Spectroscopic and Photometric Properties of Late-type BIS Catalogue Sources

We performed slit spectroscopy to establish a firm spectral classification, and optical photometry for variability check in a subsample of 88/276 stars of the Byurakan Infrared Star (BIS) catalog. We collected also literature data from optical monitoring projects (ROTSE, CSS) and infrared satellites (IRAS, AKARI, WISE). We explored several color-color diagrams as tools for disentangling Carbon stars from Oxigen-rich AGB stars and to check for correlations with the variability type. The spectra showed that 4 out of 84 stars are N carbon stars in the Asymptotic Giant Branch (AGB), the others being M-type stars. No Main Sequence stars were found. Thirty stars are not variable, 46 are irregular or semi-regular variables, only 5 are Mira variable stars. The color color plots involving the WISE colors are the best to characterize the variability behavior and to distinguish the carbon stars from the other stars of the sample. The bluer stars were found to be generally not variable, but with some exceptions, and Mira stars occupy a limited region in the w1-w2 vs w2-w3 plane.