Evolution of the Circumstellar Atomic and Molecular Envelopes Around Evolved Stars
type: CreativeWork
description: The asymptotic giant branch (AGB) mass loss history of stars is recorded in the structure of their circumstellar envelope (CSE). For the more evolved protoplanetary nebula (PPN) and planetary nebula (PN) phases, the CSE also chronicles its interaction with fast winds and photodissociating/photoionizing radiation. Most AGB stars lose mass in spherically symmetric outflows, whereas PNe are largely axisymmetric. To investigate the physical properties of these winds and the processes that shape the CSE prior to the PN stage, the neutral atomic and molecular gas are probed. Here we present observations of the atomic and molecular components of the CSE for objects at different epochs of evolution. Far-infrared (FIR) spectra were taken for 24 evolved stars, including the line emission of [O I], [C II], [Si I], [Si II], [S I], [Fe I], [Fe II], and [Ne II]. Atomic emission was found only in those sources where Teff ≥ 10000 K. With higher T eff the number of detectable lines increase as well as the intensity of the emission, which imply that these atomic lines originate from photodissociation regions (PDRs). The line measurements agree reasonably well with intensities predicted by PDR models. Shock models, however, do not compare well with the observed line intensities. The kinematics of the atomic gas are comparable to the molecular expansion velocities, expected for cooling lines associated with circumstellar PDRs. PDR mass estimates ranging from ∼0.01--1.3 M⊙ were derived from the [C II] 158 mum line emission. Half of these objects were selected for a complementary, study of the molecular gas component. In the 12CO J = 1 → 0 imaging survey, high resolution maps of their full molecular envelopes are presented. A variety of different nebular morphologies and kinematic structures were encountered. For the PPNe and PN, the neutral molecular envelopes are compared with images taken at optical, near-IR, and mid-IR wavelengths. These trace the different components of the envelope…
abstract: The asymptotic giant branch (AGB) mass loss history of stars is recorded in the structure of their circumstellar envelope (CSE). For the more evolved protoplanetary nebula (PPN) and planetary nebula (PN) phases, the CSE also chronicles its interaction with fast winds and photodissociating/photoionizing radiation. Most AGB stars lose mass in spherically symmetric outflows, whereas PNe are largely axisymmetric. To investigate the physical properties of these winds and the processes that shape the CSE prior to the PN stage, the neutral atomic and molecular gas are probed. Here we present observations of the atomic and molecular components of the CSE for objects at different epochs of evolution. Far-infrared (FIR) spectra were taken for 24 evolved stars, including the line emission of [O I], [C II], [Si I], [Si II], [S I], [Fe I], [Fe II], and [Ne II]. Atomic emission was found only in those sources where Teff ≥ 10000 K. With higher T eff the number of detectable lines increase as well as the intensity of the emission, which imply that these atomic lines originate from photodissociation regions (PDRs). The line measurements agree reasonably well with intensities predicted by PDR models. Shock models, however, do not compare well with the observed line intensities. The kinematics of the atomic gas are comparable to the molecular expansion velocities, expected for cooling lines associated with circumstellar PDRs. PDR mass estimates ranging from ∼0.01--1.3 M⊙ were derived from the [C II] 158 mum line emission. Half of these objects were selected for a complementary, study of the molecular gas component. In the 12CO J = 1 → 0 imaging survey, high resolution maps of their full molecular envelopes are presented. A variety of different nebular morphologies and kinematic structures were encountered. For the PPNe and PN, the neutral molecular envelopes are compared with images taken at optical, near-IR, and mid-IR wavelengths. These trace the different components of the envelope…
author: Fong, David Ken
language: eng
keywords: Physics, Astronomy and Astrophysics
date published: 2015-09-25T22:35:36Z
date modified: 2026-07-22T22:26:24Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/85172