scholarly journals Theoretical Predictions of Surface Light Element Abundances in Protostellar and Pre-Main Sequence Phase

2021 ◽  
Vol 8 ◽  
Author(s):  
E. Tognelli ◽  
S. Degl’Innocenti ◽  
P. G. Prada Moroni ◽  
L. Lamia ◽  
R. G. Pizzone ◽  
...  
Keyword(s):  
Cross Sections ◽  
Main Sequence ◽  
Light Element ◽  
Element Abundance ◽  
Light Elements ◽  
Convective Envelope ◽  
Stellar Envelope ◽  
Element Abundances ◽  
Stellar Interior ◽  
Theoretical Predictions

Theoretical prediction of surface stellar abundances of light elements–lithium, beryllium, and boron–represents one of the most interesting open problems in astrophysics. As well known, several measurements of 7Li abundances in stellar atmospheres point out a disagreement between predictions and observations in different stellar evolutionary phases, rising doubts about the capability of present stellar models to precisely reproduce stellar envelope characteristics. The problem takes different aspects in the various evolutionary phases; the present analysis is restricted to protostellar and pre-Main Sequence phases. Light elements are burned at relatively low temperatures (T from ≈2 to ≈5 million degrees) and thus in the early evolutionary stages of a star they are gradually destroyed at different depths of stellar interior mainly by (p, α) burning reactions, in dependence on the stellar mass. Their surface abundances are strongly influenced by the nuclear cross sections, as well as by the extension toward the stellar interior of the convective envelope and by the temperature at its bottom, which depend on the characteristics of the star (mass and chemical composition) as well as on the energy transport in the convective stellar envelope. In recent years, a great effort has been made to improve the precision of light element burning cross sections. However, theoretical predictions surface light element abundance are challenging because they are also influenced by the uncertainties in the input physics adopted in the calculations as well as the efficiency of several standard and non-standard physical processes active in young stars (i.e. diffusion, radiative levitation, magnetic fields, rotation). Moreover, it is still not completely clear how much the previous protostellar evolution affects the pre-Main Sequence characteristics and thus the light element depletion. This paper presents the state-of-the-art of theoretical predictions for protostars and pre-Main Sequence stars and their light element surface abundances, discussing the role of (p, α) nuclear reaction rates and other input physics on the stellar evolution and on the temporal evolution of the predicted surface abundances.

scholarly journals The light elements in a helio- and asteroseismic perspective

2009 ◽  
Vol 5 (S268) ◽  
pp. 387-394
Author(s):  
Sylvie Vauclair
Keyword(s):  
Main Sequence ◽  
Light Element ◽  
Heavy Elements ◽  
Light Elements ◽  
Main Sequence Stars ◽  
General Introduction ◽  
Helium Content ◽  
Element Abundances ◽  
The Past

AbstractAsteroseismology is a powerful tool to derive stellar parameters, including the helium content and internal helium gradients, and the macroscopic motions which can lead to lithium, beryllium, and boron abundance variations. Precise determinations of these parameters need deep analyses for each individual stars. After a general introduction on helio and asteroseismology, I first discuss the solar case, the results which have been obtained in the past two decades, and the crisis induced by the new determination of the abundances of heavy elements. Then I discuss asteroseismology in relation with light element abundances, especially for the case of main sequence stars.

scholarly journals Light element abundance inhomogeneities in globular clusters: probing star formation and evolution in the early Milky Way

1994 ◽  
Vol 72 (11-12) ◽  
pp. 772-781 ◽  
Author(s):  
Michael M. Briley ◽  
Roger A. Bell ◽  
James E. Hesser ◽  
Graeme H. Smith
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Main Sequence ◽  
Light Element ◽  
Star Formation History ◽  
Element Abundance ◽  
Chemical Compositions ◽  
Original Material ◽  
Abundance Patterns ◽  
Red Giant

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the nature of the observed distribution of these elements is key to constraining protogalactic star formation history. Patterns deduced from low-resolution spectroscopy of the CN, CH, NH, and CO molecules for low-mass stars in their core-hydrogen or first shell-hydrogen burning phases in the oldest ensembles known, the Galactic globular star clusters, are reviewed. New results for faint stars in NGC 104 (47 Tuc, C0021-723) reveal that the bimodal, anticorrelated pattern of CN and CH strengths found among luminous evolved stars is also present in stars nearing the end of their main-sequence lifetimes. In the absence of known mechanisms to mix newly synthesized elements from the interior to the observable surface layers of such unevolved stars, those particular inhomogeneities imply that the original material from which the stars formed some 15 billion years ago was chemically inhomogeneous in the C and N elements. However, in other clusters, observations of abundance ratios and C isotope ratios suggest that alterations to surface chemical compositions are produced as stars evolve from the main sequence through the red giant branch. Thus, the current observed distributions of C, N, and O among the brightest stars (those also observed most often) may not reflect the true distribution from which the protocluster cloud formed. The picture that is emerging of the C, N, and O abundance patterns within globular clusters may be one which requires a complicated combination of stellar evolutionary and primordial effects for its explanation.

scholarly journals Constraints from the cosmic microwave background experiments

2009 ◽  
Vol 5 (S268) ◽  
pp. 17-17
Author(s):  
Joanna Dunkley
Keyword(s):  
Cosmic Microwave Background ◽  
Light Element ◽  
Baryon Density ◽  
Light Elements ◽  
Microwave Background ◽  
Element Abundances

AbstractI will give a review of the current constrains on light element abundances from cosmic microwave background experiments, focusing on results from WMAP and discussing prospects from upcoming data from Planck and ground-based experiments. I will describe how the production of light elements affects the CMB anisotropies, and how we use the data to extract cosmological information that includes constraints on the baryon density, and primordial abundances.

scholarly journals Ages and chemical compositions of massive clusters in NGC147 and M31

2015 ◽  
Vol 12 (S316) ◽  
pp. 347-348
Author(s):  
Margarita Sharina ◽  
Vladislav Shimansky
Keyword(s):  
Globular Clusters ◽  
Light Element ◽  
Mass Function ◽  
Stellar Atmospheres ◽  
Element Abundance ◽  
Chemical Compositions ◽  
Element Abundances ◽  
Light Spectra ◽  
Medium Resolution ◽  
Red Giant

AbstractWe present estimates of ages, [Fe/H], helium content (Y) and abundances of C, N, Mg, Ca, and several other elements for the following globular clusters (GCs): GC7 in NGC147, and Mayall II, Mackey 1 and Mackey 6 in M31. Medium-resolution integrated-light spectra of the GCs were conducted with the 6m telescope. To derive the ages and abundances for the GCs we carried out their population synthesis using model stellar atmospheres, the Padova YZVAR isochrones and the Chabrier mass function. We compare the results with the corresponding data obtained using the same method for several massive Galactic GCs. We show that the differences in the light-element abundances between GCs with similar ages and metallicities may reach 0.5-0.6 dex. The corresponding differences for other elements are usually 2-3 times smaller. We suggest that at least partially the detected differences may be due to light-element abundance variations in the atmospheres of high-luminosity red giant branch stars as a consequence of the transportation of the produced elements to the surface layers.

scholarly journals Light elements in stars with exoplanets

2009 ◽  
Vol 5 (S268) ◽  
pp. 291-299
Author(s):  
N. C. Santos ◽  
E. Delgado Mena ◽  
G. Israelian ◽  
J. I. González-Hernández ◽  
M. C. Gálvez-Ortiz ◽  
...  
Keyword(s):  
Present Status ◽  
Light Element ◽  
Giant Planets ◽  
Heavy Elements ◽  
Average Field ◽  
Light Elements ◽  
Element Abundances

AbstractIt is well known that stars orbited by giant planets have higher abundances of heavy elements when compared with average field dwarfs. A number of studies have also addressed the possibility that light element abundances are different in these stars. In this paper we will review the present status of these studies. The most significant trends will be discussed.

scholarly journals Experimental Nuclear Astrophysics With the Light Elements Li, Be and B: A Review

2021 ◽  
Vol 7 ◽  
Author(s):  
G.G. Rapisarda ◽  
L. Lamia ◽  
A. Caciolli ◽  
Chengbo Li ◽  
S. Degl’Innocenti ◽  
...  
Keyword(s):  
Reaction Rate ◽  
Main Sequence ◽  
Light Element ◽  
Reaction Rates ◽  
Big Bang ◽  
Trojan Horse ◽  
Electron Screening ◽  
Activation Technique ◽  
Light Elements ◽  
Trojan Horse Method

Light elements offer a unique opportunity for studying several astrophysical scenarios from Big Bang Nucleosynthesis to stellar physics. Understanding the stellar abundances of light elements is key to obtaining information on internal stellar structures and mixing phenomena in different evolutionary phases, such as the pre-main-sequence, main-sequence or red-giant branch. In such a case, light elements, i.e., lithium, beryllium and boron, are usually burnt at temperatures of the order of 2–5 × 106 K. Consequently, the astrophysical S(E)-factor and the reaction rate of the nuclear reactions responsible for the burning of such elements must be measured and evaluated at ultra-low energies (between 0 and 10 keV). The Trojan Horse Method (THM) is an experimental technique that allows us to perform this kind of measurements avoiding uncertainties due to the extrapolation and electron screening effects on direct data. A long Trojan Horse Method research program has been devoted to the measurement of light element burning cross sections at astrophysical energies. In addition, dedicated direct measurements have been performed using both in-beam spectroscopy and the activation technique. In this review we will report the details of these experimental measurements and the results in terms of S(E)-factor, reaction rate and electron screening potential. A comparison between astrophysical reaction rates evaluated here and the literature will also be given.

scholarly journals Microanalysis of Light Elements with an Ultrathin Window X-Ray Spectrometer

1980 ◽  
Vol 38 ◽  
pp. 90-93
Author(s):  
L. E. Thomas
Keyword(s):  
Cross Sections ◽  
Light Element ◽  
Light Elements ◽  
X Ray ◽  
Electron Energy Loss Spectrometry ◽  
Ionization Cross Sections ◽  
Low X ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

Compared to electron energy loss spectrometry (ELS), energy-dispersive X-ray (EDX) spectrometry at first appears inefficient for microanalysis of light elements. K-shell ionization cross sections increase rapidly at low atomic numbers, as shown in Figure 1, while the corresponding X-ray yields remain about constant. Also, the efficiency of the EDX detector decreases at low X-ray energies (Figure 2) due to X-ray absorption in its inactive outer layers and protective window. Even if the window is eliminated, these considerations clearly favor ELS for detection of small, light element masses.

scholarly journals Measurements of the differential cross sections of the production of Z + jets and γ + jets and of Z boson emission collinear with a jet in pp collisions at $$ \sqrt{s} $$ = 13 TeV

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
◽  
A. M. Sirunyan ◽  
A. Tumasyan ◽  
W. Adam ◽  
F. Ambrogi ◽  
...  
Keyword(s):  
Cross Sections ◽  
Differential Cross ◽  
Z Boson ◽  
Center Of Mass ◽  
Z Bosons ◽  
Differential Cross Sections ◽  
Pp Collisions ◽  
Center Of Mass Energy ◽  
Cms Experiment ◽  
Theoretical Predictions

Abstract Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet.

scholarly journals Experimental study of the $ \gamma p \rightarrow K^{0}\Sigma^{+}$, $ \gamma n \rightarrow K^{0} \Lambda$, and $ \gamma n \rightarrow K^{0} \Sigma^{0}$ reactions at the Mainz Microtron

2019 ◽  
Vol 55 (11) ◽  
Author(s):  
C. S. Akondi ◽  
K. Bantawa ◽  
D. M. Manley ◽  
S. Abt ◽  
P. Achenbach ◽  
...  
Keyword(s):  
Experimental Study ◽  
Cross Sections ◽  
Differential Cross ◽  
Legendre Polynomials ◽  
Neutral Kaon ◽  
Experimental Results ◽  
Differential Cross Sections ◽  
Theoretical Predictions ◽  
Photoproduction Reactions ◽  
Insight Into

Abstract.This work measured $ \mathrm{d}\sigma/\mathrm{d}\Omega$dσ/dΩ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $ \gamma p\rightarrow K^0\Sigma^+$γp→K0Σ+, $ \gamma n\rightarrow K^0\Lambda$γn→K0Λ, and $ \gamma n\rightarrow K^0 \Sigma^0$γn→K0Σ0 reactions. Our results for $ \gamma n\rightarrow K^0 \Sigma^0$γn→K0Σ0 are the first-ever measurements for that reaction. These data will provide insight into the properties of $ N^{\ast}$N* resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $ \pi N$πN channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.

scholarly journals Non-Adiabatic Seismic Study of The Thin Convective Envelope of δ Scuti Stars

2004 ◽  
Vol 193 ◽  
pp. 470-473
Author(s):  
M.-A. Dupret ◽  
A. Grigahcène ◽  
R. Garrido ◽  
J. Montalban ◽  
M. Gabriel ◽  
...  
Keyword(s):  
Instability Strip ◽  
Full Spectrum ◽  
Convective Envelope ◽  
Theoretical Predictions ◽  
Mode Stability ◽  
Different Color ◽  
Mixing Length Theory ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Phase Differences

AbstractFor δ Sct stars, the theoretical predictions of a non-adiabatic pulsation code are very dependent on the characteristics of the thin convective envelope of the models (Balona & Evers 1999). The treatment of the non-adiabatic interaction between convection and pulsation also has a significant impact on the results, particularly near the red edge of the instability strip. The non-adiabatic theoretical predictions can be tested upon observations by comparing them to the amplitude ratios and phase differences as observed in different color passbands (Dupret et al. 2003). In the first part of this paper, we compare the results obtained by adopting different treatments of convection in the interior and atmosphere models: mixing-length theory (MLT) and full spectrum of turbulence (FST) (Canuto et al. 1996, CGM). In the second part, we examine the problem of the interaction between convection and pulsation and compare the mode stability obtained with and without including time-dependent convection in our non-adiabatic code.

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