scholarly journals Polyynes and Polycyclic Aromatic Molecules in C-rich Circumstellar Envelopes

1994 ◽  
Vol 146 ◽  
pp. 134-148 ◽  
Author(s):  
Alain Omont
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Aromatic Molecules ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Polycyclic Aromatic ◽  
Circumstellar Shells ◽  
Evolution Stage ◽  
Circumstellar Environment

The aim of this review is to discuss our knowledge on molecules in the circumstellar environment of evolved stars. In particular the presence and the behaviour of various kinds of molecules with several or many carbon atoms, in relation to C-rich dust, is considered.Such objects include mainly: (i) circumstellar shells of AGB carbon stars, either visible (such as Y CVn) or infrared (such as IRC+10216 (CW Leo)); (ii) planetary nebulae (PNe, e.g. NGC 7027); (iii) pre-planetary nebulae (PPNe, also called post-AGB stars, such as CRL 2688 or the Red Rectangle), probably in an intermediate evolution stage between the two former classes. I will not discuss more peculiar classes, such as R CrB stars and novae, for which very little is known about the presence of such molecular species.

scholarly journals Rings and arcs around evolved stars – II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009, and NGC 7027

2020 ◽  
Vol 495 (2) ◽  
pp. 2234-2246 ◽  
Author(s):  
M A Guerrero ◽  
G Ramos-Larios ◽  
J A Toalá ◽  
B Balick ◽  
L Sabin
Keyword(s):  
Proper Motion ◽  
Planetary Nebulae ◽  
Carbon Star ◽  
Agb Stars ◽  
Spiral Pattern ◽  
High Quality ◽  
Hydrodynamic Simulations ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Regular Patterns

ABSTRACT We present a detailed comparative study of the arcs and fragmented ring-like features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using high-quality multi-epoch HST images. This comparison allows us to investigate the connection and possible evolution between the regular patterns surrounding AGB stars and the irregular concentric patterns around PNe. The radial proper motion of these features, ≃15 km s−1, are found to be consistent with the AGB wind and their linear sizes and interlapse times (500–1900 yr) also agree with those found around AGB stars, suggesting a common origin. We find evidence using radiative-hydrodynamic simulations that regular patterns produced at the end of the AGB phase become highly distorted by their interactions with the expanding PN and the anisotropic illumination and ionization patterns caused by shadow instabilities. These processes will disrupt the regular (mostly spiral) patterns around AGB stars, plausibly becoming the arcs and fragmented rings observed in the haloes of PNe.

scholarly journals ISO's View of the Molecular Content of Evolved Stars

2000 ◽  
Vol 197 ◽  
pp. 375-390
Author(s):  
J. Cernicharo
Keyword(s):  
Systematic Study ◽  
Molecular Species ◽  
Planetary Nebulae ◽  
Far Infrared ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Mid Infrared ◽  
Evolved Stars ◽  
Vibrational Bands

The recent results of the ISO satellite in the field of molecular spectrocopy of AGB stars are reviewed. For the fist time, the two spectrometers onboard ISO have provided the opportunity to observe the pure rotational lines of several molecules in the far infrared and the ro-vibrational bands of the most abundant molecular species in the near and mid-infrared. These data allow to carry out a systematic study of the circumstellar envelopes of AGB stars and Planetary Nebulae. I analyze in this paper the role of resonant scatterring in the pumping of the ro-vibrational molecular levels in CSEs.

scholarly journals High-Resolution Radial Velocity and Hα Study of Proto-Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 354-354 ◽  
Author(s):  
B.J. Hrivnak ◽  
A.W. Woodsworth
Keyword(s):  
High Resolution ◽  
Physical Properties ◽  
Radial Velocity ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Binary Nature ◽  
Circumstellar Shells

We are engaged in a program to monitor radial velocity variability in proto-planetary nebulae (PPN). Observations are being made with the radial velocity spectrometer at the DAO, with a precision of ±0.5 km s−1. Radial velocity variability can arise from binary motion and/or pulsation in these post-AGB stars. The demonstration of a binary nature for some of these objects can have important implications for the understanding of their physical properties, and for the shaping of their circumstellar shells.

Millimetre Observations of Evolved Stars

1996 ◽  
Vol 13 (2) ◽  
pp. 185-186
Author(s):  
Jessica M. Chapman
Keyword(s):  
Mass Loss ◽  
Stellar Atmosphere ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
High Mass Loss ◽  
Transfer Momentum

Radio emission at centimetre and millimetre wavelengths provides a powerful tool for studying the circumstellar envelopes of evolved stars. These include stars on the asymptotic giant branch (AGB), post-AGB stars and a small number of massive M-type supergiant stars. The AGB stars and M-type supergiants are characterised by extremely high mass-loss rates. The mass loss in such an evolved star is driven by radiation pressure acting on grains which form in the outer stellar atmosphere. The grains are accelerated outwards and transfer momentum to the gas through grain–gas collisions. The outflowing dust and gas thus form an expanding circumstellar envelope through which matter flows from the star to the interstellar medium, at a typical velocity of 15 km s−1. For a recent review of circumstellar mass loss see Chapman, Habing & Killeen (1995).

scholarly journals Dust and molecules in extra-galactic planetary nebulae

2015 ◽  
Vol 11 (A29B) ◽  
Author(s):  
D. A. García-Hernández
Keyword(s):  
Solid State ◽  
Gas Phase ◽  
Organic Molecules ◽  
Local Group ◽  
Planetary Nebulae ◽  
Circumstellar Envelopes ◽  
The Galaxy ◽  
Models Comparison ◽  
Polycyclic Aromatic ◽  
Complex Organic

AbstractExtra-galactic planetary nebulae (PNe) permit the study of dust and molecules in metallicity environments other than the Galaxy. Their known distances lower the number of free parameters in the observations vs. models comparison, providing strong constraints on the gas-phase and solid-state astrochemistry models. Observations of PNe in the Galaxy and other Local Group galaxies such as the Magellanic Clouds (MC) provide evidence that metallicity affects the production of dust as well as the formation of complex organic molecules and inorganic solid-state compounds in their circumstellar envelopes. In particular, the lower metallicity MC environments seem to be less favorable to dust production and the frequency of carbonaceous dust features and complex fullerene molecules is generally higher with decreasing metallicity. Here, I present an observational review of the dust and molecular content in extra-galactic PNe as compared to their higher metallicity Galactic counterparts. A special attention is given to the level of dust processing and the formation of complex organic molecules (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene precursors) depending on metallicity.

scholarly journals Radio and IR interferometry of SiO maser stars

2012 ◽  
Vol 8 (S287) ◽  
pp. 209-216 ◽  
Author(s):  
Markus Wittkowski ◽  
David A. Boboltz ◽  
Malcolm D. Gray ◽  
Elizabeth M. L. Humphreys ◽  
Iva Karovicova ◽  
...  
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Agb Stars ◽  
Physical Reason ◽  
Maser Emission ◽  
Evolved Stars ◽  
Mira Variable ◽  
Infrared Interferometry ◽  
Molecular Layers ◽  
Circumstellar Environment

AbstractRadio and infrared interferometry of SiO maser stars provide complementary information on the atmosphere and circumstellar environment at comparable spatial resolution. Here, we present the latest results on the atmospheric structure and the dust condensation region of AGB stars based on our recent infrared spectro-interferometric observations, which represent the environment of SiO masers. We discuss, as an example, new results from simultaneous VLTI and VLBA observations of the Mira variable AGB star R Cnc, including VLTI near- and mid-infrared interferometry, as well as VLBA observations of the SiO maser emission toward this source. We present preliminary results from a monitoring campaign of high-frequency SiO maser emission toward evolved stars obtained with the APEX telescope, which also serves as a precursor of ALMA images of the SiO emitting region. We speculate that large-scale long-period chaotic motion in the extended molecular atmosphere may be the physical reason for observed deviations from point symmetry of atmospheric molecular layers, and for the observed erratic variability of high-frequency SiO maser emission.

scholarly journals Imaging Molecular Envelopes of Evolved Stars

1994 ◽  
Vol 140 ◽  
pp. 127-134
Author(s):  
John H. Bieging
Keyword(s):  
Planetary Nebulae ◽  
Chemical Processes ◽  
Emission Lines ◽  
Physical Processes ◽  
Molecular Line ◽  
Evolved Stars ◽  
Line Imaging ◽  
The Impact ◽  
Late Stages ◽  
Circumstellar Environment

AbstractResolved images of molecular emission lines from the envelopes of cool evolved stars reveal much about the physical processes by which such stars lose mass, about the chemical processes which occur in the outflowing gas, and about the evolution of the star to the planetary nebula stage. This paper reviews observational work on molecular line imaging at mm-wavelengths of carbon stars, Miras, proto-planetary nebulae, and planetary nebulae. The impact of these observations on our understanding of the late stages of stellar evolution as it affects the circumstellar environment is emphasized.

The Impact of UV Radiation on Circumstellar Chemistry

2018 ◽  
Vol 14 (S343) ◽  
pp. 191-195
Author(s):  
Maryam Saberi ◽  
Wouter Vlemmings ◽  
Tom Millar ◽  
Elvire De Beck
Keyword(s):  
Uv Radiation ◽  
Critical Role ◽  
Ionic Species ◽  
Asymptotic Giant Branch ◽  
Internal Source ◽  
Agb Stars ◽  
Parent Species ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
The Impact

AbstractUV radiation plays a critical role in the chemistry of circumstellar envelopes (CSEs) around evolved stars on the asymptotic giant branch (AGB). However, the effects of all potential sources of UV radiation have not been included in models. We present preliminary results of adding an internal source of UV to the CSE chemistry and predict large enhancements of atomic and ionic species arising from photo-destruction of parent species. Observations of atomic carbon towards the UV-bright AGB star o Cet are consistent with the modelling. In addition, we calculate the precise depth dependence of the CO photodissociation rate in an expanding CSE. We incorporate this within a chemical network active in the outflows of AGB stars, which includes 933 species and 15182 reactions. Our results show that the CO envelope size is about 30% smaller at half abundance than the most commonly used radius reported by Mamon et al. (1988).

scholarly journals Magnetic fields during the evolution towards planetary nebulae

2011 ◽  
Vol 7 (S283) ◽  
pp. 176-179 ◽  
Author(s):  
Wouter Vlemmings
Keyword(s):  
Magnetic Fields ◽  
Energy Budget ◽  
Magnetic Energy ◽  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Evolved Stars ◽  
Short Summary ◽  
New Instruments

AbstractMagnetic fields appear ubiquitous throughout the envelopes of evolved stars. However, their origin and role in the formation of planetary nebulae is still unclear. As observations of magnetic fields are complicated and time consuming, the observed samples of AGB and post-AGB stars and planetary nebulae are still small. Still, magnetic energy seems to dominate the energy budget out to a distance of several tens of AU from the central star and the field morphology often appears to be well ordered. A short summary is given of the current observations and the potential of new instruments such as ALMA is discussed.

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