Near Infrared Angular Diameters of a few AGB variables by Lunar Occultations

TL;DR

This study reports near-infrared lunar occultation measurements of angular diameters for several AGB variables, introduces a method to predict diameters from color indices, and examines mass-loss effects on these measurements.

Contribution

First-time angular diameter measurements for two Miras and one SRV in the near-infrared K-band, and a new method to estimate diameters from (V-K) color.

Findings

Measured diameters of some AGB variables are significantly affected by mass loss.

A new predictive method for angular diameters based on (V-K) color is discussed.

Mass loss can cause up to 40% enhancement in observed angular diameters.

Abstract

The uniform disk (UD) angular diameter measurements of two oxygen-rich Mira variables (AW Aur and BS Aur) and three semiregular (SRb) variables (GP Tau, RS Cap, RT Cap), in near Infrared K-band (2.2 micron) by lunar occultation observations are reported. UD angular diameters of the two Miras and one SRV are first time measurements. 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 enhanced by nearly 40% compared to its expected value, possibly due to mass loss effects leading to formation of a circumstellar shell.