Results 181 to 190 of about 14,221 (195)
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Dirty ice grains in the protoplanetary nebula
Planetary and Space Science, 1997Abstract The model of Mekler and Podolak (1994) for the growth of small ice grains in the nebula is extended to allow for the presence of additional absorbers. The properties of these “dirty” grains are explored. The presence of an additional absorber allows for several interesting effects.
Y. Mekler, Morris Podolak
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ISO Results for Protoplanetary Nebulae
2001We discuss the results of analysis of Infrared Space Observatory spectra of PPN candidates. In particular for the carbon-rich PPNs in our sample we have analysis of the 21 and 30 μm features as well as the UIR features and plateaus. The 30 μm feature appears to have two sub-components, at about 27 and about 34 μm, which vary from source to source ...
Ryszard Szczerba +3 more
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The distribution of gases in the protoplanetary nebula
Icarus, 1964Abstract It is demonstrated that the distribution of elements in the solar system may be connected with solar magnetic fields. Relative diffusion of neutral particles and ions in a magnetic field (“ambipolar diffusion”) separates elements of different ionization potential.
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Particle-Gas Dynamics in the Midplane of a Protoplanetary Nebula
Icarus, 1993Abstract In this paper, we study the stage of planetary formation during which the particulate material is still dispersed as centimeter-to-meter sized primordial aggregates. During this stage, particles are able to settle toward the midplane into a layer of mass density comparable to or much greater than that of the gas.
Jeffrey N. Cuzzi +2 more
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OH–IR sources as precursors to protoplanetary nebulae
Nature, 1990IT has long been suspected1 that OH–IR sources, highly evolved red giant stars that have built up massive, cool gaseous envelopes through heavy mass loss, are precursors to planetary nebulae. The two kinds of object share a similar galactic distribution, and their circumstellar envelopes have comparable masses and expansion velocities2,3.
R. J. Cohen +3 more
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Photometric variability of five candidates for protoplanetary nebulae
Astronomy Letters, 2011We analyze long-term UBV observations and ASAS-3 photometry for five candidates for protoplanetary nebulae—F and G supergiants with infrared excesses at highG alactic latitudes—V340 Ser, IRAS 05113+1347, V552 Pup, V448 Lac, and RV Col. These stars exhibit quasi-periodic multifrequency light variations caused by pulsations with characteristic time ...
V. P. Arkhipova +2 more
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Rossby Wave Propagation and Generation in the Protoplanetary Nebula
Icarus, 1999Abstract The protoplanetary nebular analog to the planetary Rossby wave is developed. Linear dispersion relations are derived. It is found that the nebular Rossby wave propagates freely in the nebular azimuthal direction and slowly grows in the radial direction. Possible ramifications for the nebula are raised for the reverse transition of turbulence
Sanford S. Davis +3 more
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Protoplanetary nebulae – the transition objects
2000The evolutionary stage between the end of the AGB and PN phases has long been a missing link in our understanding of single-star evolution. As we discussed in Chapter 10, the AGB is terminated by the depletion of the H envelope by mass loss, and this occurs before the onset of carbon detonation. When mass loss reduces the mass of the H envelope (M e )
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Blow-off of planetary protoatmospheres and of the protoplanetary nebula
Physics of the Earth and Planetary Interiors, 1982Abstract The mass loss from planetary protoatmospheres is in the order of 10 −2 –10 −4 parts of the planetary mass for the terrestrial planets and about 10 −7 –10 −8 parts for the giant planets. The minimum time intervals needed for the disappearance of the protoplanetary nebula are in the order of 10 6 y in the case of heating by a T-Tauri-like ...
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Molecular lines from protoplanetary nebulae: observations with ALMA
Astrophysics and Space Science, 2007Planetary nebulae (PNe) are formed in a very fast process. In just about 1000 years, the nebula evolves from a spherical and slowly expanding AGB envelope to a PN, with usually axial symmetry and high axial velocities. Molecular lines are known to probe most of the nebular material in young PNe and protoplanetary nebulae (PPNe), and are therefore very ...
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