Angular Size Measurements of Mira Variable Stars at 2.2 Microns. II.

Abstract

We present angular size measurements of 22 oxygen-rich Mira variable stars. These data are part of a long term observational program using the Infrared Optical Telescope Array (IOTA) to characterize the observable behavior of these stars. Complementing the infrared angular size measurements, values for variable star phase, spectral type, bolometric flux and distance were established for stars in the sample; flux and distance led to values for effective temperature, and linear radius, respectively. Additionally, values for the K-[12] color excess were established for these stars, which is indicative of dusty mass loss. Stars with higher color excess are shown to be systematically 120 solar radii larger than their low color excess counterparts, regardless of period. This analysis appears to present a solution to a long-standing question presented by the evidence that some Mira angular diameters are indicative of first overtone pulsation, while other diameters are more consistent with fundamental pulsation. A simple examination of the resultant sizes of these stars in the context of pulsation mode is consistent with at least some of these objects pulsating in the fundamental mode.