid-infrared measurements are available.