scholarly journals The spectral evolution of post-AGB stars

1997 ◽  
Vol 180 ◽  
pp. 363-363
Author(s):  
R. D. Oudmaijer ◽  
P.A.M. van Hoof ◽  
L.B.F.M. Waters
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Evolutionary Rate ◽  
Central Star ◽  
Parameter Study ◽  
Agb Stars ◽  
Spectral Evolution ◽  
History Of ◽  
Photo Ionization

We have performed a parameter study of the spectral evolution of a typical post-AGB star with particular emphasis on the evolution of the IRAS colours. The models are based on the latest evolutionary tracks by Blöcker (1995, A&A 297, 727 and A&A 299, 755), which are used to define the evolutionary rate and the mass loss history of the central star. The resulting model for the post-AGB star is then used to calculate the spectral evolution with the photo-ionization code CLOUDY (Ferland 1993, Univ. of Kentucky, Int. Report), which includes dust in the radiative transfer.

scholarly journals Mid-Infrared Studies of the Cool Dust Distribution in Bipolar Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 365-366
Author(s):  
Kentaro Asano ◽  
Takashi Miyata ◽  
Takafumi Kamizuka ◽  
Toshiya Ueta
Keyword(s):  
Mass Loss ◽  
Planetary Nebulae ◽  
Central Star ◽  
Mid Infrared ◽  
Strong Emission ◽  
Formation History ◽  
Infrared Studies ◽  
Dust Component ◽  
History Of ◽  
Dust Distribution

AbstractTo understand mass loss history and mass loss and dust formation history of massive AGB stars, we carried out observations of three bipolar planetary nebulae (BPNe) in 30 micron bands from a ground-based telescope. All of our targets have a compact strong emission source in the mid-infrared (MIR) around the position of the central star of planetary nebula (CSPN). These detected emissions can be originated from cool dust. Our results show that the cool dust component is compactly distributed and much more massive than previous studies indicated. These findings suggest that they experienced a strong mass loss into the equatorial direction in past.

scholarly journals Probing chemical processes in AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 201-206 ◽  
Author(s):  
Fredrik L. Schöier ◽  
Hans Olofsson
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Line Emission ◽  
Chemical Processes ◽  
Agb Stars ◽  
Molecular Line ◽  
Large Sample ◽  
Preliminary Results ◽  
Transfer Modelling ◽  
Non Equilibrium

AbstractWe are conducting multi-transition observations of circumstellar line emission from common molecules such as HCN, SiO, CS, SiS and CN for a large sample of AGB stars with varying photospheric C/O-ratios and mass-loss charachteristics. Our recently published results for SiO and SiS clearly show that major constraints on the relative roles of non-equilibrium chemistry, dust condensation, and photodissociation can be obtained from the study of circumstellar molecular line emission. Presented here are also preliminary results based on detailed radiative transfer modelling of HCN line emission.

scholarly journals Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

2018 ◽  
Vol 609 ◽  
pp. A114 ◽  
Author(s):  
M. A. T. Groenewegen ◽  
G. C. Sloan
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Local Group ◽  
Mass Loss Rate ◽  
Large Fraction ◽  
Large Magellanic Cloud ◽  
Asymptotic Giant Branch ◽  
Spectral Energy ◽  
Agb Stars ◽  
Evolved Stars

Context. Mass loss is one of the fundamental properties of asymptotic giant branch (AGB) stars, and through the enrichment of the interstellar medium, AGB stars are key players in the life cycle of dust and gas in the universe. However, a quantitative understanding of the mass-loss process is still largely lacking. Aims. We aim to investigate mass loss and luminosity in a large sample of evolved stars in several Local Group galaxies with a variety of metalliticies and star-formation histories: the Small and Large Magellanic Cloud, and the Fornax, Carina, and Sculptor dwarf spheroidal galaxies (dSphs). Methods. Dust radiative transfer models are presented for 225 carbon stars and 171 oxygen-rich evolved stars in several Local Group galaxies for which spectra from the Infrared Spectrograph on Spitzer are available. The spectra are complemented with available optical and infrared photometry to construct spectral energy distributions. A minimization procedure was used to determine luminosity and mass-loss rate (MLR). Pulsation periods were derived for a large fraction of the sample based on a re-analysis of existing data. Results. New deep K-band photometry from the VMC survey and multi-epoch data from IRAC (at 4.5 μm) and AllWISE and NEOWISE have allowed us to derive pulsation periods longer than 1000 days for some of the most heavily obscured and reddened objects. We derive (dust) MLRs and luminosities for the entire sample. The estimated MLRs can differ significantly from estimates for the same objects in the literature due to differences in adopted optical constants (up to factors of several) and details in the radiative transfer modelling. Updated parameters for the super-AGB candidate MSX SMC 055 (IRAS 00483−7347) are presented. Its current mass is estimated to be 8.5 ± 1.6 M⊙, suggesting an initial mass well above 8 M⊙ in agreement with estimates based on its large Rubidium abundance. Using synthetic photometry, we present and discuss colour-colour and colour-magnitude diagrams which can be expected from the James Webb Space Telescope.

scholarly journals Binary post-AGB stars

1997 ◽  
Vol 180 ◽  
pp. 313-318 ◽  
Author(s):  
L.B.F.M. Waters ◽  
C. Waelkens ◽  
H. Van Winckel
Keyword(s):  
Mass Loss ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Agb Stars ◽  
Chemical Abundances ◽  
Intermediate Mass Stars ◽  
High Mass Loss ◽  
Complicating Factors ◽  
Circumstellar Environment

Low and intermediate mass stars leave the Asymptotic Giant Branch (AGB) when the mass in their H-rich envelope is less than about 0.01 M⊙, and the high mass loss drops several orders of magnitude. The central star rapidly evolves to the left part of the HR diagram along a track of constant luminosity (e.g. Schönberner 1983). In principle the evolution of the central star to higher Teff and the expansion and cooling of the AGB remnant are easy to calculate. In practice several complicating factors arise which make it much more difficult to predict the morphology and properties of post-AGB stars, such as binarity, post-AGB mass loss and aspherical AGB mass loss. Binarity of post-AGB stars affects the morphology of the circumstellar environment, and it affects evolutionary timescales and surface chemical abundances of the components in the system. This review discusses some properties of binary post-AGB stars.

scholarly journals The Influence of Dust Properties on the Mass Loss in Pulsating AGB Stars

2002 ◽  
Vol 185 ◽  
pp. 542-545
Author(s):  
Anja C. Andersen ◽  
Susanne Höfner ◽  
Rita Loidl
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Chemical Properties ◽  
Agb Stars ◽  
Complex Interplay ◽  
And Chemical Properties ◽  
Carbon Based

AbstractWe are currently studying carbon based dust types of relevance for carbon-rich AGB stars, to obtain a better understanding of the influence of the optical and chemical properties of the grains on the mass loss of the star. An investigation of the complex interplay between hydrodynamics, radiative transfer and chemistry has to be based on a better knowledge of the micro-physics of the relevant dust species.

scholarly journals AGB Stars and Their Circumstellar Envelopes. I. the VULCAN Code

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 80
Author(s):  
Sergio Cristallo ◽  
Luciano Piersanti ◽  
David Gobrecht ◽  
Lucio Crivellari ◽  
Ambra Nanni
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
High Complexity ◽  
Circumstellar Envelopes ◽  
Perfect Gas ◽  
Physical Processes ◽  
Transfer Effects

The interplay between AGB interiors and their outermost layers, where molecules and dust form, is a problem of high complexity. As a consequence, physical processes like mass loss, which depend on the chemistry of the circumstellar envelope, are often oversimplified. The best candidates to drive mass-loss in AGB stars are dust grains, which trap the outgoing radiation and drag the surrounding gas. Grains build up, however, is far from being completely understood. Our aim is to model both the physics and the chemistry of the cool expanding layers around AGB stars in order to characterize the on-going chemistry, from atoms to dust grains. This has been our rationale to develop ab initio VULCAN, a FORTRAN hydro code able to follow the propagation of shocks in the circumstellar envelopes of AGB stars. The version presented in this paper adopts a perfect gas law and a very simplified treatment of the radiative transfer effects and dust nucleation. In this paper, we present preliminary results obtained with our code.

scholarly journals Formation of crystalline silicate around oxygen–rich AGB stars

1999 ◽  
Vol 191 ◽  
pp. 239-244 ◽  
Author(s):  
Takashi Kozasa ◽  
Hisato Sogawa
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Emission Feature ◽  
High Mass ◽  
Agb Stars ◽  
Dust Grains ◽  
High Mass Loss ◽  
Calculation Results ◽  
History Of

Crystallization of silicate has been investigated within the framework of dust formation in steady state gas outflows around oxygen–rich AGB stars, where silicates are locked not only into homogeneous silicate grains but also into the mantles of heterogeneous grains. Based on the thermal history of dust grains after their formation, the crystallization calculation results in no crystalline silicate for the mass loss rate Ṁ ≤ 2 × 10−5M⊙ yr−1. Only silicate in the mantles of heterogeneous grains can be crystallized for Ṁ ≥ 3 × 10−5M⊙ yr−1, while homogeneous silicate grains remain amorphous. The mass fraction of crystalline silicate increases with increasing Ṁ. The radiation transfer calculations confirm the appearance of an emission feature around 33.5 μm, taking olivine as a representative of crystalline silicates. On the other hand, the 10μm feature appears in absorption, being dominated by homogeneous silicate grains. These trends are consistent with the observations. Thus the crystalline silicate is a diagnostics of high mass loss rate at the late stage of AGB stellar evolution, reflecting the formation process of dust grains.

scholarly journals Further Models of Planetary Nebula Spectral Evolution

1993 ◽  
Vol 155 ◽  
pp. 477-477
Author(s):  
K. Volk
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Radio Flux ◽  
Spectral Evolution ◽  
Star Evolution ◽  
Solar Composition ◽  
5 Ghz ◽  
Galactic Distribution

Four new calculations of planetary nebulae spectral evolution are presented, as in Volk (1992). These models use the 0.64 M⊙ central star evolution track of Schönberner (1983) but with the rate of evolution accelerated by a factor of 2, as the original models evolve to the planetary nebula phase too slowly to match the observations. Models were calculated for mass-loss rates of 2.1 × 10−5 and 5.2 × 10−5 MM⊙ yr−1 using solar composition and silicate dust, and using the average observed planetary nebula composition and graphite dust. An interacting winds shell was assumed to form. The model results were combined with an assumed Galactic distribution of 25000 planetary nebula to simulate a variety of observables including V magnitudes, Hβ fluxes, the IRAS colours, the 5 GHz radio flux densities, and the nebular radii.

scholarly journals Circumstellar H2O in M-type AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 163-164
Author(s):  
Matthias Maercker ◽  
Fredrik L. Schöier ◽  
Hans Olofsson
Keyword(s):  
Radiative Transfer ◽  
Radiation Field ◽  
Central Star ◽  
Thermal Excitation ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
Transfer Modelling

AbstractSurprisingly high amounts of H2O have recently been reported in the circumstellar envelope around the M-type AGB star W Hya. However, substantial uncertainties remain, as the required radiative transfer modelling is difficult due to high optical depths, sub-thermal excitation and the sensitivity to the combined radiation field from the central star and dust grains.

scholarly journals From the Tip of the AGB Towards a Planetary: A Hydrodynamical Simulation

2000 ◽  
Vol 177 ◽  
pp. 469-477
Author(s):  
D. Schönberner ◽  
M. Steffen ◽  
J. Stahlberg ◽  
K. Kifonidis ◽  
T. Blöcker
Keyword(s):  
Mass Loss ◽  
Dynamical Evolution ◽  
Central Star ◽  
Rapid Decline ◽  
Agb Stars ◽  
Natural Consequence ◽  
Hydrodynamical Simulation ◽  
Exploratory Investigation ◽  
Fast Wind ◽  
Thermal Pulses

We present a first exploratory investigation of the dynamical evolution of a dusty stellar wind envelope along the upper AGB and its transformation into a planetary nebula. We find the existence of AGB stars with detached shells to be a natural consequence of the mass-loss variations during a thermal pulse. It is also demonstrated that due to the large dynamical effects caused by the ionizing radiation field and the fast wind of the central star, it is impossible to deduce the AGB mass loss history from the planetary's density and velocity distribution. The structure of the halo, however, is still determined by the AGB mass loss history. The rapid decline of mass loss expected in the aftermath of thermal pulses leads to extended shells of low densities and explains halos with sharp boundaries.

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