scholarly journals Theoretical stellar ΔY/ΔO in the early Universe

2009 ◽  
Vol 5 (S268) ◽  
pp. 447-452
Author(s):  
Sylvia Ekström ◽  
Georges Meynet ◽  
André Maeder ◽  
Cristina Chiappini ◽  
Cyril Georgy ◽  
...  
Keyword(s):  
Early Universe ◽  
Chemical Evolution ◽  
Point Of View ◽  
Theoretical Point ◽  
Chemical Enrichment ◽  
Low Metallicity ◽  
Stellar Models ◽  
Population Iii Stars ◽  
The Universe ◽  
Population Iii

AbstractPopulation III stars initiated the chemical enrichment of the Universe. Chemical evolution models seem to favour fast rotators among the very low-metallicity population. When a star rotates fast, it ejects significant quantities of He and its nucleosynthesic products are modified compared to the case without rotation. The value of ΔY/ΔO is explored from a theoretical point of view through stellar models of zero- or very low-metallicity.

The fifth force: An enigma in this Universe

2019 ◽  
Vol 34 (09) ◽  
pp. 1950056 ◽  
Author(s):  
Koijam Manihar Singh ◽  
Kangujam Priyokumar Singh
Keyword(s):  
Theoretical Calculations ◽  
Point Of View ◽  
Theoretical Point ◽  
Experimental Proof ◽  
Fifth Force ◽  
Theory Of Everything ◽  
Discovery Science ◽  
Near Future ◽  
The Universe ◽  
High Hope

In an attempt to explain some of the unknown phenomena of nature, including dark energy and dark matter, we explore the possibility of the existence of a fifth fundamental force of nature as also cited by some researchers. With the inclusion of such a force in the system, some of the vague things can be explained and there is high hope of its importance in building up a “theory of everything”. With this intention, we investigate some manifestations of the fifth force which stand from theoretical calculations or from theoretical point of view, though till now there is less experimental proof. However, the theoretical results obtained indicate the existence of a fifth force which will lead to the completion in defining the laws of physics and nature. With this discovery, science may be able to explain the whole complexity of the Universe in near future.

scholarly journals M31 Globular Cluster Metallicities and Ages

2002 ◽  
Vol 207 ◽  
pp. 58-61
Author(s):  
Pauline Barmby
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Globular Cluster ◽  
Chemical Enrichment ◽  
Detailed Explanation ◽  
Age Gap ◽  
Small Delay ◽  
Age Of The Universe ◽  
Lower Limits ◽  
The Universe

Globular cluster ages are more than just lower limits to the age of the universe; the distribution of ages constraints the timescales for galaxy formation and chemical evolution. Globular cluster populations with different metallicities have now been detected in many galaxies, and understanding how these populations formed requires knowing their relative ages. We examined the relative ages of the two M31 globular cluster populations using their color and luminosity distributions and found that the metal-rich clusters could be up to 50% younger than the metal-poor clusters. While a small delay in the formation of metal-rich clusters might be imposed by chemical enrichment timescales, a large age gap demands a more detailed explanation. I outline several possibilities and their promises and problems.

scholarly journals Discovery of the first heavily obscured QSO candidate at z > 6 in a close galaxy pair

2019 ◽  
Vol 628 ◽  
pp. L6 ◽  
Author(s):  
F. Vito ◽  
W. N. Brandt ◽  
F. E. Bauer ◽  
R. Gilli ◽  
B. Luo ◽  
...  
Keyword(s):  
Black Holes ◽  
Early Universe ◽  
Column Density ◽  
Early Growth ◽  
Point Of View ◽  
X Ray ◽  
Confidence Levels ◽  
The Universe ◽  
Companion Galaxy

While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting z >  6 quasars (QSOs) are strongly biased against obscured QSOs, thus considerably limiting our understanding of accreting SMBHs during the first gigayear of the Universe from an observational point of view. We report the Chandra discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close (≈5 kpc) galaxy pair at z = 6.515. One of the members is an optically classified type-1 QSO, PSO167–13. The companion galaxy was first detected as a [C II] emitter by Atacama large millimeter array (ALMA). An X-ray source is significantly (P = 0.9996) detected by Chandra in the 2–5 keV band, with < 1.14 net counts in the 0.5–2 keV band, although the current positional uncertainty does not allow a conclusive association with either PSO167–13 or its companion galaxy. From X-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of NH >  2 × 1024 cm−2 and NH >  6 × 1023 cm−2 at 68% and 90% confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at z >  6.

scholarly journals Constraints on the variations of fundamental couplings by stellar models

2009 ◽  
Vol 5 (H15) ◽  
pp. 306-306
Author(s):  
A. Coc ◽  
S. Ekström ◽  
P. Descouvemont ◽  
E. Vangioni
Keyword(s):  
Fundamental Constants ◽  
Helium Burning ◽  
Star Models ◽  
Triple Alpha ◽  
Stellar Models ◽  
Population Iii Stars ◽  
Population Iii

AbstractThe effect of variations of the fundamental constants on the thermonuclear rate of the triple alpha reaction, 4He(αα,γ)12C, that bridges the gap between 4He and 12C is investigated. We follow the evolution of 15 and 60 M⊙ zero metallicity star models, up to the end of core helium burning. They are assumed to be representative of the first, Population III stars undergoing a very peculiar evolution due to the absence of initial CNO elements (zero metallicity). The calculated oxygen and carbon abundances resulting from helium burning can then be used to constrain the variations of the fundamental constants.

scholarly journals Extragalactic planetary nebulae: Tracers of the chemical evolution of nearby galaxies

2011 ◽  
Vol 7 (S283) ◽  
pp. 251-258 ◽  
Author(s):  
Laura Magrini ◽  
Letizia Stanghellini ◽  
Denise R. Gonçalves
Keyword(s):  
Chemical Evolution ◽  
Stellar Evolution ◽  
Planetary Nebulae ◽  
Spectroscopic Studies ◽  
Disk Galaxies ◽  
Chemical Enrichment ◽  
History Of ◽  
External Galaxies ◽  
Low Metallicity ◽  
Nearby Galaxies

AbstractThe study of the chemical composition of Planetary Nebulae in external galaxies is of paramount importance for the fields of stellar evolution and chemical enrichment history of galaxies. In recent years a number of spectroscopic studies with 6-8m-class telescopes have been devoted to this subject improving our knowledge of, among other, the time-evolution of the radial metallicity gradient in disk galaxies, the chemical evolution of dwarf galaxies, and stellar evolution at low metallicity.

scholarly journals The effects of Population III stars and variable IMF on the chemical evolution of the Galaxy

New Astronomy ◽  
2006 ◽  
Vol 11 (4) ◽  
pp. 306-324 ◽  
Author(s):  
Silvia Kuna Ballero ◽  
Francesca Matteucci ◽  
Cristina Chiappini
Keyword(s):  
Chemical Evolution ◽  
The Galaxy ◽  
Population Iii Stars ◽  
Population Iii

scholarly journals Stellar spectra analysis of giant stars: ARCTURUS

2020 ◽  
pp. 347-348
Author(s):  
Maria Rah
Keyword(s):  
High Resolution ◽  
Early Universe ◽  
Chemical Evolution ◽  
The Other ◽  
High Resolution Spectroscopy ◽  
Spectra Analysis ◽  
Stellar Spectra ◽  
Giant Stars ◽  
Low Metallicity ◽  
Red Giant

In this study, we analyzed the evolved red giant ARCTURUS using high-resolution spectroscopy that was taken by HARPS. The other names of this star is α Boo - Arcturus - HR 5340 - HD 124897 - HIP 69673. This evolved (log g = 1.66 dex) star shows low metallicity nature ([Fe/H] = -0.52), which could be employed to study the chemical evolution of the early universe.

scholarly journals The stochastic enrichment of Population II stars

2020 ◽  
Vol 500 (4) ◽  
pp. 5214-5228
Author(s):  
Louise Welsh ◽  
Ryan Cooke ◽  
Michele Fumagalli
Keyword(s):  
First Generation ◽  
Milky Way ◽  
Systematic Errors ◽  
Chemical Abundances ◽  
Chemical Enrichment ◽  
Halo Stars ◽  
Chemical Products ◽  
Population Iii Stars ◽  
Intrinsic Scatter ◽  
Population Iii

ABSTRACT We investigate the intrinsic scatter in the chemical abundances of a sample of metal-poor ([Fe/H] &lt; −2.5) Milky Way halo stars. We draw our sample from four historic surveys and focus our attention on the stellar Mg, Ca, Ni, and Fe abundances. Using these elements, we investigate the chemical enrichment of these metal-poor stars using a model of stochastic chemical enrichment. Assuming that these stars have been enriched by the first generation of massive metal-free stars, we consider the mass distribution of the enriching population alongside the stellar mixing and explosion energy of their supernovae. For our choice of stellar yields, our model suggests that the most metal-poor stars were enriched, on average, by $\hat{N}_{\star }=5^{+13}_{-3}~(1\sigma)$ Population III stars. This is comparable to the number of enriching stars inferred for the most metal-poor DLAs. Our analysis therefore suggests that some of the lowest mass structures at z ∼ 3 contain the chemical products from &lt; 13(2σ) Population III enriched minihaloes. The inferred IMF is consistent with that of a Salpeter distribution and there is a preference towards ejecta from minimally mixed hypernovae. However, the estimated enrichment model is sensitive to small changes in the stellar sample. An offset of ∼ 0.1 dex in the [Mg/Ca] abundance is shown to be sensitive to the inferred number of enriching stars. We suggest that this method has the potential to constrain the multiplicity of the first generation of stars, but this will require: (1) a stellar sample whose systematic errors are well understood; and, (2) documented uncertainties associated with nucleosynthetic yields.

scholarly journals The first galactic stars and chemical enrichment in the halo

2009 ◽  
Vol 5 (S265) ◽  
pp. 81-89
Author(s):  
Piercarlo Bonifacio
Keyword(s):  
Chemical Composition ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
Low Metallicity ◽  
Low Mass ◽  
Indirect Information ◽  
The Universe

AbstractThe cosmic microwave background and the cosmic expansion can be interpreted as evidence that the Universe underwent an extremely hot and dense phase about 14 Gyr ago. The nucleosynthesis computations tell us that the Universe emerged from this state with a very simple chemical composition: H, 2H, 3He, 4He, and traces of 7Li. All other nuclei where synthesised at later times. Our stellar evolution models tell us that, if a low-mass star with this composition had been created (a “zero-metal” star) at that time, it would still be shining on the Main Sequence today. Over the last 40 years there have been many efforts to detect such primordial stars but none has so-far been found. The lowest metallicity stars known have a metal content, Z, which is of the order of 10−4Z⊙. These are also the lowest metallicity objects known in the Universe. This seems to support the theories of star formation which predict that only high mass stars could form with a primordial composition and require a minimum metallicity to allow the formation of low-mass stars. Yet, since absence of evidence is not evidence of absence, we cannot exclude the existence of such low-mass zero-metal stars, at present. If we have not found the first Galactic stars, as a by product of our searches we have found their direct descendants, stars of extremely low metallicity (Z ≤ 10−3Z⊙). The chemical composition of such stars contains indirect information on the nature of the stars responsible for the nucleosynthesis of the metals. Such a fossil record allows us a glimpse of the Galaxy at a look-back time equivalent to redshift z = 10, or larger. The last ten years have been full of exciting discoveries in this field, which I will try to review in this contribution.

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