@inproceedings{913472ac32b84663a97a2a8dd6dc90a2,
title = "Proper Motions of Water Masers in Circumstellar Shells",
abstract = "We present proper motion measurements of circumstellar water masers obtained with the VLBA. The objects observed include S Persei, VX Sagittarii, U Herculis, VY Canis Majoris, NML Cygni, IK Tauri and RX Bootis. Results of the observations and modeling indicate that the water masers exist in a kinematically complex region of the circumstellar envelope, which is not well fit by the standard model of a uniformly expanding spherical wind. Attempts at fitting an ellipsoidal geometric distribution with a variety of kinematic models are presented. Estimates for the distances of the stars are also discussed. A change in position of the maser spots as a function of velocity has been measured. This effect may be used to place limits on accelerations in the masing gas. ",
keywords = "MASERS, EVOLVED STARS, CIRCUMSTELLAR SHELLS",
author = "K.B. Marvel and P.J. Diamond and A.J. Kemball",
year = "1998",
language = "English (US)",
isbn = "1-886733-74-0",
series = "Astronomical Society of the Pacific Conference Series",
pages = "1621--1628",
editor = "R.A. Donahue and J.A. Bookbinder",
booktitle = "The Tenth Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun",
}