Monocyanopolyynes from a carbon arc in ammonia: about the relative abundance of polyynes series formed in a carbon arc and those detected in the circumstellar shells of AGB stars

2006 ◽  
Vol 5 (1) ◽  
pp. 37-45 ◽  
Author(s):  
Franco Cataldo
Keyword(s):  
Asymptotic Giant Branch ◽  
Similar Species ◽  
Red Giants ◽  
Agb Stars ◽  
Mechanism Of Formation ◽  
Neutral Species ◽  
Graphite Electrodes ◽  
Circumstellar Shells ◽  
Carbon Arc ◽  
Circumstellar Environment

Monocyanopolyynes are formed by arcing graphite electrodes in ammonia. This work completes the parallelism existing between the polyynes formed by laser ablation experiments of graphite targets and those produced from the submerged electric arc. In both cases the same products are obtained. The products consist of hydrogen-terminated polyynes if water is present, monocyanopolyynes (mixed with hydrogen-terminated polyynes) if the carbon arc is sparked in acetonitrile or ammonia and dicyanopolyynes if the arc is struck in liquid nitrogen. The mechanism of formation of polyynes in the submerged carbon arc involves essentially neutral species; similar species and pathways may also occur in the circumstellar environment where polyynes have been detected by radioastronomy. It is shown that the relative abundances of the polyynes formed in the submerged carbon arc or in a carbon arc in vacuum decrease by a factor between three and five as the chain length increases by a C2 unit. Exactly the same trend has been observed by radioastronomy both for polyynes and cyanopolyynes in the circumstellar environment around red giants and asymptotic giant branch (AGB) stars. This fact may be a simple coincidence or may suggest that the mechanism of formation of the polyynes in the carbon arc is the same as that occurring in the surroundings of carbon-rich stars.

scholarly journals Nucleosynthesis of Light-Element Isotopes in Evolved Stars Experiencing Extended Mixing

2009 ◽  
Vol 26 (3) ◽  
pp. 161-167 ◽  
Author(s):  
S. Palmerini ◽  
M. Busso ◽  
E. Maiorca ◽  
R. Guandalini
Keyword(s):  
Mass Transport ◽  
Isotopic Composition ◽  
Light Element ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Evolved Stars ◽  
Magnetic Buoyancy ◽  
Slow Mixing

AbstractWe present computations of nucleosynthesis in red giants and Asymptotic Giant Branch (AGB) stars of Population I experiencing extended mixing. The assumed physical cause for mass transport is the buoyancy of magnetized structures, according to recent suggestions. The peculiar property of such a mechanism is to allow for both fast and slow mixing phenomena, as required for reproducing the spread in Li abundances displayed by red giants and as discussed in an accompanying paper. We explore here the effects of this kind of mass transport on CNO and intermediate-mass nuclei and compare the results with the available evidence from evolved red giants and from the isotopic composition of presolar grains of AGB origin. It is found that a good general accord exists between predictions and measurements; in this framework we also show which type of observational data best constrains the various parameters. We conclude that magnetic buoyancy, allowing for mixing at rather different speeds, can be an interesting scenario to explore for explaining together the abundances of CNO nuclei and of Li.

scholarly journals Asymptotic Giant Branch Stars in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 363-364
Author(s):  
Neill Reid ◽  
J. R. Mould
Keyword(s):  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Satellite Systems ◽  
Luminosity Functions ◽  
Theoretical Predictions

Since the pioneering objective prism surveys by Westerlund (1960) and Blanco et al. (1980), the Magellanic Clouds have proved a fruitful site for exploring the evolution of AGB stars. We have used photometric techniques to extend the prism C-star surveys to M- and S-type AGB stars, constructing luminosity functions and obtaining spectra of individual stars for comparison with theoretical predictions. We have concentrated on the Large Magellanic Cloud (LMC), but we have recently obtained observations of luminous red giants in a region of the Small Magellanic Cloud (SMC). In this paper we compare the results from these studies of the two satellite systems.

scholarly journals Stardust in meteorites: A link between stars and the Solar System

2008 ◽  
Vol 4 (S251) ◽  
pp. 341-342
Author(s):  
Ernst Zinner
Keyword(s):  
Solar System ◽  
Interplanetary Dust ◽  
Asymptotic Giant Branch ◽  
Dust Particles ◽  
Red Giants ◽  
Agb Stars ◽  
Interplanetary Dust Particles ◽  
Mixing Processes ◽  
Isotopic Compositions ◽  
Stellar Sources

AbstractUltimately, all of the solids in the Solar System, including ourselves, consist of elements that were made in stars by stellar nucelosynthesis. However, most of the material from many different stellar sources that went into the making of the Solar System was thoroughly mixed, obliterating any information about its origin. An exception are tiny grains of preserved stardust found in primitive meteorites, micrometeorites, and interplanetary dust particles. These μm- and sub-μm-sized presolar grains are recognized as stardust by their isotopic compositions, which are completely different from those of the Solar System. They condensed in outflows from late-type stars and in SN ejecta and were included in meteorites, from which they can be isolated and studied for their isotopic compositions in the laboratory. Thus these grains constitute a link between us and our stellar ancestors. They provide new information on stellar evolution, nucleosynthesis, mixing processes in asymptotic giant branch (AGB) stars and supernovae, and galactic chemical evolution. Red giants, AGB stars, Type II supernovae, and possibly novae have been identified as stellar sources of the grains. Stardust phases identified so far include silicates, oxides such as corundum, spinel, and hibonite, graphite, silicon carbide, silicon nitride, titanium carbide, and Fe-Ni metal.

scholarly journals Barium Stars: Theoretical Interpretation

2009 ◽  
Vol 26 (3) ◽  
pp. 176-183 ◽  
Author(s):  
Laura Husti ◽  
Roberto Gallino ◽  
Sara Bisterzo ◽  
Oscar Straniero ◽  
Sergio Cristallo
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Mass Transfer Process ◽  
Asymptotic Giant Branch ◽  
Theoretical Interpretation ◽  
Evolutionary Stage ◽  
Elemental Distribution ◽  
Red Giants ◽  
Agb Stars ◽  
Consistent Solution

AbstractBarium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth.

scholarly journals High Resolution Radio and IR Observations of AGB Stars

2012 ◽  
Vol 8 (S287) ◽  
pp. 245-249
Author(s):  
W. Cotton ◽  
G. Perrin ◽  
R. Millan-Gabet ◽  
O. Delaa ◽  
B. Mennesson
Keyword(s):  
High Resolution ◽  
Molecular Layer ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Near Ir ◽  
The Subject ◽  
Infrared Interferometry ◽  
Giant Branch Stars

AbstractAsymptotic Giant Branch Stars (AGB) are evolved, mass losing red giants with tenuous molecular envelopes which have been the subject of much recent study using infrared and radio interferometers. In oxygen rich stars, radio SiO masers form in the outer regions of the molecular envelopes and are powerful diagnostics of the extent of these envelopes. Spectroscopically resolved infrared interferometry helps constrain the extent of various species in the molecular layer. We made VLBA 7 mm SiO maser, Keck Interferometer near IR and VLTI/MIDI mid IR high resolution observations of the stars U Ari, W Cnc, RX Tau, RT Aql, S Ser and V Mon. This paper presents evidence that the SiO is depleted from the gas phase and speculate that it is frozen onto Al2O3 grains and that radiation pressure on these grains help drive the outflow.

scholarly journals A new method to identify subclasses among AGB stars using Gaia and 2MASS photometry

2018 ◽  
Vol 616 ◽  
pp. L13 ◽  
Author(s):  
T. Lebzelter ◽  
N. Mowlavi ◽  
P. Marigo ◽  
G. Pastorelli ◽  
M. Trabucchi ◽  
...  
Keyword(s):  
Stellar Population ◽  
Chemical Properties ◽  
Large Magellanic Cloud ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Agb Stars ◽  
Population Synthesis ◽  
Stellar Population Synthesis ◽  
Low Mass ◽  
Spectral Ranges

Aims. We explore the wealth of high-quality photometric data provided by data release 2 (DR2) of the Gaia mission for long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Our goal is to identify stars of various types and masses along the asymptotic giant branch. Methods. For this endeavour, we developed a new multi-band approach combining Wesenheit functions WRP,BP−RP and WKs,J−Ks in the Gaia BP, RP, and 2MASS J, Ks spectral ranges, respectively, and use a new diagram, (WRP,BP−RP − WKs,J−Ks) versus Ks, to distinguish between different kinds of stars in our sample of LPVs. We used stellar population synthesis models to validate our approach. Results. We demonstrate the ability of the new diagram to discriminate between O- and C-rich objects, and to identify low-mass, intermediate-mass, and massive O-rich red giants, as well as extreme C-rich stars. Stellar evolution and population synthesis models guide the interpretation of the results, highlighting the diagnostic power of the new tool to discriminate between stellar initial masses, chemical properties, and evolutionary stages.

scholarly journals Period-luminosity diagram of long period variables in the Magellanic Clouds

2019 ◽  
Vol 631 ◽  
pp. A24 ◽  
Author(s):  
T. Lebzelter ◽  
M. Trabucchi ◽  
N. Mowlavi ◽  
P. R. Wood ◽  
P. Marigo ◽  
...  
Keyword(s):  
Large Data ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Red Giants ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Data Set ◽  
Long Period ◽  
Long Period Variables

Context. The period-luminosity diagram (PLD) has proven to be a powerful tool for studying populations of pulsating red giants. Gaia Data Release 2 (DR2) provides a large data set including many long-period variables (LPVs) on which this tool can be applied. Aims. We investigate the location of LPVs from the Large and Small Magellanic Clouds in the PLD using various optical and infrared luminosity indicators from Gaia and 2MASS, respectively. We thereby distinguish between stars of different masses and surface chemistry. Methods. The data set taken from the Gaia DR2 catalogue of LPVs allows for a homogeneous study from low- to high-mass LPVs. These sources are divided into sub-populations of asymptotic giant branch (AGB) stars according to their mass and their O- or C-rich nature using the Gaia-2MASS diagram developed by our group. This diagram uses a Wesenheit index WBP, RP based on Wesenheit functions in the Gaia and 2MASS photometric bands. Four different luminosity indicators are used to study the period-luminosity (P–L) relations. Results. We provide the first observational evidence of a P–L relation offset for both fundamental and 1O pulsators between low- and intermediate-mass O-rich stars, in agreement with published pulsation predictions. Among the luminosity indicators explored, sequence C′ is the narrowest in the P–WBP, RP diagram, and is thus to be preferred over the other PLDs for the determination of distances using LPVs. The majority of massive AGB stars and red supergiants form a smooth extension of sequence C of low- and intermediate-mass AGB stars in the P–WBP, RP diagram, suggesting that they pulsate in the fundamental mode. All results are similar in the two Magellanic Clouds.

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 Detached Shell Carbon Stars: Tracing Thermal Pulses on the Asymptotic Giant Branch

2021 ◽  
Vol 922 (1) ◽  
pp. 24
Author(s):  
Joel H. Kastner ◽  
Emily Wilson
Keyword(s):  
Light Curves ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Infrared Photometry ◽  
Carbon Stars ◽  
The Past ◽  
Circumstellar Shells ◽  
The Relationship ◽  
Thermal Pulses ◽  
Luminosity Evolution

Abstract We consider whether the subset of carbon-rich asymptotic giant branch (AGB) stars that exhibit detached, expanding circumstellar shells may reveal the past histories of these stars as having undergone helium shell flashes (thermal pulses) on the AGB. We exploit newly available Gaia parallaxes and photometry, along with archival infrared photometry, to obtain refined estimates of the luminosities of all (12) known detached shell carbon stars. We examine the relationship between these luminosities and the estimated dynamical ages (ejection times) of the detached shells associated with the 12 stars, which range from ∼1000 to ∼30,000 yr. When arranged according to detached shell dynamical age, the (implied) luminosity evolution of the known detached shell carbon stars closely follows the predicted “light curves” of individual thermal pulses obtained from models of AGB stars. The comparison between data and models suggests that detached shell carbon stars are descended from ∼2.5 to 4.0 M ⊙ progenitors. We conclude that detached shell carbon stars may serve as effective tracers of the luminosity evolution of AGB thermal pulses.

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.

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