VLA positions and distributions of H2O masers associated with 15 Mira and semiregular variables

Details VLA positions and distributions of H2O masers associated with 15 Mira and semiregular variables VLA positions and distributions of H2O masers associated with 15 Mira and semiregular variables

May 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apjs...92..189b&link_type=abstract

The Astrophysical Journal Supplement Series, vol. 92, no. 1, p. 189-218

Astronomy and Astrophysics

Astronomy

63

Ejecta, Interstellar Masers, Mass Flow, Mira Variables, Position (Location), Radiation Distribution, Radio Astronomy, Semiregular Variable Stars, Stellar Evolution, Stellar Mass Ejection, Stellar Models, Water Masers, Angular Resolution, Astronomical Spectroscopy, Circular Polarization, Data Reduction, High Resolution, Radio Spectra, Sensitivity, Spectral Resolution, Very Large Array (Vla)

Scientific paper

Results of VLA observations of 22 GHz H2O masers associated with 15 Mira and semiregular variables are reported. The combination of angular resolution (approximately equals 70 mas), spectral resolution (0.3 km/sec), rms sensitivity (+/- 35 mJy/beam), and hour-angle coverage is the best yet obtained for H2O masers from a significant sample of stars. Comparison of accurate optical positions of the stars with estimates from the masers yields total differences typically less than or equal to 0 sec .15-an improvement over previous comparisons by a factor of about 2. There are indications of some combination of nonuniformities in the density distribution, deviations from sphericity, and anisotropies in the velocity field, but it is difficult to disentangle the effects of these phenomena and achieve unique interpretation. A plausible model is clumps or filaments distributed at radii which vary with direction from the star. From the angular distributions and velocity ranges, there is good evidence that at least some parcels of gas are accelerated to the terminal outflow velocity at rho greater than or equal to 20 AU and that there is a component of outflow at rho approximately equals 10 to 15 AU; some gas probably is fully accelerated at radii less than 10 AU. To illustrate the problems of interpretation, the well-known case of VX Sgr is reexamined. The data do not support a simple model of increasing outflow velocity with increasing maser shell radius. It is proposed that the outflow is weakly bipolar.

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