NEAR-INFRARED OBSERVATIONS OF SiO MASER-EMITTING ASYMPTOTIC GIANT BRANCH (AGB) STARS

Abstract

Near-infrared (NIR) monitoring observations of asymptotic giant branch stars exciting bright SiO masers have been made with the 1 m telescope of Kagoshima University. In order to investigate the properties of these stars and their envelopes, we combined our NIR photometric data with mid- and far-infrared flux data obtained by the IRAS satellite, SiO maser flux data provided by the Nobeyama Radio Observatory, visual magnitude data provided by the AAVSO, and the reported data on the expansion velocities of the circumstellar envelopes. The absolute magnitudes at the K -band and the distances are estimated using the period–luminosity relation of Mira variables determined by Feast et al. Then, mass-loss rates and isotropic luminosities of an SiO maser are estimated. The mass-loss rates range from approximately 10 −8    to over 10 −5   . We found that the NIR pulsation amplitudes are correlated with the pulsation periods and the observed wavelengths. We also found correlations of the isotropic luminosities of SiO masers with the mass-loss rates and absolute magnitudes at the K -band. These results will help us to understand the pumping mechanism of SiO masers. We measured, for the first time, the periods and/or NIR magnitudes of TX Cam, BW Cam, IRAS 06297+4045, IRAS 18387–0423, and RT Cep.