Investigation of mid-infrared long-term variability of dusty AGB stars using multi-epoch scan data of AKARI and WISE

Abstract

Abstract Asymptotic giant branch (AGB) stars are one of the main sources of dust in the Universe. They form and supply dust triggered by stellar pulsations, but the details of the mechanism are still unknown. Among all AGB stars, dusty AGB stars are the most important in terms of dust supply because they contain the star with a high mass-loss rate. To investigate the relationship between the pulsation and the dust supply for such dusty AGB stars, long-term mid-infrared monitoring is necessary. In this study, we combine data from a infrared astronomical satellites AKARI and WISE to generate mid-infrared long-term observation data. This collected data enables us to investigate the variability of dusty AGB stars with a variability period of more than several hundred days (>250 d). Furthermore, we determine the mid-infrared variability amplitudes of 169 O-rich AGB stars and 28 OH/IR stars in our Galaxy, as well as data at other wavelengths. This study is the largest study on mid-infrared variability. Additionally, we discover a positive correlation between the variability amplitude A18μm in the 18μm band and the $\mathit {W3}-\mathit {W4}$ infrared color which is the measure of the dust supply. Also, we find that this relationship is independent of the variability period and mode. Finally, we calculate the radiative transfer of circumstellar dust from AGB stars. The result of our calculations showed that $A_{18\mu \rm {m}}$ is strongly affected by the luminosity change ratio of the central star. These experimental results imply that the luminosity change ratio has a strong influence on the dust supply of AGB star.