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Paper: Probing Circumstellar Environments with Combined H I and CO Observations
Volume: 445, Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants
Page: 275
Authors: Libert, Y.; Le Bertre, T.; Gérard, E.; Winters, J. M.; Matthews, L. D.
Abstract: Circumstellar shells around red giants are built over long periods of time that may reach several million years. They may therefore be extended over large sizes (∼ 1 pc, possibly more) and different tracers are needed to describe their global properties. We designed a program to gauge the properties of matter in the external parts of circumstellar shells around AGB stars and to relate them to those of the inner envelopes, using the complementarity of the 21-cm H I line and the CO rotational lines. With millimeter observations at high spatial resolution, we find structures that could be the precursors of the complex morphologies observed for several planetary nebulae. Thanks to the 21-cm observations, we found evidence that the gas outflow is slowed down by the ambient interstellar medium. In some cases, the H I source is elongated in a direction compatible with the central-star proper motion, a phenomenon that is being recognized more and more often and that suggests an interaction with the local material. We illustrate these properties with several objects that have been well observed in CO and H I.
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