AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 50. High Angular Resolution Science with the NRAO Very Long Baseline Array
Display, Tuesday, June 1, 1999, 10:00am-7:00pm, Southwest Exhibit Hall

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[50.11] Proper motion of water masers in the star forming region IRAS 21391+5802

N. Patel, L. Greenhill (SAO), J. Herrnstein (NRAO), Q. Zhang (SAO), J.M. Moran, P.T.P. Ho (SAO), P.F. Goldsmith (NAIC)

We present VLBA observations of water maser emission associated with the star forming region IRAS 21391+5802 embedded in a bright rimmed cometary globule in IC1396. The angular resolution in the maps is about 1 milliarcsecond, corresponding to a spatial resolution of 0.75 AU. Proper motions are derived for most of the maser features identified coherently over all three epochs which were separated by about one month. The mean magnitude of proper motions is about 10 milliarcseconds/yr (7.5 AU/yr). The error on derived proper motions is about 0.2 milliarcseconds/yr (0.15 AU/yr). The masers appear in three groups aligned linearly on the sky, roughly along the northeast--southwest direction, with a total separation of about 700 milliarcseconds (520 AU). Their proper motions and radial velocities show a systematic outward motion. The masers within the central group are well aligned linearly along the eastwest direction. Within this feature, there is a systematic velocity shift of about ~ 5 km s-1 over a projected distance of ~ 20 AU.

The overall pattern of proper motions is indicative of bipolar outflowing motion. The outer maser groups, separated by about 520 AU, are moving away from the central group of masers with a proper motion of about 5 and 8 AU/yr respectively. The masers seem to show acceleration in the outflow over a distance of 200 to 500 AU. Proper motions of the masers in the central group within a projected radius of ~ 10 AU, show systematic deviations from the outflowing motion. These masers appear to have a velocity component along northsouth direction. The distribution of these masers and their kinematics appear to be consistent with rotation.

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