High-resolution observational constraints on the astrophysics of near-circumstellar AGB environments

点击翻译按钮获取中文摘要

AST-0507473Athol KemballUniversity of Illinois at Urbana-ChampaignHigh-resolution observational constraints on the astrophysics of nearcircumstellarAGB environmentsABSTRACTRecent instrumental advances on the Very Long Baseline Array, combined with new techniques formillimeter-wavelength polarimetry over the past decade, have opened a science window on thenear-circumstellar environment of evolved stars unmatched by any contemporary telescope. Thetechnique employed here allows the astrophysics of this region to be probed by the polarizationproperties of the silicon monoxide maser components located in the extended atmospheres viasynoptic imaging campaigns across complete pulsation periods of the central star. Here Very LongBaseline Array observations of maser emissions in the near-circumstellar regions of asymptoticgiant branch (evolved) stars will be carried out. The goal is to provide constraints on variousastrophysical models by: 1) measuring the magnitudes and orientation of magnetic fields in theextended atmospheres, 2) determining whether asymmetric mass loss begins at an early phase ofasymptotic giant branch evolution, and 3) exploring the possible connection between the centralstars and their close circumstellar environments. A series of specific research tasks (and associatedsub-tasks) are outlined which employ synoptic maser observations over entire pulsation cycles to(among other goals) map kinematics and shocks, to use polarization and population inversion toinfer magnetic fields and turbulence, and to discriminate between various models for polarizedmaser propagation and silicon oxide maser pumping. The latter studies are vital in order to provideunambiguous estimates of the surface magnetic fields in these stars. The results of this work areexpected to have an impact on studies of the physics of maser polarization, models of evolved starsand the process of planetary nebula formation.This work will help to train graduate students in the data reduction methods and analysis. Inaddition, the animated movies of maser emission toward late-type stars which are a by-product ofthis research, will be disseminated to the public through various outreach efforts. The final stepsnecessary to automate fully the existing calibration and imaging pipeline, which will be developedhere, will also be available to the community. This will sharply lower access barriers to the VeryLong Baseline Array.