Computer Science
Scientific paper
Jul 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001esasp.460..253b&link_type=abstract
The Promise of the Herschel Space Observatory. Eds. G.L. Pilbratt, J. Cernicharo, A.M. Heras, T. Prusti, & R. Harris. ESA-SP 460
Computer Science
Stars: Agb And Post-Agb, Stars: Circumstellar Matter, Radio, Lines:Stars, Planetary Nebulae
Scientific paper
Protoplanetary nebulae show fast bipolar flows that are known to carry high amounts of mass (a fraction of a solar mass), linear momentum and kinetic energy. In some nebulae, this momentum is so high that it cannot be provided by the stellar radiation pressure, given the expected short acceleration times and general conditions for the transfer of momentum to the gas. It is known that this component is, because of its low temperature, well probed by observations of mm-wave CO lines. We have studied all the protoplanetary nebulae that have been detected in CO up to date, a sample containing 37 objects. New accurate CO observations were performed for 16 of these objects. About 80% of the 27 objects for which the CO data allow a reasonable interpretation show these energetic flows. Radiation pressure could explain the whole dynamics of the nebulae in only 6 objects. Remarkably, 4 of these 6 objects are known to have low initial mass; excluding them, we find that less than 10% of the (well studied) protoplanetary nebulae do not show such very energetic bipolar flows. It is thought that these bipolar flows are accelerated by shock interaction between the old AGB wind (dense and slow) and post-AGB bipolar ejections (fast but relatively diffuse). Such an interaction would be the main dynamical phenomenon in the protoplanetary evolution, i.e. in the planetary nebula shaping. However, the shock fronts themselves have not been studied yet. CO probes the already cooled material, and the shocked regions observed in the optical and NIR contain very small amounts of mass and kinetic energy; moreover, because of their spatial distribution, they often seem to correspond to inner shocks and not to the relevant forward shock. A very fast cooling or a very high obscuration may avoid its detection at these wavelengths. ISO observations of molecular and atomic lines could have detected this component, but the lack of velocity information avoids any clear identification and reliable study. The observation with high spectral resolution of intermediate-excitation lines at intermediate wavelengths (FIR) is necessary for such a task.
Alcolea Javier
Bujarrabal Valentin
Castro-Carrizo Arancha
Sanchez Contreras Carmen
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