Proper motions of water vapour masers and bipolar outflow from NML Cygni

Details Proper motions of water vapour masers and bipolar outflow from NML Cygni Proper motions of water vapour masers and bipolar outflow from NML Cygni

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996mnras.282..665r&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 282, Issue 2, pp. 665-676.

Astronomy and Astrophysics

Astronomy

46

Masers, Circumstellar Matter, Stars: Kinematics, Stars: Late-Type, Stars: Mass-Loss, Radio Lines: Stars.

Scientific paper

MERLIN observations of the 22-GHz H_2O masers in the circumstellar envelope of the supergiant NML Cyg show an irregular ring of emission 200 mas across, plus a pair of outlying features to the north-west (NW) and south-east (SE) nearly 600 mas apart. Comparison with maps at previous epochs reveals proper motions of these outlying features, of 1.9+/-0.4 mas yr^-1. This corresponds to a transverse velocity of 19+/-4 km s^-1 at a distance of 2 kpc, which is consistent with the radial velocity range of the 22-GHz emission. The remaining masers which form the irregular ring are modelled as an expanding and accelerating thick shell. The NW-SE symmetry axis of the H_2O masers is aligned with a NW-SE asymmetry which occurs in the OH 1612-MHz masers on a larger scale of 3 arcsec. It appears that this is an internally driven effect, most likely a bipolar outflow which is more highly collimated near the star (H_2O masers) and becomes less collimated at greater distances (OH masers). The results are compared with bipolar outflows seen in other evolved objects.

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