scholarly journals Extremely Metal-Poor Asymptotic Giant Branch Stars

Universe ◽  
2022 ◽  
Vol 8 (1) ◽  
pp. 44
Author(s):  
Mario Cirillo ◽  
Luciano Piersanti ◽  
Oscar Straniero
Keyword(s):  
Physical Structure ◽  
Asymptotic Giant Branch ◽  
Chemical Pollution ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundances ◽  
First Stars ◽  
Convective Mixing ◽  
Nearby Galaxies ◽  
Complete Set ◽  
Giant Branch Stars

Little is known about the first stars, but hints on this stellar population can be derived from the peculiar chemical composition of the most metal-poor objects in the Milky Way and in resolved stellar populations of nearby galaxies. In this paper, we review the evolution and nucleosynthesis of metal-poor and extremely metal-poor (EMP) stars with low and intermediate masses. In particular, new models of 6 M⊙ with three different levels of metallicity, namely Z=10−4, 10−6 and 10−10, are presented. In addition, we illustrate the results obtained for a 2 M⊙, Z=10−5 model. All these models have been computed by means of the latest version of the FuNS code. We adopted a fully coupled scheme of solutions for the complete set of differential equations describing the evolution of the physical structure and the chemical abundances, as modified by nuclear processes and convective mixing. The scarcity of CNO in the material from which these stars formed significantly affects their evolution, their final fate and their contribution to the chemical pollution of the ISM in primordial galaxies. We show the potential of these models for the interpretation of the composition of EMP stars, with particular emphasis on CEMP stars.

scholarly journals The Structure of Dense Cloud Cores

1989 ◽  
Vol 120 ◽  
pp. 210-214
Author(s):  
Alwyn Wootten
Keyword(s):  
Physical Structure ◽  
Spectral Lines ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Single Plate ◽  
High Resolution Images ◽  
Circumstellar Shells ◽  
Cloud Cores ◽  
Giant Branch Stars

Open slit spectra of planetary nebulae, in which images of the object are recorded in the light of several spectral lines on a single plate, have long proven a useful diagnostic of nebular properties and morphology. Fortunately, the reasonably simple structure of most planetaries greatly aids interpretation of the images. The dust-enshrouded mass-losing asymptotic giant branch stars from which planetaries evolve have now also been imaged at millimeter wavelengths. These high-resolution images have demonstrated the role of photochemistry in molding the composition of circumstellar shells. This powerful techinique is less well-developed as a tool for analyzing the structure of localized density concentrations in molecular clouds, the cores in which stars form. Even pre-astral cores, in which stars have not yet formed, may have an extended and intricate geometry which renders mapping tedious and masks their true structure. Their basic pre-astral structure may be complexly contorted by the character and extent of star formation within them. How, then, does our perception of the structure of a core depend upon the line in whose light it is imaged? Which lines optimally determine physical structure? How should chemical differences, perceived by comparisons of images in different lines, be used to determine the physical characteristics of a core?

scholarly journals The chemical evolution of the dwarf spheroidal galaxy Sextans

2020 ◽  
Vol 642 ◽  
pp. A176 ◽  
Author(s):  
R. Theler ◽  
P. Jablonka ◽  
R. Lucchesi ◽  
C. Lardo ◽  
P. North ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Dwarf Galaxy ◽  
Small Mass ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundances ◽  
Low Metallicity ◽  
Red Giant ◽  
Giant Branch Stars

We present our analysis of the FLAMES dataset targeting the central 25′ region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giant branch stars down to V ∼ 20.5 mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H] = −3.2 to −1.5 dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [α/Fe] at ∼0.4 dex followed by a decrease above [Fe/H] ∼ −2 dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H] ∼ −2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.

scholarly journals The stellar spectral features of nearby galaxies in the near infrared: tracers of thermally pulsing asymptotic giant branch stars?

2015 ◽  
Vol 450 (3) ◽  
pp. 3069-3079 ◽  
Author(s):  
Rogério Riffel ◽  
Rachel E. Mason ◽  
Lucimara P. Martins ◽  
Alberto Rodríguez-Ardila ◽  
Luis C. Ho ◽  
...  
Keyword(s):  
Near Infrared ◽  
Asymptotic Giant Branch ◽  
Spectral Features ◽  
Asymptotic Giant Branch Stars ◽  
Nearby Galaxies ◽  
Giant Branch Stars

scholarly journals Nucleosynthesis in Red Giant Stars

2002 ◽  
Vol 187 ◽  
pp. 57-69
Author(s):  
Nami Mowlavi
Keyword(s):  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Standard Models ◽  
Red Giant ◽  
Giant Branch Stars

The production of elements from helium-3 to fluorine in low- and intermediate-mass stars is reviewed and compared to chemical abundances observed at the surface of both red giant branch and asymptotic giant branch stars. It is highlighted that, while the trends predicted by standard models are generally well confirmed, many chemical abundances observed at the surface of red giants require the operation of non-standard mixing in the stellar interior. In addition, chemical abundance predictions from presently available asymptotic giant branch models further suffer from the uncertainties affecting the third dredge-up phenomenon, the source of neutrons and the hot bottom burning process.

Observations of High Rotational CO Lines in Post–Asymptotic Giant Branch Stars and Planetary Nebulae

1997 ◽  
Vol 476 (1) ◽  
pp. 319-326 ◽  
Author(s):  
K. Justtanont ◽  
A. G. G. M. Tielens ◽  
C. J. Skinner ◽  
Michael R. Haas
Keyword(s):  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Giant Branch Stars

scholarly journals Carbon stars as standard candles – II. The median J magnitude as a distance indicator

2020 ◽  
Vol 501 (1) ◽  
pp. 933-947
Author(s):  
Javiera Parada ◽  
Jeremy Heyl ◽  
Harvey Richer ◽  
Paul Ripoche ◽  
Laurie Rousseau-Nepton
Keyword(s):  
Luminosity Function ◽  
Asymptotic Giant Branch ◽  
Distance Modulus ◽  
Asymptotic Giant Branch Stars ◽  
Luminosity Functions ◽  
Best Fitting ◽  
Distance Indicator ◽  
Ngc 6822 ◽  
The Given ◽  
Giant Branch Stars

ABSTRACT We introduce a new distance determination method using carbon-rich asymptotic giant branch stars (CS) as standard candles and the Large and Small Magellanic Clouds (LMC and SMC) as the fundamental calibrators. We select the samples of CS from the ((J − Ks)0, J0) colour–magnitude diagrams, as, in this combination of filters, CS are bright and easy to identify. We fit the CS J-band luminosity functions using a Lorentzian distribution modified to allow the distribution to be asymmetric. We use the parameters of the best-fitting distribution to determine if the CS luminosity function of a given galaxy resembles that of the LMC or SMC. Based on this resemblance, we use either the LMC or SMC as the calibrator and estimate the distance to the given galaxy using the median J magnitude ($\overline{J}$) of the CS samples. We apply this new method to the two Local Group galaxies NGC 6822 and IC 1613. We find that NGC 6822 has an ‘LMC-like’ CS luminosity function, while IC 1613 is more ‘SMC-like’. Using the values for the median absolute J magnitude for the LMC and SMC found in Paper I we find a distance modulus of μ0 = 23.54 ± 0.03 (stat) for NGC 6822 and μ0 = 24.34 ± 0.05 (stat) for IC 1613.

Finite Temperature Behavior of Carbon Atom Doped Silicon Clusters: Depressed Thermal Stabilities, Co-existing isomers, Reversible Dynamical Pathways and Fragmentation Channels

2021 ◽  
Author(s):  
Krati Joshi ◽  
Ashakiran Maibam ◽  
Sailaja Krishnamurty
Keyword(s):  
Silicon Carbide ◽  
Carbon Atom ◽  
Finite Temperature ◽  
Asymptotic Giant Branch ◽  
Temperature Behavior ◽  
Asymptotic Giant Branch Stars ◽  
Silicon Clusters ◽  
Thermal Stabilities ◽  
Doped Silicon ◽  
Giant Branch Stars

Silicon carbide clusters are significant due to their predominant occurrence in meteoric star dust, particularly in carbon rich asymptotic giant branch stars. Of late, they have also been recognized as...

scholarly journals A new synthetic model for asymptotic giant branch stars

2004 ◽  
Vol 350 (2) ◽  
pp. 407-426 ◽  
Author(s):  
Robert G. Izzard ◽  
Christopher A. Tout ◽  
Amanda I. Karakas ◽  
Onno R. Pols
Keyword(s):  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Synthetic Model ◽  
Giant Branch Stars
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