Near-infrared angular diameters of a few asymptotic giant branch variables by lunar occultations

The uniform disc (UD) angular diameter measurements of two oxygen-rich Mira variables (AW Aur and BS Aur) and three semiregular (SRb) variables (SRVs; GP Tau, RS Cap and RT Cap) in near-infrared K band (2.2 μm) by lunar occultation observations are reported. UD angular diameters of the two Miras and one SRV are measured for the first time. In addition a method of predicting angular diameters from (V − K) colour is discussed and applied to the five sources. The effect of mass loss enhancing measured K-band diameters is examined for Miras using (K − [12]) colour excess as an index. In our sample the measured angular diameter of one of the Miras (BS Aur) is found to be enhanced by nearly 40 per cent compared to its expected value, possibly due to mass-loss effects leading to formation of a circumstellar shell.