On the Mass and Metallicity Distributions of the Parent AGB Stars of O-Rich Presolar Stardust Grains

AbstractPresolar grains in meteorites formed in a sample of Asymptotic Giant Branch (AGB) stars that ended their lives within ≈1 Gyr of the origin of the Solar System 4.6 Gyr ago. The O-isotopic compositions of presolar O-rich stardust reflect the masses and metallicities of their parent stars. We present simple Monte Carlo simulations of the parent AGB stars of presolar grains. Comparison of model predictions with the grain data allow some broad conclusions to be drawn: (1) Presolar O-rich grains formed in AGB stars of mass ∼1.15–2.2 M⊙. The upper-mass cutoff reflects dredge-up of C in more massive AGB stars, leading to C-rich dust rather than O-rich, but the lack of grains from intermediate-mass AGB stars (>4 M⊙) is a major puzzle; (2) The grain O-isotopic data are reproduced well if the Galaxy in presolar times was assumed to have a moderate age-metallicity relationship, but with significant metallicity scatter for stars born at the same time; (3) The Sun appears to have a moderately low metallicity for its age and/or unusual 17O/16O and 18O/16O ratios for its metallicity; and (4) The Solar 17O/18O ratio, while unusual relative to present-day molecular clouds and protostars, was not atypical for the presolar disk and does not require self-pollution of the protosolar molecular cloud by supernova ejecta.

Download Full-text

EVOLUTION OF THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS. V. CONSTRAINING THE MASS LOSS AND LIFETIMES OF INTERMEDIATE-MASS, LOW-METALLICITY AGB STARS

The Astrophysical Journal ◽

10.3847/0004-637x/822/2/73 ◽

2016 ◽

Vol 822 (2) ◽

pp. 73 ◽

Cited By ~ 42

Author(s):

Philip Rosenfield ◽

Paola Marigo ◽

Léo Girardi ◽

Julianne J. Dalcanton ◽

Alessandro Bressan ◽

...

Keyword(s):

Mass Loss ◽

Asymptotic Giant Branch ◽

Asymptotic Giant Branch Stars ◽

Agb Stars ◽

Intermediate Mass ◽

Low Metallicity ◽

Giant Branch Stars

Download Full-text

Constraining ν-process production of fluorine through cosmic ray nucleosynthesis

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2893 ◽

2019 ◽

Vol 490 (3) ◽

pp. 4307-4316 ◽

Cited By ~ 4

Author(s):

Keith A Olive ◽

Elisabeth Vangioni

Keyword(s):

Stellar Evolution ◽

Massive Star ◽

Cosmic Ray ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Intermediate Mass ◽

Intermediate Mass Stars ◽

Star Production ◽

Low Metallicity ◽

Galactic Cosmic Ray

ABSTRACT Fluorine is massive enough that it is not considered to be a light (Z ≤ 5) element, yet compared to its near neighbours, C, N, O, and Ne, it is far underproduced in the course of stellar evolution, making its origin more complex. In fact, the abundance of fluorine is the lowest among all elements between Z = 5 and 21 and is roughly 3–4 orders of magnitude below that of C, N, O, and Ne. There are several plausible sources for F beyond standard stellar evolution. These include the production in the asymptotic giant branch phase (AGB) in intermediate-mass stars, production in Wolf–Rayet stars, and the production through neutrino spallation in supernovae. The latter, known as the ν-process, is an important source for 11B, and may contribute to the abundance of 7Li as well. We combine a simple model of Galactic chemical evolution with a standard Galactic cosmic ray nucleosynthesis model to treat self-consistently the evolution of the Li, Be, and B isotopes. We include massive star production of F, as well as contributions from AGB stars, and the ν-process. Given the uncertainties in neutrino energies in supernovae, we normalize the ν-process using the observed 11B/10B ratio as a constraint. As a consequence, we are able to determine the relative importance of each contribution to the F abundance. We find that although the ν-process dominates at early times (low metallicity), the present-day F abundance is found to originate primarily from AGB stars.

Download Full-text

What can pre-solar grains tell us about AGB stars?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307010940 ◽

2006 ◽

Vol 2 (14) ◽

pp. 345-348

Author(s):

Maria A. Lugaro ◽

Susanne Höfner

Keyword(s):

Neutron Capture ◽

Current Trend ◽

3D Models ◽

Point Of View ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Capture Process ◽

Model Predictions ◽

The Galaxy ◽

Isotopic Evolution

AbstractThe vast majority of pre-solar grains recovered to date show the signature of an origin in asymptotic giant branch (AGB) stars. In AGB stars, the abundances of elements lighter than silicon and heavier than iron are largely affected by proton- and neutron-capture processes, respectively, while the compositions of the elements in between also carry the signature of the initial composition of the star. Dust is produced and observed around AGB stars and the strong mass loss experienced by these stars is believed to be driven by radiation pressure on dust grains. We briefly review the main developments that have occurred in the past few years in the study of AGB stars in relation to dust and pre-solar grains. From the nucleosynthesis point of view these include: more stringent constraints on the main neutron source nucleus,13C, for theslowneutron capture process (thesprocess); the possibility of pre-solar grains coming from massive AGB stars; and the unique opportunity to infer the ‘isotopic’ evolution of the Galaxy by combining pre-solar grain data and AGB model predictions. Concerning the formation of grains in AGB stars, considerable progress has been achieved in modelling. In particular, self-consistent models for atmospheres and winds of C-stars have reached a level of sophistication which allows direct quantitative comparison with observations. In the case of stars with C/O < 1, however, recent work points to serious problems with the dust-driven wind scenario. A current trend in atmosphere and wind modelling is to investigate the possible effects of inhomogenieties (e.g., due to giant convection cells) with 2D/3D models.

Download Full-text

Evolved massive stars at low-metallicity

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935916 ◽

2019 ◽

Vol 629 ◽

pp. A91 ◽

Cited By ~ 6

Author(s):

Ming Yang ◽

Alceste Z. Bonanos ◽

Bi-Wei Jiang ◽

Jian Gao ◽

Panagiotis Gavras ◽

...

Keyword(s):

Massive Star ◽

Far Infrared ◽

Asymptotic Giant Branch ◽

Initial Mass ◽

Agb Stars ◽

Proper Motions ◽

Future Studies ◽

Low Metallicity ◽

Different Color ◽

Yellow Supergiant

We present a clean, magnitude-limited (IRAC1 or WISE1 ≤ 15.0 mag) multiwavelength source catalog for the Small Magellanic Cloud (SMC) with 45 466 targets in total, with the purpose of building an anchor for future studies, especially for the massive star populations at low-metallicity. The catalog contains data in 50 different bands including 21 optical and 29 infrared bands, retrieved from SEIP, VMC, IRSF, AKARI, HERITAGE, Gaia, SkyMapper, NSC, Massey (2002, ApJS, 141, 81), and GALEX, ranging from the ultraviolet to the far-infrared. Additionally, radial velocities and spectral classifications were collected from the literature, and infrared and optical variability statistics were retrieved from WISE, SAGE-Var, VMC, IRSF, Gaia, NSC, and OGLE. The catalog was essentially built upon a 1″ crossmatching and a 3″ deblending between the Spitzer Enhanced Imaging Products (SEIP) source list and Gaia Data Release 2 (DR2) photometric data. Further constraints on the proper motions and parallaxes from Gaia DR2 allowed us to remove the foreground contamination. We estimate that about 99.5% of the targets in our catalog are most likely genuine members of the SMC. Using the evolutionary tracks and synthetic photometry from MESA Isochrones & Stellar Tracks and the theoretical J − KS color cuts, we identified 1405 red supergiant (RSG), 217 yellow supergiant, and 1369 blue supergiant candidates in the SMC in five different color-magnitude diagrams (CMDs), where attention should also be paid to the incompleteness of our sample. We ranked the candidates based on the intersection of different CMDs. A comparison between the models and observational data shows that the lower limit of initial mass for the RSG population may be as low as 7 or even 6 M⊙ and that the RSG is well separated from the asymptotic giant branch (AGB) population even at faint magnitude, making RSGs a unique population connecting the evolved massive and intermediate stars, since stars with initial mass around 6 to 8 M⊙ are thought to go through a second dredge-up to become AGB stars. We encourage the interested reader to further exploit the potential of our catalog.

Download Full-text

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

Publications of the Astronomical Society of Australia ◽

10.1071/as08040 ◽

2009 ◽

Vol 26 (3) ◽

pp. 161-167 ◽

Cited By ~ 21

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.

Download Full-text

Neutron-capture elements in dwarf galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937075 ◽

2020 ◽

Vol 634 ◽

pp. A84 ◽

Cited By ~ 2

Author(s):

Á. Skúladóttir ◽

C. J. Hansen ◽

A. Choplin ◽

S. Salvadori ◽

M. Hampel ◽

...

Keyword(s):

Massive Star ◽

Milky Way ◽

Dwarf Galaxies ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Chemical Enrichment ◽

Theoretical Predictions ◽

Low Metallicity ◽

First Time ◽

Best Fit

The slow (s) and intermediate (i) neutron (n) capture processes occur both in asymptotic giant branch (AGB) stars, and in massive stars. To study the build-up of the s- and i-products at low metallicity, we investigate the abundances of Y, Ba, La, Nd, and Eu in 98 stars, at −2.4 < [Fe/H] < −0.9, in the Sculptor dwarf spheroidal galaxy. The chemical enrichment from AGB stars becomes apparent at [Fe/H] ≈ −2 in Sculptor, and causes [Y/Ba], [La/Ba], [Nd/Ba] and [Eu/Ba] to decrease with metallicity, reaching subsolar values at the highest [Fe/H] ≈ −1. To investigate individual nucleosynthetic sites, we compared three n-rich Sculptor stars with theoretical yields. One carbon-enhanced metal-poor (CEMP-no) star with high [Sr, Y, Zr] > +0.7 is best fit with a model of a rapidly-rotating massive star, the second (likely CH star) with the i-process, while the third has no satisfactory fit. For a more general understanding of the build-up of the heavy elements, we calculate for the first time the cumulative contribution of the s- and i-processes to the chemical enrichment in Sculptor, and compare with theoretical predictions. By correcting for the r-process, we derive [Y/Ba]s/i = −0.85 ± 0.16, [La/Ba]s/i = −0.49 ± 0.17, and [Nd/Ba]s/i = −0.48 ± 0.12, in the overall s- and/or i-process in Sculptor. These abundance ratios are within the range of those of CEMP stars in the Milky Way, which have either s- or i-process signatures. The low [Y/Ba]s/i and [La/Ba]s/i that we measure in Sculptor are inconsistent with them arising from the s-process only, but are more compatible with models of the i-process. Thus we conclude that both the s- and i-processes were important for the build-up of n-capture elements in the Sculptor dwarf spheroidal galaxy.

Download Full-text

Evolutionary timescales from the AGB to the CSPNe phase

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318007330 ◽

2018 ◽

Vol 14 (S343) ◽

pp. 36-46

Author(s):

Marcelo M. Miller Bertolami

Keyword(s):

White Dwarf ◽

New Physics ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Intermediate Mass ◽

Intermediate Mass Stars

AbstractThe transition from the asymptotic giant branch (AGB) to the final white dwarf (WD) stage is arguably the least understood phase in the evolution of single low- and intermediate-mass stars (0.8 ≲ MZAMS/M⊙ ≲ 8…10). Here we briefly review the progress in the last 50 years of the modeling of stars during the post-AGB phase. We show that although the main features, like the extreme mass dependency of post-AGB timescales were already present in the earliest post-AGB models, the quantitative values of the computed post-AGB timescales changed every time new physics was included in the modeling of post-AGB stars and their progenitors. Then we discuss the predictions and uncertainties of the latest available models regarding the evolutionary timescales of post-AGB stars.

Download Full-text

Water fountains: bipolar fast stellar jets traced by water vapor maser emission

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312019746 ◽

2012 ◽

Vol 8 (S290) ◽

pp. 227-228

Author(s):

Hiroshi Imai

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Asymptotic Giant Branch ◽

Young Stellar Objects ◽

Agb Stars ◽

Stellar Objects ◽

Stellar Jets ◽

The Masses ◽

Host Stars ◽

Maser Sources

AbstractHighly collimated, bipolar fast jets are found in asymptotic giant branch (AGB) and post-AGB stars as well as in active galactic nuclei and young stellar objects. It is still unclear how to launch such jets from dying stars that were originally spherically symmetric. Exploration of the stellar jet evolution is also expected to probe its role in shaping a planetary nebula. Interestingly, some of stellar H2O maser sources — water fountains — exhibit stellar jets with spatially and kinematically high collimation in the earliest phase (<1000 years) of the jet evolution. Such water fountains have been identified in 14 sources to date. We have recently conducted interferometric (VLBA, EVN, VERA, VLA) maser and the single-dish (ASTE) CO J = 3 → 2 line observations of the water fountains. They have revealed a typical dynamical age (< 100 yr) and the detailed kinematical structures of the water fountains, possibility of the coexistence of “equatorial flows”, and their locations and kinematics in the Milky Way. Based on these results, the masses and evolutionary statuses of the host stars are also estimated.

Download Full-text

Heavy elements in planetary nebulae: A theorist's gold mine

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312010824 ◽

2011 ◽

Vol 7 (S283) ◽

pp. 127-130

Author(s):

Amanda I. Karakas ◽

Maria Lugaro

Keyword(s):

Neutron Capture ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Heavy Elements ◽

Gold Mine ◽

Agb Stars ◽

Capture Process ◽

Wide Range ◽

Model Predictions

AbstractObservations of planetary nebulae have revealed a wealth of information about the composition of heavy elements synthesized by the slow neutron capture process (the s process). In some of these nebulae the abundances of neutron-capture elements are enriched by factors of 10 to 30 times the solar value, indicating that these elements were produced in the progenitor star while it was on the asymptotic giant branch (AGB). In this proceedings we summarize results of our recent full s-process network predictions covering a wide range of progenitor masses and metallicities. We compare our model predictions to observations and show how this can provide important insights into nucleosynthesis processes occurring deep within AGB stars.

Download Full-text