Effects of possible deviations of fundamental physical constants on primordial nucleosynthesis

We study the effects of possible deviations of fundamental physical constants on the yields of light nuclides, ²D, ³He, ⁴He, ⁷Li, and others during primordial nucleosynthesis. The deviations of fundamental constants from their current values are considered in the low-energy approximation of string theories; the latter predict the existence of a scalar field, which, apart from the tensor gravitational field, determines the space geometry. A two-parameter (η, δ) model is constructed for primordial nucleosynthesis: η = n _B /n _γ is the baryon-to-photon density ratio, and Ω is the relative deviation of fundamental physical constants at the epoch of primordial nucleosynthesis from their current values. A dependence of η on the deviation of coupling constants Ω has been derived on condition that the primordial helium abundance is Y _p = f(η, δ) = const, where const corresponds to experimental values. We thus showed that the relative baryonic density (and hence Ω_B could vary over a much wider range than allowed by the standard nucleosynthesis model. Considering this result, we discuss the recently found mismatch between Ω_B obtained from an analysis of CMBR anisotropy and from the standard primordial nucleosynthesis model.     

Deuterium, lithium and the density of the Universe

The main outcome of the primordial nucleosynthesis is the ability to account for the abundances of D, ³He, ⁴He and ⁷Li with the proper choice of the nuclear density parameter ω_B. The relative advantages/disadvantages of D and ⁷Li as the proper `baryometer' are discussed. In favour of D, the main arguments are the relative simplicity of the formation/destruction schema, but this is challenged by the large uncertainties on the choice of its actual `primordial' abundance and on the galactic evolution scheme. In favour of ⁷Li there are the confirmation of the so called `Spite plateau' and the observation of ⁶Li at the surface of at least one (may be two) Population II stars, but the paucity of such stars such as the possibility of scenarios in which the ⁷Li abundance could be affected even in these stars cannot be overlooked. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pregalactic 4He abundance with new data on systematic errors in its determination

Primordial helium abundance in the universe was determined based on spectral observations of low-metallicity blue compact dwarf galaxies. The intensities of the observed emission lines were corrected for several mechanisms, including stellar absorption and collisional excitation of the helium and hydrogen emission spectra. Parameters that were necessary for correcting the deviations of the emission lines?? intensities from their recombination values were determined using the Monte Carlo method. The obtained value of primordial helium of 0.2557 ± 0.0014 is higher by 3% than the value obtained from the analysis of the microwave background radiation fluctuations under the assumption of the standard model of primordial nucleosynthesis. This points to the existence of new types of neutrino in the primordial nucleosynthesis epoch, in addition to the three known ones.     

On the APM power spectrum and the CMB anisotropy: evidence for a phase transition during inflation?

Adams et al. have noted that according to our current understanding of the unification of fundamental interactions, there should have been phase transitions associated with spontaneous symmetry breaking during the inflationary era. This may have resulted in the breaking of scale-invariance of the primordial density perturbation for brief periods. A possible such feature was identified in the power spectrum of galaxy clustering in the automated plate measurement (APM) survey at the scale k  ∼ 0.1  h  Mpc ^− 1 and it was shown that the secondary acoustic peaks in the power spectrum of the cosmic microwave background (CMB) anisotropy should consequently be suppressed. We demonstrate that this prediction is confirmed by the recent Boomerang and Maxima observations, which favour a step-like spectral feature in the range k  ∼ (0.06–0.6)  h  Mpc ^− 1 , independently of the similar previous indication from the APM data. Such a spectral break enables an excellent fit to both APM and CMB data with a baryon density consistent with the big bang nucleosynthesis (BBN) value. It also allows the possibility of a matter-dominated universe with zero cosmological constant, which we show can now account for even the evolution of the abundance of rich clusters.     

The galactic evolution of lithium

Measurements of lithium in stars of different galactic populations such as young open clusters ( Per, Pleiades, Praesepe, Coma, Hyades), very young stellar associations (Taurus-Auriga, Chamaeleon, Ophiuchus clouds), intermediate and old open clusters (NGC 752, M 67, NGC 188), old disc stars and halo stars give us the observational framework from which the galactic evolution of lithium has to be inferred. This element is produced mainly via three mechanisms: primordial nucleosynthesis, spallation reactions in the interstellar medium and thermonuclear reactions in some particular stellar evolutionary stages (novae, red giants). The complicated nucleosynthesis and the fact that astration of lithium in stars is not well understood, makes a direct interpretation of the lithium evolutionary abundance curve difficult. The constraints set by recent lithium measurements in very old open clusters and metal-deficient stars on galactic lithium production mechanisms are discussed. Current problems in the determination of the primordial lithium abundance are briefly reviewed.     

A Theoretical Light-Curve Model for the 1999 Outburst of U Scorpii

We report the detection of the Pb i lambda4057.8 line in the very metal-poor (&sqbl0;Fe&solm0;H&sqbr0;=-2.7), carbon-rich star, LP 625-44. We determine the abundance of Pb (&sqbl0;Pb&solm0;Fe&sqbr0;=2.65) and 15 other neutron-capture elements. The abundance pattern between Ba and Pb agrees well with a scaled solar system s-process component, while the lighter elements (Sr-Zr) are less abundant than Ba. The enhancement of s-process elements is interpreted as a result of mass transfer in a binary system from a previous asymptotic giant branch (AGB) companion, an interpretation strongly supported by radial velocity variations of this system. The detection of Pb makes it possible, for the first time, to compare model predictions of s-process nucleosynthesis in AGB stars with observations of elements between Sr and Pb. The Pb abundance is significantly lower than the prediction of recent models (e.g., Gallino et al.), which succeeded in explaining the metallicity dependence of the abundance ratios of light s-elements (Sr-Zr) to heavy ones (Ba-Dy) found in previously observed s-process-enhanced stars. This suggests that one should either (1) reconsider the underlying assumptions concerning the (13)C-rich s-processing site ((13)C pocket) in the present models or (2) investigate alternative sites of s-process nucleosynthesis in very metal-poor AGB stars.     

Lithium Abundance of Metal－poor Stars

High-resolution, high signal-to-noise ratio spectra have been obtained for 32 metal-poor stars. The equivalent widths of Li A6708 A were measured and the lithium abundances were derived. The average lithium abundance of 21 stars on the lithium plateau is 2.33±0.02 dex. The Lithium plateau exhibits a marginal trend along metallicity, dA(Li)/d[Fe/H] ?0.12±0.06, and no clear trend with the effective temperature. The trend indicates that the abundance of lithium plateau may not be primordial and that a part of the lithium was produced in Galactic Chemical Evolution (GCE).     

HELIOSPHERIC EVOLUTION OF THE HELIUM ISOTOPES

The isotopic ratio of ³He/⁴He, which is routinely measured in the solar wind, on meteorites and in different astrophysical environments, is confined to several times 10^-4. However, in impulsive solar flares this ratio reaches often values larger than unity. The evolution of this ratio from the primordial nucleosynthesis to the present solar conditions is sketched and the resonant plasma effects which enhance spectacularly the abundance of ³He in the impulsive solar flares are described.     

Time of primordial <Superscript>7</Superscript>Be conversion into <Superscript>7</Superscript>Li,energy release and doublet of narrow cosmological neutrino lines

One of the light elements created during the big bang nucleosynthesis is ⁷Be which then decays to ⁷Li by electron capture when recombination becomes effective but well before the Saha equilibrium recombination is reached. This means that ⁷Be should wait until its recombination epoch even though the half-life of the hydrogenic beryllium atom is only 106.4 days. We calculate when the conversion from primordial ⁷Be to ⁷Li occurs taking into account the population of the hyperfine structure sublevels and solving the kinetic equations for recombination, photoionization and conversion rate. We also calculate the energies and the spectrum of two narrow neutrino lines from ⁷Be decay.     

Helium in stellar atmospheres

Helium, which was first discovered on the sun with the help of spectral analysis, plays, together with hydrogen, a principal role in astrophysics. We consider here two fundamental quantities: primordial helium abundance formed during Big Bang nucleosynthesis and the current initial helium abundances in nearby stars. It is shown that stellar atmospheres are enriched in helium during the main-sequence stage. Observational evidence for helium contamination in close OB-binaries is discussed. Stars with strong abundance anomalies are considered, such as chemically peculiar Ap and Bp helium-deficient stars and some types of objects with helium atmospheres.     

Cosmic Lithium-Beryllium-Boron Story

Light element nucleosynthesis is an important chapter of nuclear astrophysics. Specifically, the rare and fragile light nuclei Lithium, Beryllium and Boron (LiBeB) are not generated in the normal course of stellar nucleosynthesis (except ⁷Li) and are, in fact, destroyed in stellar interiors. This characteristic is reflected in the low abundance of these simple species. Up to recently, the most plausible interpretation was that Galactic Cosmic Rays (GCR) interact with interstellar CNO to form LiBeB. Other origins have been also identified: primordial and stellar (⁷Li) and supernova neutrino spallation (⁷Li and ¹¹B). In contrast, ⁹Be, ¹⁰B and ⁶Li are pure spallative products. This last isotope presents a special interest since the ⁶Li/⁷Li ratio has been measured recently in a few halo stars offering a new constraint on the early galactic evolution of light elements. Optical measurements of the beryllium and boron abundances in halo stars have been achieved by the 10 meter KECK telescope and the Hubble Space Telescope. These observations indicate a quasi linear correlation between Be and B vs Fe, at least at low metallicity, which, at first sight, is contradictory to a dominating GCR origin of the light elements which predicts a quadratic relationship. As a consequence, the theory of the origin and evolution of LiBeB nuclei has to be refined. Aside GCRs, which are accelerated in the general interstellar medium (ISM) and create LiBeB through the break up of CNO by fast protons and alphas, Wolf-Rayet stars (WR) and core collapse supernovae (SNII) grouped in superbubbles could produce copious amounts of light elements via the fragmentation in flight of rapid carbon and oxygen nuclei colliding with H and He in the ISM. In this case, LiBeB would be produced independently of the interstellar medium chemical composition and thus a primary origin is expected. These different processes are discussed in the framework of a galactic evolutionary model. More spectroscopic observations (specifically of O, Fe, Li, Be, B) in halo stars are required for a better understanding of the relative contribution of the various mechanisms. Future tests on the injection and acceleration of nuclei by supernovae and Wolf Rayet relying on gamma-ray line astronomy will be invoked in the perspective of the European INTEGRAL satellite. This revised version was published online in July 2006 with corrections to the Cover Date.     

贫金属星r过程核合成相关问题的研究进展

快中子俘获过程(r过程)可以解释大约一半比铁重的稳定(和一些长寿命放射性的)富中子核素的产生,这已经被太阳系及各种金属丰度下恒星的观测结果所证实.为建立r过程模型,需要大量的核物理信息:涉及到β稳定谷与中子滴线之间的各种核素的稳定特性及β衰变分支等物理参数,实验和理论都面临巨大的挑战.综述了近年来贫金属星r过程核合成理...     

Lithium in black hole binaries: the case of X-ray Nova Muscae 1991

We report the detection of the LiI λ6708 resonance line in the K4V secondary of the black-hole binary Nova Muscae 1991. The LiI feature changes with orbital phase, being stronger (EW ∼ 400 mÅ) around φ = 0.0 (observing the dark side of the secondary) and weaker (EW ≤ 190 mÅ) around φ = 0.5 (observing the side facing the compact object). This effect is interpreted as LiI ionization induced by UV/X-ray illumination of the inner hemisphere of the companion star. From the strength of the LiI feature observed around φ = 0.0 we infer a photospheric lithium abundance of logN(Li) ∼ 3. This value should be considered in fact as a lower limit to the true Li abundance because we have not fully corrected for the LiI overionization expected from UV/X-ray illumination.High lithium abundances are becoming a common feature in the secondaries of black hole binaries. After the Li detections in V404 Cyg, A0620-00 and GS2000 + 25, our observations of Nova Muscae not only add a new case to the list, but also demonstrate the impact of irradiation on the formation of the LiI line for the first time. The LiI features observed in the other black hole binaries are probably also affected by irradiation, although not as strongly as in Nova Muscae, and their Li abundances are higher than previously thought.The most attractive scenario for explaining the origin of the high Li abundances in black hole binaries appears to be nucleosynthesis during the explosive accretion events that characterize these objects. We argue that our LiI detection in the secondary of X-ray Nova Muscae 1991, and the transient γ-ray narrow emission feature at 476 keV observed during the 1991 outburst, are both signatures of Li production around the black hole. We propose that the γ-ray emission line was due to ⁷Be electron capture which yielded excited ⁷Li atoms. This reaction is able to account for the central energy, narrow width and time scale of the observed γ-ray emission feature. The presence of Li on the surface of the secondary shows that Li atoms created during the outburst can escape and enrich the interstellar medium.Shrinivas Kulkarni     

富锂巨星研究概述

锂(Li)元素最初诞生于大爆炸核合成,是最重要的轻元素之一.但锂元素丰度在很多类天体中均表现出观测与理论不符的现象,这一问题困扰了天体物理学家数十年.富锂巨星就是这样的一类天体,它们大气中的Li丰度超过了标准恒星演化模型的理论值.虽然富锂巨星早在约四十年前就被发现,但其起源依然是未解之谜.随着以郭守敬望远镜(LAMOST)巡天等为代表的大型光谱巡天项目的开展、以开普勒(Kepler)卫星为代表的星震学观测数据的产出以及数据驱动类方法和技术的飞速发展,针对富锂巨星的研究取得了一系列重要的突破.在此将回顾富锂巨星近四十年来的研究进展,并总结对于富锂巨星最新的认知.     

A Review to the Studies of Lithium-Rich Giants

Lithium (Li) is one of the most important light elements that was primordially synthesized in the Big Bang Nucleosynthesis (BBN). It is also an element that confused astrophysicists for decades, as its observed abundance often contradicts with the theoretical prediction in many different types of celestial objects. Li-rich giant stars are such objects. Their atmospheres contain anomaly high Li abundance than that expected by the standard stellar evolution model. Although the first Li-rich giant star was discovered almost 40 years ago, their origin is still being debated. With the launch of massive spectroscopic survey program such as the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) survey, the extending of available asteroseismology data from space satellites (such as Kepler), and the developments of data-driven techniques, breakthroughs have been archived in the field of Li-rich studies. In this paper, we review the progress that was made during the past four decades, and present our up-to-date understanding to Li-rich giant stars.     

Some considerations on the non-detection of interstellar Li and B towards the SN1987a

A very low upper limit of 0.15 mÅ for the interstellar 6707 Å Lii line has been recently derived towards the SN1987a by Baade and Magain (1988). This value corresponds toN(Li)<1.4×10¹¹ cm^–2 and gives [Li/H]<5.4×10^–11 assumingN(Hi)=2.6×10²¹ cm^–2 for the hydrogen column density in the LMC towards SN1987a. This value is lower than the Li abundance found in the Population II stars and lower than the minimum abundance allowed in the framework of the standard Big-Bang theory. We indirectly estimate the Li depletion usingKi observations and show that a depletion of 1.2 dex is plausible. Therefore, an interstellar abundance [Li/H] as high as 0.8×10^–9 cannot be excluded. Any improvement in the above-mentioned upper limit will place important constraints on current theories for lithium nucleosynthesis.High-resolution IUE spectra of the SN1987a have been analysed in search for IS 1362 ÅBii resonance lines. A minimum detectable equivalent width of 22 mÅ has been found, that impliesN(B)<1.2×10^–12 cm^–2 and [B/H]<4.7×10^–10 cm^–2, i.e., comparable to the solar value of [B/H]=4×10^–10. This limit is the most stringent derived so far for an external galaxy, and suggests that the rate of spallation processes in the LMC has not been higher than in our own Galaxy.     

The Chemical Evolution of the Galactic Bulge

In this paper we review the chemical evolution models for the Galactic bulge: in particular, we discuss the predictions of models as compared with the available abundance data and infer the mechanism as well as the time scale for the formation of the Galactic bulge. We show that good chemical evolution models reproducing the observed metallicity distribution of stars in the bulge predict that the [α/Fe] >0 over most of the metallicity range. This is a very important constraint indicating that the bulge of our Galaxy formed at the same time and even faster than the inner Galactic halo. We also discuss predictions for the evolution of light elements such as D and ⁷Li and conclude that the D astration should be maximum due to the high star formation rate required for the bulge whereas the evolution of the abundance of Li should be similar to that observed in the solar neighbourhood, but with an higher Li abundance in the interstellar medium at the present time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Supernova Nucleosynthesis, Chemical Evolution, and Cosmic Supernova Rate

In the chemical evolution of the Galaxy, Type II supernovae (SNe II)have contributed to the early metal enrichment and later Type Iasupernovae (SNe Ia) have contributed to the delayed enrichment of Fe.In principle, hypothetical pre-galactic population III objects couldcause the earliest heavy element enrichment. Here we present our twonew findings. 1) The peculiar abundance pattern among iron peakelements (Cr, Mn, Co, and Fe) in the very metal poor can be reproducedwith SN II nucleosynthesis yields without invoking the contributionfrom Pop III objects. 2) The observed chemical evolution in the solarneighborhood is well reproduced with the metallicity dependentoccurrence of SNe Ia, where SNe Ia do not occur if the iron abundanceof the progenitors is as low as [Fe/H] ≲ -1. We make theprediction that the cosmic SN Ia rate drops at z ∼ 1-2 because ofthe low-iron abundance, which can be observed with the Next GenerationSpace Telescope. This revised version was published online in July 2006 with corrections to the Cover Date.     

贫金属星中子俘获元素的丰度分布

在提出的贫金属星中子俘获元素丰度的计算模型基础上研究1999年新发表的21颗贫金属星的中子俘获元素丰度分布。结果表明，对较重的中子俘获元素理论预测曲线与观测值符合得很好，而对较轻的中子俘获元素二者有所偏离。这表明在贫金属环境下，对较重的中子俘获元素各核合成过程产生的丰度分布与太阳系中相应过程的丰度分布相似，但贡献比例与太阳系不同；而对较轻的中子俘获元素丰度分布与太阳系的丰度分布有所偏离；这也说明较轻的和较重的中子俘获元素的核合成场所不同，即具有不同的核合成机制。同时还特别讨论了丰度观测误差对表征各核合成过程的分量系数的影响。     

Primordial nucleosynthesis and Ω B ∼1 cosmologies with interacting radiation and matter

The constraints on the present baryon density from primordial nucleosynthesis in universes with interacting radiation and matter are investigated. For illustration, a class of exact cosmological models is studied in which two separate, interacting fluids act as the source of the gravitational field, a radiative perfect fluid modelling the cosmic microwave background and a second perfect fluid modelling the observed material content of the Universe. Althought the two fluid models under consideration are found to predict primordial element abundances similar to those predicted in the standard model (and consequently in general accord with observed values), the upper limit on the present baryon density inferred from the observed abundances of the light elements is found to be greater than that in the standard model due to the different evolution of the baryon density in the models. From this result, and using the fact that the upper limit on _B (the ratio of the present value of the baryon density to the value of the critical density) is further weakened in inhomogeneous cosmological models, it is found that unlike the situation in the standard model, cosmologies with _B 1 are permitted without violating the constraints of nucleosynthesis, thereby allowing the possibility that the Universe could be closed by baryonic matter alone.