As stars approach the end of their life cycles, do they age gracefully as smooth round orbs or do they vibrate so strongly that their surfaces become distorted? Do they break out in spots across their surfaces? Do they puff out their atmospheres with a thin halo of gas? The combined power of 3 interferometers is being brought to bear on these basic questions about the end stage of stellar life, in particular for the Mira variable stars. This research group is imaging the surfaces and the innermost silicon oxide maser and dust shells of Mira stars, at different wavelengths using the 3 interferometers. There already is strong evidence at the three facilities, the Infrared Optical Telescope Array, the Very Long Baseline Array, and the Infrared Spatial Interferometer array, that a subset of Miras exhibits measurable asymmetries on their surfaces and inner shells. This coordinated effort is directly investigating the space and time connection between asymmetries on the stellar surfaces and in the masers and dust shells. The work is focused on this subset of 11 Miras, mapping the structure of these giant stars in the near infrared, radio, and mid-infrared to learn to what extent asymmetries are correlated. They are measuring the diameters and asymmetry of 5 particular Miras in the near infrared continuum and absorption bands in order to learn about vertical photospheric structure, and horizontal variations. These observations are leading to an improved physical picture of the ejection dynamics of these long-period variable stars. The images will be the first of their kind in terms of angular resolution, spectral coverage and sensitivity.
BROADER IMPACTS. This research is filling out this as-yet little explored part of the stellar evolution picture, and so helping to explain how stars eventually start recycling their mass into space. Through ongoing public outreach activities, they are spreading this knowledge in public lectures and teacher training workshops. Scientific partnerships flow naturally from this line of research, as many colleagues in astrophysics are deeply interested in these issues. The larger benefit to society will come from what we learn about old stars and what we can relay to the public, thereby enhancing people's understanding of the universe in which we live, and demonstrating that one of the benefits of pure scientific research can be simply pure intellectual enjoyment.
