AKARI color useful for classifying chemical types of Miras

Abstract

The AKARI/IRC color combining the S9W and L18W bands is useful for distinguishing between oxygen-rich and carbon-rich circumstellar dust. Ishihara and collaborators found in 2011 that this color, used together with the near-IR color J-Ks, can be used to classify two groups of dust-enshrouded stars with different chemistry. They investigated the distributions of such dusty AGB stars in the Galaxy and found that those with oxygen-rich dust are more centrally concentrated. While this is consistent with previous studies, the map in Ishihara et al. shows that carbon-rich stars are also present in the Galactic bulge for which almost no carbon-rich stars were reported before. Here we focus on Mira variables whose distances can be well constrained based on the period-luminosity relation. Among some candidates of carbon-rich Miras selected by the AKARI color, we confirmed at least four carbon-rich Miras within the bulge with their optical spectra. This gives a new insight into the complicated nature of stellar populations in the bulge.