Infrared two-colour diagrams for AGB stars using AKARI, MSX, IRAS and near-infrared data




Using a revised version of the catalogue of asymptotic giant branch (AGB) stars by Suh & Kwon, we present various infrared two-colour diagrams (2CDs) for 3003 O-rich, 1168 C-rich, 362 S-type and 35 silicate carbon stars in our Galaxy. For each object in the new catalogue, we cross-identify the AKARI, Midcourse Space Experiment (MSX) and Two-Micron All-Sky Survey (2MASS) counterparts by finding the nearest object from the position information in the Infrared Astronomical Satellite (IRAS) Point Source Catalog (PSC). For the large sample of AGB stars, we present infrared two-colour diagrams using IRAS (PSC), AKARI (PSC and bright-source catalogue (BSC)), MSX (PSC) and near-infrared (K and L bands, including 2MASS data in the KS band) data for different classes of AGB stars based on the chemistry of the dust shell and/or the central star. The infrared two-colour diagrams (2CDs) of AGB stars can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. On the 2CDs, we plot tracks of the theoretical radiative transfer model results with increasing dust-shell optical depths. Comparing the observations with the theoretical models on the new 2CDs, we find that the basic model tracks roughly coincide with the densely populated observed points. Generally, we can explain the observations of O-rich and C-rich AGB stars on the various 2CDs with theoretical models using dust opacity functions of amorphous silicate, amorphous carbon, SiC and corundum. For O-rich AGB stars, we find that the models using corundum as well as silicate can improve the fit to the observations.