Imaging Convective Patterns On AGB Stars

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Even in the absence of distortions caused by our atmosphere, our ability to the resolve spatial structure of distant objects is limited by the diameter of telescope mirrors. Optical Interferometers, such as Georgia State University's Center for High Angular Resolution Astronomy (CHARA), get around this limitation by combining the signals received by smaller telescopes placed a long distance apart. We are now able to measure the sizes and shapes of bright stars, and we are beginning to be able to image their surfaces. This team will study the brightness variations on the surface of giant stars, which is caused by convection just beneath the surfaces. In turn, this will enable a better understanding of how the "winds" from these stars replenishes and enriches the interstellar medium, from which future generations of stars (and planets) are formed. This project will be used to train Georgia State University's undergraduate students in astronomy, optics, and computer science. The goal of this proposal is to image the surfaces of a group of chemically-diverse asymptotic giant branch (AGB) stars via long baseline near-IR interferometry using CHARA. The investigators will monitor the lifetime, size, and variability of the AGB convection patterns over the three-year duration of the project. Their maps of the surface effective temperatures will then be compared to predictions made by state-of-the-art 3D radiative-hydrodynamics models to determine regions of high mass-loss and to determine how that mass is distributed back into the interstellar medium via stellar winds. Imaging different types of AGBs with sub-milliarcsecond resolution will help quantify the roles of convection, pulsation, multiplicity and magnetism in the variability and mass-loss processes. The PI will also conduct workshops designed to help broaden the community of astronomers capable of obtaining and analyzing interferometric observations. They will also develop open source codes to produce images of a wide variety of stars from interferometric data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.