In this work we apply the differential transformation method or DTM for solving some classes of Lane-Emden type equations as a model for the dimensionless density distribution in an isothermal gas sphere and as a stud...In this work we apply the differential transformation method or DTM for solving some classes of Lane-Emden type equations as a model for the dimensionless density distribution in an isothermal gas sphere and as a study of the gravitational potential of (white-dwarf) stars , which are nonlinear ordinary differential equations on the semi-infinite domain [1] [2]. The efficiency of the DTM is illustrated by investigating the convergence results for this type of the Lane-Emden equations. The numerical results show the reliability and accuracy of this method.展开更多
In this work we apply the differential transformation method (Zhou’s method) or DTM for solving white-dwarfs equation which Chandrasekhar [1] introduced in his study of the gravitational potential of these degenerate...In this work we apply the differential transformation method (Zhou’s method) or DTM for solving white-dwarfs equation which Chandrasekhar [1] introduced in his study of the gravitational potential of these degenerate (white-dwarf) stars. DTM may be considered as alternative and efficient for finding the approximate solutions of the initial values problems. We prove superiority of this method by applying them on the some Lane-Emden type equation, in this case. The power series solution of the reduced equation transforms into an approximate implicit solution of the original equation.展开更多
Why no late type M and much later type N white dwarfs with surface temperatures less than 3000 K had ever been observed? What are the heat sources of these later type white dwarfs? In this paper, we find that the ener...Why no late type M and much later type N white dwarfs with surface temperatures less than 3000 K had ever been observed? What are the heat sources of these later type white dwarfs? In this paper, we find that the energy source of white dwarfs is the nucleons decay catalyzed by magnetic monopoles.展开更多
In this work we present a stellar structure model from the f（R）-gravity point of view capable of describing some classes of stars（white dwarfs, brown dwarfs, neutron stars, red giants and the Sun）. This model is b...In this work we present a stellar structure model from the f（R）-gravity point of view capable of describing some classes of stars（white dwarfs, brown dwarfs, neutron stars, red giants and the Sun）. This model is based on f（R）-gravity field equations for f（R） = R ＋ f2R2, hydrostatic equilibrium equation and a polytropic equation of state. We compare the results obtained with those found by Newtonian theory. It has been observed that in these systems, where high curvature regimes emerge,stellar structure equations undergo modifications. Despite the simplicity of this model, the results are satisfactory. The estimated values of pressure, density and temperature of the stars are within those determined by observations. This f（R）-gravity model has proved to be necessary to describe stars with strong fields such as white dwarfs, neutron stars and brown dwarfs, while stars with weaker fields, such as red giants and the Sun, are best described by Newtonian theory.展开更多
中国空间站工程巡天望远镜(China Space Station Telescope,CSST)计划于2024年发射,将主要开展高空间分辨率、天区大面积(约17500平方度)的多色成像与无缝光谱巡天,预计可极大地提高白矮星的观测样本数量.本文分别基于盖亚第三次早期数...中国空间站工程巡天望远镜(China Space Station Telescope,CSST)计划于2024年发射,将主要开展高空间分辨率、天区大面积(约17500平方度)的多色成像与无缝光谱巡天,预计可极大地提高白矮星的观测样本数量.本文分别基于盖亚第三次早期数据发布(Gaia EDR3)和斯隆数字巡天第十六次数据发布(SDSS DR16)探测到的白矮星候选体和已确认的白矮星样本,进行统计分析,得出恒星参数的分布(多波段星等、有效温度、表面重力加速度、距离和质量),并分析各参数之间的相关性,计算白矮星的空间密度;最后,结合CSST的观测性能,预计其将探测到的白矮星数目,为基于CSST主巡天数据开展大样本暗弱白矮星搜寻和研究工作提供预估和分析.展开更多
Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclea...Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model accounts for only about 1/2-2/3 of the observations. If a single starburst is assumed, the distribution of the delay times of SNe Ia from the SD model is a weak bimodality, where the WD + He channel contributes to the SNe Ia with delay times shorter than 100 Myr, and the WD + MS and WD + RG channels to those with age longer than 1 Gyr.展开更多
Although type Ia supernovae(SNe Ia) show their importance in many astrophysical fields,the nature of the progenitors of SNe Ia is still unclear.At present,the single degenerate(SD) model is presented to be a very like...Although type Ia supernovae(SNe Ia) show their importance in many astrophysical fields,the nature of the progenitors of SNe Ia is still unclear.At present,the single degenerate(SD) model is presented to be a very likely progenitor model.Following the comprehensive SD model developed by Meng & Yang(2010),we show the initial and final state of the progenitor systems of SNe Ia in an orbital period—the secondary mass(log Pi,M2i) plane.Our results may explain the location of some supersoft X-ray sources and recurrent novae in the(log Pi,M2i) plane,and be helpful to judge whether an SD system is the potential progenitor system of SNe Ia,as well as to simulate the interaction between SN ejecta and its companion.展开更多
The Galactic hard X-ray transient SWIFT J195509+261406 was first observed as gamma-ray burst GRB 070610.Within 3 days after the burst,more than forty optical flares had been observed.Here,we propose that this peculiar...The Galactic hard X-ray transient SWIFT J195509+261406 was first observed as gamma-ray burst GRB 070610.Within 3 days after the burst,more than forty optical flares had been observed.Here,we propose that this peculiar event should be associated with a white dwarf.The hard X-ray burst itself may be triggered by a collision between two planets orbiting the white dwarf.Some cracked fragments produced in the collision then fell onto the surface of the white dwarf over several days,giving birth to the observed optical flares via cyclotron radiation.Our model can satisfactorily explain the basic features of the observations.展开更多
I construct the class of supernovae and supernova progenitors that result from fatal common envelope evolution(CEE). The fatal CEE progenitors are stellar binary systems where a companion spirals-in inside the envelop...I construct the class of supernovae and supernova progenitors that result from fatal common envelope evolution(CEE). The fatal CEE progenitors are stellar binary systems where a companion spirals-in inside the envelope of a giant star and merges with the core. The companion can be a neutron star(NS;or a black hole) that destroys the core and by that forms a common envelope jets supernova(CEJSN), a white dwarf(WD) that merges with the core to form a massive WD that later might explode as a Type Ia supernova(the core degenerate scenario), or a main sequence companion. In the latter case the outcome might be a core collapse supernova(CCSN) of a blue giant, a CCSN of type IIb or of type Ib. In another member of this class two giant stars merge and the two cores spiral-in toward each other to form a massive core that later explodes as a CCSN with a massive circumstellar matter(CSM). I discuss the members of this class, their characteristics, and their common properties. I find that fatal CEE events account for ≈6%-10% of all CCSNe, and raise the possibility that a large fraction of peculiar and rare supernovae result from the fatal CEE. The study of these supernova progenitors as a class will bring insights on other types of supernova progenitors, as well as on the outcome of the CEE.展开更多
It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a doub...It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a double carbon-oxygen white dwarf(CO WD) merges. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2–428 consists of a double CO WD system that has a total mass of^1.76 M⊙, a mass ratio of^1 and an orbital period of^4.2 h, which is the first and only discovered progenitor candidate for an SN Ia predicted by the violent merger scenario. In this work, we aim to reproduce the evolutionary history of the central double CO WD of Henize 2–428. We find that the planetary nebula Henize 2–428 may originate from a primordial binary that has a^5.4 M⊙primary and a^2.7 M⊙secondary with an initial orbital period of^15.9 d. The double CO WD was formed after the primordial binary experienced two Roche-lobe overflows and two common-envelope ejection processes.According to our calculations, it takes about^840 Myr for the double CO WD to merge and form an SN Ia driven by gravitational wave radiation after their birth. To produce the current status of Henize 2–428,a large common-envelope parameter is needed. We also estimate that the rate of SNe Ia from the violent merger scenario is at most 2.9 × 10^(-4) yr^(-1), and that the delay time is in the range of^90 Myr to the Hubble time.展开更多
Type Ia supernovae(SNe Ia)are thermonuclear explosions of carbon-oxygen white dwarfs(CO WDs),and are believed to be excellent cosmological distance indicators due to their high luminosity and remarkable uniformity.How...Type Ia supernovae(SNe Ia)are thermonuclear explosions of carbon-oxygen white dwarfs(CO WDs),and are believed to be excellent cosmological distance indicators due to their high luminosity and remarkable uniformity.However,there exists a diversity among SNe Ia,and a poor understanding of the diversity hampers the improvement of the accuracy of cosmological distance measurements.The variations of the ratios of carbon to oxygen(C/O)of WDs at explosion are suggested to contribute to the diversity.In the canonical model of SNe Ia,a CO WD accretes matter from its companion and increases its mass till the Chandrasekhar mass limit when the WD explodes.In this work,we studied the C/O ratio for accreting CO WDs.Employing the stellar evolution code MESA,we simulated the accretion of He-rich material onto CO WDs with different initial WD masses and different mass accretion rates.We found that the C/O ratio varies for different cases.The C/O ratio of He-accreting CO WDs at explosion increases with a decreasing initial WD mass or a decreasing accretion rate.The various C/O ratios may,therefore,contribute to the diversity of SNe Ia.展开更多
We have found that fractional principal quantum numbers are permitted in hydrogen atom which yield the conditions for neutron and white dwarf stars evolution. The number densities of neutron and white dwarf stars reve...We have found that fractional principal quantum numbers are permitted in hydrogen atom which yield the conditions for neutron and white dwarf stars evolution. The number densities of neutron and white dwarf stars reveal that these systems have the maximal conductivity of 1.37×1010Ω-1m-1. They are giant perfect conductors at very high temperature and magnetic field.展开更多
文摘In this work we apply the differential transformation method or DTM for solving some classes of Lane-Emden type equations as a model for the dimensionless density distribution in an isothermal gas sphere and as a study of the gravitational potential of (white-dwarf) stars , which are nonlinear ordinary differential equations on the semi-infinite domain [1] [2]. The efficiency of the DTM is illustrated by investigating the convergence results for this type of the Lane-Emden equations. The numerical results show the reliability and accuracy of this method.
文摘In this work we apply the differential transformation method (Zhou’s method) or DTM for solving white-dwarfs equation which Chandrasekhar [1] introduced in his study of the gravitational potential of these degenerate (white-dwarf) stars. DTM may be considered as alternative and efficient for finding the approximate solutions of the initial values problems. We prove superiority of this method by applying them on the some Lane-Emden type equation, in this case. The power series solution of the reduced equation transforms into an approximate implicit solution of the original equation.
文摘Why no late type M and much later type N white dwarfs with surface temperatures less than 3000 K had ever been observed? What are the heat sources of these later type white dwarfs? In this paper, we find that the energy source of white dwarfs is the nucleons decay catalyzed by magnetic monopoles.
文摘In this work we present a stellar structure model from the f（R）-gravity point of view capable of describing some classes of stars（white dwarfs, brown dwarfs, neutron stars, red giants and the Sun）. This model is based on f（R）-gravity field equations for f（R） = R ＋ f2R2, hydrostatic equilibrium equation and a polytropic equation of state. We compare the results obtained with those found by Newtonian theory. It has been observed that in these systems, where high curvature regimes emerge,stellar structure equations undergo modifications. Despite the simplicity of this model, the results are satisfactory. The estimated values of pressure, density and temperature of the stars are within those determined by observations. This f（R）-gravity model has proved to be necessary to describe stars with strong fields such as white dwarfs, neutron stars and brown dwarfs, while stars with weaker fields, such as red giants and the Sun, are best described by Newtonian theory.
文摘中国空间站工程巡天望远镜(China Space Station Telescope,CSST)计划于2024年发射,将主要开展高空间分辨率、天区大面积(约17500平方度)的多色成像与无缝光谱巡天,预计可极大地提高白矮星的观测样本数量.本文分别基于盖亚第三次早期数据发布(Gaia EDR3)和斯隆数字巡天第十六次数据发布(SDSS DR16)探测到的白矮星候选体和已确认的白矮星样本,进行统计分析,得出恒星参数的分布(多波段星等、有效温度、表面重力加速度、距离和质量),并分析各参数之间的相关性,计算白矮星的空间密度;最后,结合CSST的观测性能,预计其将探测到的白矮星数目,为基于CSST主巡天数据开展大样本暗弱白矮星搜寻和研究工作提供预估和分析.
基金supported by the National Natural Science Foundation of China (Grant No. 10821061)the National Basic Research Program of China (Grant No. 2007CB815406)the Yunnan Natural Science Foundation (Grant No. 08YJ041001)
文摘Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model accounts for only about 1/2-2/3 of the observations. If a single starburst is assumed, the distribution of the delay times of SNe Ia from the SD model is a weak bimodality, where the WD + He channel contributes to the SNe Ia with delay times shorter than 100 Myr, and the WD + MS and WD + RG channels to those with age longer than 1 Gyr.
基金supported by the National Natural Science Foundation of China (Grant No 10963001)the Project of the Fundamental and Frontier Research of Henan Province (Grant No 102300410223)
文摘Although type Ia supernovae(SNe Ia) show their importance in many astrophysical fields,the nature of the progenitors of SNe Ia is still unclear.At present,the single degenerate(SD) model is presented to be a very likely progenitor model.Following the comprehensive SD model developed by Meng & Yang(2010),we show the initial and final state of the progenitor systems of SNe Ia in an orbital period—the secondary mass(log Pi,M2i) plane.Our results may explain the location of some supersoft X-ray sources and recurrent novae in the(log Pi,M2i) plane,and be helpful to judge whether an SD system is the potential progenitor system of SNe Ia,as well as to simulate the interaction between SN ejecta and its companion.
基金supported by the National Natural Science Foundation of China (Grant No. 10625313)the National Basic Research Program of China (Grant No. 2009CB824800)
文摘The Galactic hard X-ray transient SWIFT J195509+261406 was first observed as gamma-ray burst GRB 070610.Within 3 days after the burst,more than forty optical flares had been observed.Here,we propose that this peculiar event should be associated with a white dwarf.The hard X-ray burst itself may be triggered by a collision between two planets orbiting the white dwarf.Some cracked fragments produced in the collision then fell onto the surface of the white dwarf over several days,giving birth to the observed optical flares via cyclotron radiation.Our model can satisfactorily explain the basic features of the observations.
基金supported by the E. and J. Bishop Research Fund at the Technionby a grant from the Israel Science Foundation
文摘I construct the class of supernovae and supernova progenitors that result from fatal common envelope evolution(CEE). The fatal CEE progenitors are stellar binary systems where a companion spirals-in inside the envelope of a giant star and merges with the core. The companion can be a neutron star(NS;or a black hole) that destroys the core and by that forms a common envelope jets supernova(CEJSN), a white dwarf(WD) that merges with the core to form a massive WD that later might explode as a Type Ia supernova(the core degenerate scenario), or a main sequence companion. In the latter case the outcome might be a core collapse supernova(CCSN) of a blue giant, a CCSN of type IIb or of type Ib. In another member of this class two giant stars merge and the two cores spiral-in toward each other to form a massive core that later explodes as a CCSN with a massive circumstellar matter(CSM). I discuss the members of this class, their characteristics, and their common properties. I find that fatal CEE events account for ≈6%-10% of all CCSNe, and raise the possibility that a large fraction of peculiar and rare supernovae result from the fatal CEE. The study of these supernova progenitors as a class will bring insights on other types of supernova progenitors, as well as on the outcome of the CEE.
基金supported by the National Natural Science Foundation of China (Nos. 11873085, 11673059 and 11521303)Chinese Academy of Sciences (Nos. QYZDB-SSW-SYS001 and KJZD-EW-M06-01)Yunnan Province (Nos. 2017HC018 and 2018FB005)
文摘It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a double carbon-oxygen white dwarf(CO WD) merges. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2–428 consists of a double CO WD system that has a total mass of^1.76 M⊙, a mass ratio of^1 and an orbital period of^4.2 h, which is the first and only discovered progenitor candidate for an SN Ia predicted by the violent merger scenario. In this work, we aim to reproduce the evolutionary history of the central double CO WD of Henize 2–428. We find that the planetary nebula Henize 2–428 may originate from a primordial binary that has a^5.4 M⊙primary and a^2.7 M⊙secondary with an initial orbital period of^15.9 d. The double CO WD was formed after the primordial binary experienced two Roche-lobe overflows and two common-envelope ejection processes.According to our calculations, it takes about^840 Myr for the double CO WD to merge and form an SN Ia driven by gravitational wave radiation after their birth. To produce the current status of Henize 2–428,a large common-envelope parameter is needed. We also estimate that the rate of SNe Ia from the violent merger scenario is at most 2.9 × 10^(-4) yr^(-1), and that the delay time is in the range of^90 Myr to the Hubble time.
基金supported by the National Natural Science Foundation of China(Grant Nos.11521303,11873085,11673059 and 11733008)the Chinese Academy of Sciences(QYZDB-SSW-SYS001)the Natural Science Foundation of Yunnan Province(2015HB096 and 2018FB005)
文摘Type Ia supernovae(SNe Ia)are thermonuclear explosions of carbon-oxygen white dwarfs(CO WDs),and are believed to be excellent cosmological distance indicators due to their high luminosity and remarkable uniformity.However,there exists a diversity among SNe Ia,and a poor understanding of the diversity hampers the improvement of the accuracy of cosmological distance measurements.The variations of the ratios of carbon to oxygen(C/O)of WDs at explosion are suggested to contribute to the diversity.In the canonical model of SNe Ia,a CO WD accretes matter from its companion and increases its mass till the Chandrasekhar mass limit when the WD explodes.In this work,we studied the C/O ratio for accreting CO WDs.Employing the stellar evolution code MESA,we simulated the accretion of He-rich material onto CO WDs with different initial WD masses and different mass accretion rates.We found that the C/O ratio varies for different cases.The C/O ratio of He-accreting CO WDs at explosion increases with a decreasing initial WD mass or a decreasing accretion rate.The various C/O ratios may,therefore,contribute to the diversity of SNe Ia.
文摘We have found that fractional principal quantum numbers are permitted in hydrogen atom which yield the conditions for neutron and white dwarf stars evolution. The number densities of neutron and white dwarf stars reveal that these systems have the maximal conductivity of 1.37×1010Ω-1m-1. They are giant perfect conductors at very high temperature and magnetic field.
