scholarly journals Light Elements in the Universe

2021 ◽  
Vol 8 ◽  
Author(s):  
Sofia Randich ◽  
Laura Magrini
Keyword(s):  
Globular Clusters ◽  
Light Element ◽  
Big Bang ◽  
Stellar Structure ◽  
Age Dating ◽  
Sequence Evolution ◽  
Light Elements ◽  
Chemical Enrichment ◽  
Star Formation Histories ◽  
The Universe

Due to their production sites, as well as to how they are processed and destroyed in stars, the light elements are excellent tools to investigate a number of crucial issues in modern astrophysics: from stellar structure and non-standard processes at work in stellar interiors to age dating of stars; from pre-main sequence evolution to the star formation histories of young clusters and associations and to multiple populations in globular clusters; from Big Bang nucleosynthesis to the formation and chemical enrichment history of the Milky Way Galaxy and its populations, just to cite some relevant examples. In this paper, we focus on lithium, beryllium, and boron (LiBeB) and on carbon, nitrogen, and oxygen (CNO). LiBeB are rare elements, with negligible abundances with respect to hydrogen; on the contrary, CNO are among the most abundant elements in the Universe, after H and He. Pioneering observations of light-element surface abundances in stars started almost 70 years ago and huge progress has been achieved since then. Indeed, for different reasons, precise measurements of LiBeB and CNO are difficult, even in our Sun; however, the advent of state-of-the-art ground- and space-based instrumentation has allowed the determination of high-quality abundances in stars of different type, belonging to different Galactic populations, from metal-poor halo stars to young stars in the solar vicinity and from massive stars to cool dwarfs and giants. Noticeably, the recent large spectroscopic surveys performed with multifiber spectrographs have yielded detailed and homogeneous information on the abundances of Li and CNO for statistically significant samples of stars; this has allowed us to obtain new results and insights and, at the same time, raise new questions and challenges. A complete understanding of the light-element patterns and evolution in the Universe has not been still achieved. Perspectives for further progress will open up soon thanks to the new generation instrumentation that is under development and will come online in the coming years.

scholarly journals The Light Elements: What is Known, What is Controversial

2000 ◽  
Vol 198 ◽  
pp. 3-10 ◽  
Author(s):  
F. Spite
Keyword(s):  
Big Bang ◽  
Stellar Atmospheres ◽  
Stellar Structure ◽  
H Ii Regions ◽  
Light Elements ◽  
Stellar Abundances ◽  
Stellar Interiors ◽  
The Big Bang ◽  
The Universe

The light elements are essential, because their primordial abundances are linked to the general parameters of the universe (at least in the Big Bang theory). Some of the light elements are fragile, and the interpretation of their abundances in stars requires a good knowledge of the stellar structure. The stellar abundances have to be known with a considerable accuracy, challenging the current level of representation of the stellar atmospheres. It is also difficult to reach accurate abundances in the gas : interstellar, H II regions, PN, intergalactic¨.On the other hand, the fragile light elements are important probes of the stellar interiors, and their observation helps to the determination of reliable models, which in turn will improve the accuracy of stellar abundances. A part of this symposium is devoted to this probing aspect.The talks (and many high quality posters) which build this symposium, cover all these aspects. I will try here to point out the controversial points and the reasonably well known facts. We expect from discussions, both formal and informal, a number of (eagerly awaited for) clarifications.

scholarly journals Chemical abundances in tidally disrupted globular clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 157-160
Author(s):  
D. Yong ◽  
J. Meléndez ◽  
K. Cunha ◽  
A. I. Karakas ◽  
J. E. Norris ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Preliminary Analysis ◽  
Globular Clusters ◽  
Building Blocks ◽  
Light Elements ◽  
Chemical Abundances ◽  
Chemical Enrichment ◽  
Abundance Variation

AbstractWe present abundance measurements in the tidally disrupted globular cluster NGC 6712. In this cluster, there are large star-to-star variations of the light elements C, N, O, F and Na. While such abundance variations are seen in every well-studied globular cluster, they are not found in field stars and indicate that clusters like NGC 6712 cannot provide many field stars and/or field stars do not form in environments with chemical-enrichment histories like those of NGC 6712. Preliminary analysis of NGC 5466, another tidally disrupted cluster, suggests little (if any) abundance variation for O and Na and the abundance ratios [X/Fe] are comparable to field stars at the same metallicity. Therefore, globular clusters like NGC 5466 may have been Galactic building blocks.

scholarly journals Dark matter annihilation in the universe

2014 ◽  
Vol 30 ◽  
pp. 1460256 ◽  
Author(s):  
Pierre Salati
Keyword(s):  
Dark Matter ◽  
Galactic Halo ◽  
Light Element ◽  
Big Bang ◽  
Microwave Background ◽  
Dark Matter Annihilation ◽  
Element Abundances ◽  
Primordial Plasma ◽  
Relic Abundance ◽  
The Universe

The astronomical dark matter is an essential component of the Universe and yet its nature is still unresolved. It could be made of neutral and massive elementary particles which are their own antimatter partners. These dark matter species undergo mutual annihilations whose effects are briefly reviewed in this article. Dark matter annihilation plays a key role at early times as it sets the relic abundance of the particles once they have decoupled from the primordial plasma. A weak annihilation cross section naturally leads to a cosmological abundance in agreement with observations. Dark matter species subsequently annihilate — or decay — during Big Bang nucleosynthesis and could play havoc with the light element abundances unless they offer a possible solution to the 7 Li problem. They could also reionize the intergalactic medium after recombination and leave visible imprints in the cosmic microwave background. But one of the most exciting aspects of the question lies in the possibility to indirectly detect the dark matter species through the rare antimatter particles — antiprotons, positrons and antideuterons — which they produce as they currently annihilate inside the galactic halo. Finally, the effects of dark matter annihilation on stars is discussed.

Nucleosynthesis

1986 ◽  
Vol 320 (1556) ◽  
pp. 557-564 ◽  
Keyword(s):  
Light Element ◽  
Hubble Constant ◽  
Big Bang ◽  
Element Abundances ◽  
Stellar Nucleosynthesis ◽  
Baryonic Density ◽  
Redshift Surveys ◽  
A Value ◽  
First Case ◽  
The Universe

Both Big-Bang and stellar nucleosynthesis have outcomes related to the density of baryonic matter, but whereas in the first case there is a standard model that makes very precise predictions of light element abundances as a function of the mean density of baryons in the Universe, in the second case various uncertainties permit only very limited conclusions to be drawn. As far as Big-Bang synthesis and the light elements are concerned, existing results on D, 3 He and 7 Li indicate a value of Ω N h 2 0 greater than 0.01 and less than 0.025, where Ω N is the ratio of baryonic density to the closure density and h 0 is the Hubble constant in units of 100 km s -1 Mpc -1 ; probably 0.5 < h 0 < 1. New results on the primordial helium abundance give a still tighter upper limit to Ω N ,Ω N h 2 0 < 0.013, which when compared with redshift surveys giving Ω > 0.05 implies that the observed matter can all be baryonic only if the various uncertainties are stretched to their limits.

scholarly journals Impact of neutrino properties and dark matter on the primordial Lithium production

2019 ◽  
Vol 28 (08) ◽  
pp. 1950065 ◽  
Author(s):  
Tahani R. Makki ◽  
Mounib F. El Eid ◽  
Grant J. Mathews
Keyword(s):  
Dark Matter ◽  
Early Universe ◽  
Nuclear Physics ◽  
Big Bang ◽  
Light Elements ◽  
Big Bang Nucleosynthesis ◽  
Chemical Potentials ◽  
The Creation ◽  
The Universe

The light elements and their isotopes were produced during standard big bang nucleosynthesis (SBBN) during the first minutes after the creation of the universe. Comparing the calculated abundances of these light species with observed abundances, it appears that all species match very well except for lithium (7Li) which is overproduced by the SBBN. This discrepancy is rather challenging for several reasons to be considered on astrophysical and on nuclear physics ground, or by invoking nonstandard assumptions which are the focus of this paper. In particular, we consider a variation of the chemical potentials of the neutrinos and their temperature. In addition, we investigated the effect of dark matter on 7Li production. We argue that including nonstandard assumptions can lead to a significant reduction of the 7Li abundance compared to that of SBBN. This aspect of lithium production in the early universe may help to resolve the outstanding cosmological lithium problem.

COSMOLOGICAL SOLUTIONS AND THEIR EFFECTIVE PROPERTIES OF MATTER IN KALUZA-KLEIN THEORY

1994 ◽  
Vol 03 (03) ◽  
pp. 627-637 ◽  
Author(s):  
HONGYA LIU ◽  
PAUL S. WESSON
Keyword(s):  
Globular Clusters ◽  
Effective Properties ◽  
Plane Waves ◽  
Big Bang ◽  
Field Equations ◽  
Fifth Dimension ◽  
Cosmological Solutions ◽  
Klein Theory ◽  
The Universe ◽  
Kaluza Klein

We derive a “wave-like” class of exact cosmological solutions of the apparently empty 5D Kaluza-Klein field equations. Here by “wave-like” we mean that the solutions look like plane waves propagating in the fifth dimension. In the interpretation that the fifth dimension in Kaluza-Klein theory may induce matter in four dimensions, we then calculate the effective energy density ρ and pressure p, and study in detail the case for which the equation of state is p=γρ (where γ is an arbitrary constant). We show that for both the matter-dominated (γ=0) and radiation-dominated (γ=1/3) eras of the universe, the 4D spacetime defined by hypersurfaces of the 5D metrics are just the same as those of the standard Friedmann-Robertson-Walker models of general relativity. However, in our models the big bang is like a shock wave propagating along the fifth dimension, and different observers can measure different ages for the universe. This property may be tested using the spread in ages of astrophysical objects such as globular clusters.

scholarly journals Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

2019 ◽  
Vol 485 (3) ◽  
pp. 4311-4329 ◽  
Author(s):  
Christian I Johnson ◽  
Nelson Caldwell ◽  
R Michael Rich ◽  
Mario Mateo ◽  
John I Bailey
Keyword(s):  
Globular Clusters ◽  
First Generation ◽  
Light Element ◽  
Chemical Abundances ◽  
Intermediate Composition ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
Red Giant ◽  
Composition Properties ◽  
Delayed Phase

ABSTRACT NGC 6402 is among the most massive globular clusters in the Galaxy, but little is known about its detailed chemical composition. Therefore, we obtained radial velocities and/or chemical abundances of 11 elements for 41 red giant branch stars using high resolution spectra obtained with the Magellan-M2FS instrument. We find NGC 6402 to be only moderately metal-poor with 〈[Fe/H]〉 = −1.13 dex (σ = 0.05 dex) and to have a mean heliocentric radial velocity of −61.1 km s−1 (σ = 8.5 km s−1). In general, NGC 6402 exhibits mean composition properties that are similar to other inner Galaxy clusters, such as [α/Fe] ∼+0.3 dex, [Cr,Ni/Fe] ∼ 0.0 dex, and 〈[La/Eu]〉 = −0.08 dex. Similarly, we find large star-to-star abundance variations for O, Na, Mg, Al, and Si that are indicative of gas that experienced high temperature proton-capture burning. Interestingly, we not only detect three distinct populations but also find large gaps in the [O/Fe], [Na/Fe], and [Al/Fe] distributions that may provide the first direct evidence of delayed formation for intermediate composition stars. A qualitative enrichment model is discussed where clusters form stars through an early ($\lesssim$5–10 Myr) phase, which results in first generation and ‘extreme’ composition stars, and a delayed phase ($\gtrsim$40 Myr), which results in the dilution of processed and pristine gas and the formation of intermediate composition stars. For NGC 6402, the missing intermediate composition stars suggest the delayed phase terminated prematurely, and as a result the cluster may uniquely preserve details of the chemical enrichment process.

scholarly journals Constant light element abundances suggest that the extended P1 in NGC 2808 is not a consequence of CNO-cycle nucleosynthesis

2019 ◽  
Vol 485 (3) ◽  
pp. 4128-4133 ◽  
Author(s):  
I Cabrera-Ziri ◽  
C Lardo ◽  
A Mucciarelli
Keyword(s):  
Mass Fraction ◽  
Globular Clusters ◽  
Light Element ◽  
Complete Characterization ◽  
Alternative Mechanism ◽  
Abundance Pattern ◽  
Element Abundances ◽  
Chemical Enrichment ◽  
Giant Stars ◽  
Cno Cycle

Abstract Recent photometric results have identified a new population among globular cluster stars. This population, referred to as the ‘extended P1', has been suggested to be the manifestation of a new abundance pattern where the initial mass fraction of He changes among cluster stars that share the same CNO values. The current paradigm for the formation of the multiple stellar populations in globular clusters assumes that variations in He are the product of chemical ‘enrichment’ by the ashes of the CNO-cycle (which changes He and other elements like C, N and O simultaneously). We obtained MIKE@Magellan spectra of six giant stars in NGC 2808, a cluster with one of the strongest examples of the extended P1 population. We provide the first complete characterization of the light elements abundances for the stars along a significant range of the extended P1 photometric group. The stars from our sample appear to be homogeneous in C, N, O, Na, Mg and Al. The lack of a significant change in these products of the CNO-cycle suggests that unlike the rest of the populations identified to date, the photometric changes responsible for the extended P1 feature are a consequence of an alternative mechanism. Our measurements are consistent with the interpretations where the changes of the He mass fraction among these stars could be a consequence of p–p chain nucleosynthesis (which could increase the He in stars without affecting heavier elements). Having said that, direct measurements of He are necessary to conclude if variations of this element are present among extended P1 stars.

On Atomic Diffusion and the Cosmological Lithium Abundance

2013 ◽  
Vol 9 (S298) ◽  
pp. 407-407
Author(s):  
Pieter Gruyters ◽  
Andreas J. Korn ◽  
Paul S. Barklem
Keyword(s):  
Globular Clusters ◽  
Ad Hoc ◽  
Background Radiation ◽  
Big Bang ◽  
Stellar Structure ◽  
Atomic Diffusion ◽  
Green Line ◽  
Microwave Background ◽  
Lithium Abundance ◽  
Microwave Background Radiation

When it comes to lithium in late-type stars, atomic diffusion (AD) refers to the slow gravitational settling below the convective zone. Richard, Michaud & Richter, J. (2005) computed the influence of diffusion on the lithium abundance with different additional mixing (AddMix) parameters, after 13.5 Gyr with an initial Li abundance compatible with BBN. Without AddMix the abundance of lithium would decrease when the temperature of the star increases. This is depicted by the dashed green line in the left panel of Fig. 1 and is in contradiction with the existence of a lithium plateau. But with a model including ad-hoc AddMix, where the AddMix diffusion coefficient is given by DT and is connected to DHe(AD) at a reference temperature of log T0=6.25, it is possible to reproduce the plateau as seen in the figure (solid green line). AD with AddMix has so far been shown to be at work in two globular clusters (GC) with different metallicities. Korn et al. (2007) showed the effects in NGC 6397 at [Fe/H] = −2.1. More recently Gruyters et al. (2013) have shown smaller effects, but similar in nature, in NGC 6752 at [Fe/H] = −1.6. The Li abundance for both clusters can be brought in to agreement with predictions from the cosmic microwave background radiation and Big Bang nucleosynthesis (CMB+BBN) by using stellar structure models including AD and AddMix, although with different efficiencies of AddMix. It seems there is an evolution of AddMix with metallicity which renders AD less efficient. As AddMix acts only in the outer regions, helium settling in the core is not affected, and so the overall evolution (e.g. Teff-age relation) will be similar regardless of this parameter.

Fossils: Microwave Radiation and Light Elements

2020 ◽  
pp. 114-183
Author(s):  
P. J. E. Peebles
Keyword(s):  
Thermal Radiation ◽  
Microwave Radiation ◽  
Mass Density ◽  
Big Bang ◽  
Helium Abundance ◽  
Light Elements ◽  
Expanding Universe ◽  
George Gamow ◽  
Baryon Mass ◽  
The Universe

This chapter focuses on the informative fossils left from a time when the universe was very different from now, dense and hot enough to produce the light elements and the sea of thermal radiation that nearly uniformly fills space. It begins by reviewing the behavior of a sea of microwave radiation in an expanding universe. The chapter then considers how George Gamow and his colleagues, Ralph Alpher and Robert Herman, hit on the main elements of the hot big bang cosmology, including the sea of microwave radiation and the large helium abundance, but failed to capture the interest of the community. It assesses how it came to be seen that the abundance of helium is much larger than expected from production in stars but is readily understood as the result of thermonuclear reactions in the hot big bang cosmology. This attracted little attention prior to the recognition of a second fossil: the sea of microwave radiation. The chapter concludes with the steps to a persuasive measurement of the primeval abundance of deuterium and the implied baryon mass density.

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