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Paper: Water Vapour Masers in the Mira Variable U Herculis
Volume: 445, Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants
Page: 375
Authors: Winnberg, A.; Brand, J.; Engels, D.
Abstract: The H2O maser line at 22 GHz from the Mira variable U Her has been monitored for more than 20 years. Additional interferometric observations were made at four epochs covering a period of 3 years. We found that the maser components have an average lifetime of 0.51 year and are distributed in a ring with distances from 12 to 25 AU from the star. The strongly varying shape of the single-dish maser spectra is the result of a superposition of many short-lived maser components with randomly varying intensities. The integrated flux is dominated by the random variations but varies also in response to the large-amplitude light variations with a period of 406 days.
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