Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........9d&link_type=abstract
Thesis (PH.D.)--RENSSELAER POLYTECHNIC INSTITUTE, 1995.Source: Dissertation Abstracts International, Volume: 56-09, Section: B,
Other
Hydrodynamics, Dust Scattering
Scientific paper
Asymptotic Giant Branch stars are significant members of the Galaxy. They are surrounded by a circumstellar envelope of dust and gas. CO line observations show that the ensuing wind leads to significant mass loss, making these stars a primary source for reprocessing of the interstellar medium, and hence an important modeling target. Where most previous models have concentrated upon few processes (e.g., steady state hydrodynamics, or negligible dust scattering and cross shielding of dissociating transitions) in order to explain gross chemical or physical structures, I have identified and include concurrently as many of the relevant processes as possible. The model is simplified by decoupling the hydrodynamics of the inner region from the chemistry of the outer region, while the radiation field is important in both. I apply this model to the source IRC +10216. Inside of 1016 cm, I solve the time-dependent equations of hydrodynamics and grain growth for the dust and gas, including source terms. Although the gas reaches a steady outflow speed at r ~ 3R_*, a long-term transient exists in the density structure, even after 4.3 times 10^8 sec. An approximate continuum radiative transfer treatment suggests that the dust temperature structure is important, modifying the terminal flow speed by more than a factor of 2. Beyond 1016 cm, I determine the chemical evolution of the gas, using a superset of all previous available chemical networks. Unique to this model, I include grain surface chemistry and detailed UV radiative transfer through dust. Both dust processing and H_2 dissociation are crucial in determining the UV radiation field. This model is more efficient than other work at producing complex hydrocarbons and cyanopolyynes (adsorbed and gas phase). Of nine species for which good observational data exist, all are brought into closer agreement with observations by this model. Finally, this model is more successful at fitting the position and value of peak carbon abundance observed by Keene et al (1994), than other competing models. Simulated CO lines are constructed for comparison with recent observations. A gas temperature distribution steeper (Tk~ r^ {-1}) than the "standard" value is necessary to explain the observations, suggesting that CO line radiation is the dominant coolant. Finally, current data do not conclusively differentiate between source distances of 150 and 300 pc, but simulations of higher-lying transitions are included which, pending future observations, may make this possible.
No associations
LandOfFree
Modeling the Outer Regions of Evolved, Carbon - Circumstellar Envelopes: Application to IRC +10216 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Modeling the Outer Regions of Evolved, Carbon - Circumstellar Envelopes: Application to IRC +10216, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modeling the Outer Regions of Evolved, Carbon - Circumstellar Envelopes: Application to IRC +10216 will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-837311