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 Circumstellar molecular line emission from S-type AGB stars: mass-loss rates and SiO abundances

2009 ◽  
Vol 499 (2) ◽  
pp. 515-527 ◽  
Author(s):  
S. Ramstedt ◽  
F. L. Schöier ◽  
H. Olofsson
Keyword(s):  
Mass Loss ◽  
Line Emission ◽  
Agb Stars ◽  
Molecular Line ◽  
Loss Rates

scholarly journals De-Centered Central Stars of Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 541-542 ◽  
Author(s):  
Aubrie McLean ◽  
Martín A. Guerrero ◽  
Robert A. Gruendl ◽  
You-Hua Chu
Keyword(s):  
Binary System ◽  
Mass Loss ◽  
Planetary Nebulae ◽  
Central Star ◽  
Large Sample ◽  
Preliminary Results ◽  
Wide Range ◽  
Central Stars

The origin of the wide range of morphologies observed in planetary nebulae (PNe) is not well established. The influence of a binary companion of the central star can naturally explain this variety of morphologies, but very few PNe have known binary central stars. The evolution of the binary system with mass loss may result in the displacement of the central star from the nebular center. The large sample of PNe observed by HST is being used to search for de-centered central stars. Preliminary results indicate that the occurrence of de-centered central stars is widespread among all morphological types of PNe.

scholarly journals ALMA imaging of the nascent planetary nebula IRAS 15103–5754

2018 ◽  
Vol 480 (4) ◽  
pp. 4991-5009 ◽  
Author(s):  
José F Gómez ◽  
Gilles Niccolini ◽  
Olga Suárez ◽  
Luis F Miranda ◽  
J Ricardo Rizzo ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Velocity ◽  
Planetary Nebula ◽  
Symmetry Axis ◽  
Stellar System ◽  
Line Emission ◽  
Ionized Gas ◽  
Molecular Line ◽  
Common Envelope ◽  
Loss Event

ABSTRACT We present continuum and molecular-line (CO, C18O, HCO+) observations carried out with the Atacama Large Millimeter/submillimeter Array toward the ‘water fountain’ star IRAS 15103–5754, an object that could be the youngest planetary nebula (PN) known. We detect two continuum sources, separated by 0.39 ± 0.03 arcsec. The emission from the brighter source seems to arise mainly from ionized gas, thus confirming the PN nature of the object. The molecular-line emission is dominated by a circumstellar torus with a diameter of ≃0.6 arcsec (2000 au) and expanding at ≃23 km s−1. We see at least two gas outflows. The highest-velocity outflow (deprojected velocities up to 250 km s−1), traced by the CO lines, shows a biconical morphology, whose axis is misaligned ≃14° with respect to the symmetry axis of the torus, and with a different central velocity (by ≃8 km s−1). An additional high-density outflow (traced by HCO+) is oriented nearly perpendicular to the torus. We speculate that IRAS 15103–5754 was a triple stellar system that went through a common envelope phase, and one of the components was ejected in this process. A subsequent low-collimation wind from the remaining binary stripped out gas from the torus, creating the conical outflow. The high velocity of the outflow suggests that the momentum transfer from the wind is extremely efficient, or that we are witnessing a very energetic mass-loss event.

scholarly journals Circumstellar spirals/shells/arcs: the message from binary stars

2016 ◽  
Vol 12 (S323) ◽  
pp. 199-206
Author(s):  
Hyosun Kim
Keyword(s):  
Mass Loss ◽  
Binary Stars ◽  
Planetary Nebula ◽  
Fossil Record ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Molecular Line ◽  
The Past ◽  
Recurrent Patterns

AbstractA consensus has grown in the past few decades that binarity is key to understanding the morphological diversities of the circumstellar envelopes (CSEs) surrounding stars in the Asymptotic Giant Branch (AGB) to Planetary Nebula (PN) phase. The possible roles of binaries in their shaping have, however, yet to be confirmed. Meanwhile, recurrent patterns are often found in the CSEs of AGB stars and the outer halos of PNe, providing a fossil record of the mass loss during the AGB phase. In this regard, recent molecular line observations using interferometric facilities have revealed the spatio-kinematics of such patterns. Numerical simulations of binary interactions producing spiral-shells have been extensively developed, revealing new probes for extracting the stellar and orbital properties from these patterns. I review recent theoretical and observational investigations on the circumstellar spiral-shell patterns and discuss their implications in linking binary properties to the asymmetric ejection events in the post-AGB phase.

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.

On the nature and mass loss of Bulge OH/IR stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 353-354
Author(s):  
Joris A. D. L. Blommaert ◽  
Martin A. T. Groenewegen ◽  
Kay Justtanont ◽  
L. Decin
Keyword(s):  
Mass Loss ◽  
Total Mass ◽  
Photometric Data ◽  
Galactic Latitude ◽  
Agb Stars ◽  
High Galactic Latitude ◽  
Total Mass Loss ◽  
Successful Search ◽  
Ir Stars ◽  
Transfer Modelling

AbstractWe report on the successful search for CO (2-1) and (3-2) emission associated with OH/IR stars in the Galactic Bulge. We observed a sample of eight extremely red AGB stars with the APEX telescope and detected seven. The sources were selected at sufficient high Galactic latitude to avoid interference by interstellar CO, which hampered previous studies of inner galaxy stars. We also collected photometric data and Spitzer IRS spectroscopy to construct the SEDs, which were analysed through radiative transfer modelling. We derived variability periods of our stars from the VVV and WISE surveys. Through dynamical modelling we then retrieve the total mass loss rates (MLR) and the gas-to-dust ratios. The luminosities range between approximately 4,000 and 5,500 L⊙ and periods are below 700 days. The total MLR ranges between 10−5 and 10−4 M⊙ yr−1. The results are presented in Blommaert et al. 2018 and summarized below.

AGB outflows as tests of chemical kinetics and radiative transfer models

2019 ◽  
Vol 15 (S350) ◽  
pp. 253-256
Author(s):  
M. Van de Sande ◽  
T. Danilovich ◽  
L. Decin
Keyword(s):  
Radiative Transfer ◽  
Laboratory Experiments ◽  
Reaction Rates ◽  
Chemical Processes ◽  
Asymptotic Giant Branch ◽  
Laboratory Astrophysics ◽  
Agb Stars ◽  
New Science ◽  
Chemical Models ◽  
Molecular Abundances

AbstractThe outflows of asymptotic giant branch (AGB) stars are important astrochemical laboratories, rich in molecular material and host to various chemical processes, including dust formation. Since the different chemistries are relatively easily probed, AGB outflows are ideal testbeds within the wider astrochemical community. Recent observations are pushing the limits of both our current chemical models and radiative transfer routines. Current chemical models are restricted by the completeness of their chemical networks and the accuracy of the reaction rates. The molecular abundances retrieved by radiative transfer routines are strongly dependent on collisional rates, which are often not measured or calculated for molecules of interest. To further our understanding of the chemistry within the outflow, collaboration with the laboratory astrophysics community is essential. This collaboration is mutually beneficial, as it in turn provides new science questions for laboratory experiments and computations.

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 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.

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