Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21424903c&link_type=abstract
American Astronomical Society, AAS Meeting #214, #249.03; Bulletin of the American Astronomical Society, Vol. 41, p.750
Astronomy and Astrophysics
Astronomy
Scientific paper
Planetary Nebulae (PN) evolve from intermediate mass stars, following a period of intensive mass loss during the AGB phase of stellar evolution. HST imaging surveys reveal that the vast majority of PNs deviate dramatically from spherical symmetry, and show a dazzling array of morphologies. The origin of the overall morphology of PNs and their detailed structure is a major problem for our understanding of the late stages of stellar evolution. Hydrodynamic sculpting of the progenitor AGB envelope by high-velocity jet-like outflows with changing directionality, early during the PPN phase, has been proposed as a primary mechanism for shaping PNs. We present results from current and ongoing efforts by several groups to use the NRAO Very Long Baseline Array to carry out astrometry (to 50 microarcsec precision) of water, OH, and/or SiO masers in an important class of very young PPNs, the water-fountain nebulae. Such proper motion (and radial velocity) measurements made over several epochs have been used to determine the geometric parallax of sources with unparalleled accuracy up to 8 kpc, and determine the 3-D motions of the high-velocity jets. Such studies provide unique and invaluable information to constrain theoretical models of how these high velocity jets sculpt the circumstellar medium in the evolution of these objects to PNs. Upgrades to the sensitivity of the VLBA will enhance the continuum sensitivity to extragalactic sources as astrometric references, and allow geometric parallaxes to be measured to 10-15 kpc for many objects. We will thus be able to measure physical parameters of these objects such as the stellar luminosity, ejecta masses and mass-loss rates, and expansion ages, which are fundamental to a full understanding of their evolution.
The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Claussen Mark J.
Day Fonda
Pihlstrom Ylva
Sahai Raghvendra
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