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Paper: AGB Circumstellar Environments Probed through 21-cm Atomic Hydrogen Emission
Volume: 378, Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes
Page: 299
Authors: Gerard, E.; Le Bertre, T.
Abstract: Most of the matter in circumstellar shells around red giants is hydrogen (~ 70 % in mass), in atomic or molecular form. However, up to now, atomic hydrogen has remained largely undetected due to the weakness of its signal and to the competing emission from interstellar hydrogen on the same line of sight. With the upgraded Nançay Radiotelescope (NRT), we have undertaken a new high-sensitivity search for the atomic hydrogen emission line at 21 cm in the direction of red giants, AGB stars, and post-AGBs, including Planetary Nebulae. The fan beam shape (4′ ×22′) of the NRT allows a good East–West discrimination of circumstellar envelopes against the galactic Hi background. We present our results on a few nearby sources which reveal circumstellar Hi emission that extends out to ~1 pc. These observations are complementary to the CO data which probe the inner part of the envelopes. They can be used to probe the mass-loss history of long-period variables over long time scales (~ 105 years) and also to investigate the interaction between stellar outflows and the ambient interstellar medium.
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