Neutrino luminosity of stars with different masses

Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar neutrino luminosity with different masses.The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated.We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61×10^9 yr is consistent with that of the Sun.In general,neutrinos are produced by nuclear reactions,and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity.However,neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙.Although the helium flash does not produce neutrinos,plasma decay,one of the thermal processes,can efficiently make neutrinos during this stage.Due to the high mass-loss rate,a star with a mass of 9 M⊙ does not undergo the helium flash.Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage.At the end of the AGB stage,its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.

Nucleosynthesis in the accretion disks of Type Ⅱ collapsars

We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an out- ward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets trans- formed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly ad- vection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate （M） is, the higher the density and temperature are in the disks. We deal with accre- tion disks with relatively low accretion rates： 0.001 Mo s-1 ~ 3）/~ 0.01 Mo S--1 and hence these disks are predominantly advection dominated. We use He-rich and Si- rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31p, 39K, 43Sc＇ 35C1 and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthe- sized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.

Inelastic Scattering of Dark Matter with Heavy Cosmic Rays

We investigate the impact of inelastic collisions between dark matter(DM)and heavy cosmic ray(CR)nuclei on CR propagation.We approximate the fragmentation cross-sections for DM-CR collisions using collider-measured proton-nuclei scattering cross-sections,allowing us to assess how these collisions affect the spectra of CR boron and carbon.We derive new CR spectra from DM-CR collisions by incorporating their cross-sections into the source terms and solving the diffusion equation for the complete network of reactions involved in generating secondary species.In a specific example with a coupling strength of b_(χ)=0.1 and a DM mass of m_(χ)=0.1 GeV,considering a simplified scenario where DM interacts exclusively with oxygen,a notable modification in the boron-to-carbon spectrum due to the DM-CR interaction is observed.Particularly,the peak within the spectrum,spanning from 0.1 to 10 GeV,experiences an enhancement of approximately 1.5 times.However,in a more realistic scenario where DM particles interact with all CRs,this peak can be amplified to twice its original value.Utilizing the latest data from AMS-02 and DAMPE on the boron-to-carbon ratio,we estimate a 95%upper limit for the effective inelastic cross-section of DM-proton as a function of DM mass.Our findings reveal that at m_(χ)?2 MeV,the effective inelastic cross-section between DM and protons must be less than O(10^(-32))cm^(2).

Strong screening effects on resonant nuclear reaction ^(23)Mg(p,γ) ^(24)Al in the surface of magnetars

Based on the theory of relativistic superstrong magnetic fields （SMFs）, by using the method of Thomas-Fermi-Dirac approximations, we investigate the problem of strong electron screening （SES） in SMFs and the influence of SES on the nuclear reaction of 23Mg （p, Y）24A1. Our calculations show that the nuclear reaction will be markedly effected by the SES in SMFs in the surface of magnetars. Our calculated screening rates can increase two orders of magnitude due to SES in SMFs.

Direct measurement of the break-out ^(19)F(p,γ)^(20)Ne reaction in the China Jinping underground laboratory(CJPL)

Calcium production and the stellar evolution of first-generation stars remain fascinating mysteries in astrophysics.As one possible nucleosynthesis scenario,break-out from the hot carbon–nitrogen–oxygen(HCNO)cycle was thought to be the source of the calcium observed in these oldest stars.However,according to the stellar modeling,a nearly tenfold increase in the thermonuclear rate ratio of the break-out ^(19)F(p,γ)^(20) Ne reaction with respect to the competing ^(19)F(p,α)^(16) O back-processing reaction is required to reproduce the observed calcium abundance.We performed a direct measurement of this break-out reaction at the China Jinping underground laboratory.The measurement was performed down to the low-energy limit of E_(c.m.)=186 keV in the center-of-mass frame.The key resonance was observed at 225.2 keV for the first time.At a temperature of approximately 0.1 GK,this new resonance enhanced the thermonuclear ^(19)F(p,γ)^(20) Ne rate by up to a factor of≈7.4,compared with the previously recommended NACRE rate.This is of particular interest to the study of the evolution of the first stars and implies a stronger breakdown in their“warm”CNO cycle through the ^(19)F(p,γ)^(20) Ne reaction than previously envisioned.This break-out resulted in the production of the calcium observed in the oldest stars,enhancing our understanding of the evolution of the first stars.

The study of proto-magnetar winds

The velocity profiles and properties of proto-magnetar winds are investigated. It is found that the corotation of wind matter with magnetic field lines significantly affects r-process nucleosynthesis and could lead to long duration γ-ray bursts and hyper-energetic supernovae.

Quark nova model for fast radio bursts

Fast radio bursts （FRBs） are puzzling, millisecond, energetic radio transients with no discernible source; observations show no counterparts in other frequency bands. The birth of a quark star from a parent neutron star experiencing a quark nova - previously thought undetectable when born in isolation - provides a natural explanation for the emission characteristics of FRBs. The generation of unstable r-process elements in the quark nova ejecta provides millisecond exponential injection of electrons into the surrounding strong magnetic field at the parent neutron star＇s light cylinder via β-decay. This radio synchrotron emission has a total duration of hundreds of milliseconds and matches the observed spectrum while reducing the inferred dispersion measure by approximately 200 cm-3 pc. The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of β-decay chains of unstable neutron rich nuclei. Using this model, we can calculate expected FRB average energies （- 1041 erg） and spectral shapes, and provide a theoretical framework for determining distances.

The de-excited energy of electron capture in accreting neutron star crusts

When a daughter nucleus produced by electron capture takes part in a level transition from an excited state to its ground state in accreting neutron star crusts, ther- mal energy will be released and heat the crust, increasing crust temperature and chang- ing subsequent carbon ignition conditions. Previous studies show that the theoretical carbon ignition depth is deeper than the value inferred from observations because the thermal energy is not sufficient. In this paper, we present the de-excited energy from electron capture of rp-process ash before carbon ignition, especially for the initial evo- lution stage of rp-process ash, by using a level-to-level transition method. We find the theoretical column density of carbon ignition in the resulting superbursts and compare it with observations. The calculation of the electron capture process is based on a more reliable level-to-level transition, adopting new data from experiments or theo- retical models （e.g., large-scale shell model and proton-neutron quasi-particle random phase approximation）. The new carbon ignition depth is estimated by fitting from previous results of a nuclear reaction network. Our results show the average de-excited energy from electron capture before carbon ignition is -0.026 MeV/u, which is significantly larger than the previous results. This energy is beneficial for enhancing the crust＇s temperature and decreasing the carbon ignition depth of superbursts.

Sodium Enrichment in Yellow Supergiants:a Perspective from the Uncertainties of Reaction Rates

Sodium overabundance in yellow supergiants has stumped people for more than 20 years. The purpose of this paper is to explore this problem from the perspective of nuclear physics. We investigate carefully the CNO and NeNa cycles that are responsible for sodium production. We investigate some key reactions in the appropriate network. We show whether and how the sodium output can be affected by the rate uncertainties in these reactions. In this way, we evaluate if a reaction is important enough to deserve a better determination of its rate in terrestrial laboratories.

Beta decay of nuclides ^(56)Fe,^(62)Ni,^(64)Ni and ^(68)Ni in the crust of magnetars

By introducing the Dirac δ-function and Pauli exclusion principle in the presence of superstrong magnetic fields （SMFs）, we investigate the influence of SMFs on beta decay and the change rates of electron fraction （CREF） of nuclides 56Fe, 62Ni, 64Ni and 6SNi in magnetars, which are powered by magnetic field energy. We find that the magnetic fields have a great influence on the beta decay rates, and the beta decay rates can decrease by more than six orders of magnitude in the presence of SMFs. The CREF also decreases by more than seven orders of magnitude in the presence of SMFs.

Dynamics of neutrino-driven winds:inclusion of accurate weak interaction rates in strong magnetic fields

Solving Newtonian steady-state wind equations while considering the ac- curate weak interaction rates and magnetic fields （MFs） of young neutron stars, we study the dynamics and nucleosynthesis of neutrino-driven winds （NDWs） from proto neutron stars （PNSs）. For a typical 1.4 Mo PNS model, we find that the nucleosyn- thesis products are closely related to the luminosity of neutrinos and anti-neutrinos. The lower the luminosity is, the larger is the effect on the NDWs caused by weak in- teractions and MFs. At a high anti-neutrino luminosity of typically 8 × 1051 erg s-1, neutrinos and anti-neutrinos dominate the processes in an NDW and the MFs hardly change the wind＇s properties. But at a low anti-neutrino luminosity of 1051 erg s-1 at the late stage of an NDW the mass of the product and process of nucleosynthesis are changed significantly in strong MFs. Therefore, in most of the models considered for the NDWs from PNSs, based on our calculations, the influences of MFs and the net weak interactions on the nucleosynthesis are not significant.

Supernova β^- decay of nuclides ^(53)Fe,^(54)Fe,^(55)Fe and ^(56)Fe in strongly screened plasma

Electron screening has strong effects on electron energy and threshold energy of the beta decay reaction.In this paper,we study β~-decay rates of some iron isotopes.The beta decay rates increase by about two orders of magnitude due to electron screening.Strongly screened beta decay rates due to Q-value correction are more than one order of magnitude higher than those without Q-value correction.

Iron group nuclei electron capture in super-Chandrasekhar superstrong magnetic white dwarfs

Using the theory of relativistic mean-field effective interactions,the influences of superstrong magnetic fields(SMFs)on electron Fermi energy,binding energy per nucleus and single-particle level structure are discussed in super-Chandrasekhar magnetic white dwarfs.Based on the relativistical SMFs theory model of Potekhin et al.,the electron chemical potential is corrected in SMFs,and the electron capture(EC)of iron group nuclei is investigated by using the Shell-Model Monte Carlo method and Random Phase Approximation theory.The EC rates can increase by more than three orders of magnitude due to the increase of the electron Fermi energy and the change of single-particle level structure by SMFs.However,the EC rates can decrease by more than four orders of magnitude due to increase of the nuclei binding energy by SMFs.We compare our results with those of FFNs(Fuller et al.),AUFDs(Aufderheide et al.)and Nabi(Nabi et al.).Our rates are higher by about four orders of magnitude than those of FFN,AUFD and Nabi due to SMFs.Our study may have important reference value for subsequent studies of the instability,mass radius relationship,and thermal and magnetic evolution of super-Chandrasekhar magnetic white dwarfs.

贫金属星重元素丰度分布的参数化研究

基于大量贫金属星元素丰度的观测资料,以太阳系重元素丰度分布为标准,选取Sr、Ba、Eu分别作为贫金属星弱s-过程、主要s-过程、r-过程3种核合成的典型元素,采用参数化方法,分析了不同核合成过程对贫金属星重元素丰度的贡献比例.研究表明:金属丰度越高,弱s-过程、主要s-过程对较轻的中子俘获元素丰度的贡献就越大,较重的中子俘获元素主要由r-过程和主要s-过程产生;金属丰度较低,重中子俘获元素丰度主要由r-过程产生,星系早期弱s-过程对元素丰度几乎没有贡献.

AGB星核合成理论的研究进展

综述了近年来AGB星核合成的理论研究情况,包括轻、重核素核合成理论、AGB星的分类、AGB星的演化特征、AGB星内的元素核合成理论的研究及外赋MS、S星的双星吸积机制的研究情况。

大爆炸核合成研究的新进展

阐明了标准大爆炸核合成（SBBN）模型的理论和观测状况，着重讨论了1994年的最新进展：已有3位有效数字的4He丰度原初值Y4P与由银河系观测推得的D＋3He丰度原初值Y23p间出现矛盾的可能性，使SBBN模型面临考验；高红移吸收云中氘丰度测量的有关结果与原有Y23p显著矛盾，而与Y4p偏小的趋向相洽，可能对银河系化学演化模型提出质疑。因此，河外HⅡ区中氦丰度和高红移吸收云中氘气丰度的进一步测量以及D和3He丰度化学演化的研究值得重视。

恒星尘埃的实验室研究——实验天体物理学

原始球粒陨石含有来自恒星的微小固体颗粒(微米级),这些尘埃的同位素组成与太阳系物质截然不同,它们是目前唯一能直接获得的恒星固体样品．已发现的恒星尘埃有金刚石、石墨、碳化硅、刚玉、尖晶石、氮化物、和硅酸盐等,它们的母体恒星包括红巨星,AGB恒星、新星和超新星．对恒星尘埃的研究,使得更深入地了解星系的化学演化历史、恒星内部的核反应和湍流机制、恒星大气中尘埃的形成、星际介质物理现象等．恒星尘埃把天体物理领域延伸到了微观世界,它有机地结合了地球化学实验技术和天体物理理论,开辟了一门崭新的天文学分支实验天体物理学．

Resonant nuclear reaction 23Mg(p,γ) 24Al in strongly screening magnetized neutron star crust

Based on the relativistic theory of superstrong magnetic fields（SMF）, by using three models those of Lai（LD）, Fushiki（FGP）, and our own（LJ）, we investigate the influence of SMFs due to strong electron screening（SES） on the nuclear reaction 23Mg（p,γ） 24Al in magnetars. In a relatively low density environment（e.g., ρ7 〈0.01）and 1 〈 B12 〈 102, our screening rates are in good agreement with those of LD and FGP. However, in relatively high magnetic fields（e.g., B12 〉102）, our reaction rates can be 1.58 times and about three orders of magnitude larger than those of FGP and LD, respectively（B12, ρ7 are in units of 1012G, 107 g cm-3）. The significant increase of strong screening rate can imply that more 23Mg will escape from the Ne-Na cycle due to SES in a SMF. As a consequence,the next reaction, 24Al（＋β, ν） 24Mg, will produce more 24Mg to participate in the Mg-Al cycle. Thus, it may lead to synthesis of a large amount of A〉20 nuclides in magnetars.

Collapse Velocity and Prompt Explosion for the Presupernova Model Ws15M_⊙

For the presupernova modelWs15M⊙, we re-calculate the electron capture （EC） timescale and hydrodynamical （HD） timescale. We found that the EC timescale can be smaller than the HD timescale in the inner region of the collapse iron core at the moment immediately before the shock wave bounce. The change in these two timescales at the late stage of core collapse is expected to affect the collapse velocity. If the late-time collapse velocity is artificially increased by a small quantity, then prompt explosion of the supernova may happen. Further calculations are still needed to check the plausibility of the acceleration mechanism caused by the faster EC process.

恒星在AGB阶段的结构演化及其特征

综述了近年来关于 ＡＧＢ星演化的研究进展情况、ＡＧＢ星的演化特征。