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New insights into the limit of the magnetic monopole flux and the heatingsource in white dwarfs

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中国物理C:英文版 2023年第8期47卷 95-106页

作者：刘晶晶刘冬梅郝良焕 College of Science Hainan Tropical Ocean UniversitySanya 572022China

Based on the magnetic monopole(MM)catalytic nuclear decay(Rubakov-Callan(RC)effect),we propose five new models to discuss the limit of the MM flux and the heating energy resources of white dwarfs(WDs)based on observations of 13 red giant branch(RGB)stars.We find that the number of MMs captured can reach a maximum value of 9.1223×10^(24)when m=10^(17)GeV,nB=5.99×10^(31)cm^(-3),Φ=7.59×10^(-26)cm^(-2)s^(-1)sr^(-1).The good agreement of our calculated luminosities for WDs with observation provides support for our model based on the RC effect by MMs.We obtain a new limit of the MM flux of ξ=Φ(σ_(m)^(v)T)_(-28)≤9.0935×10^(-13)cm^(-2)s^(-1)sr^(-1),and≤4.9950×10^(-13)cm^(-2)s^(-1)sr^(-1)at nB=5.99×1031cm-3 when m=1015GeV,β=9.4868×10^(-3),and m=1017Gev,β=10^(-3),respectively.Our results show that the RC effect could cause heating that prevents white dwarfs from cooling down into a stellar graveyard.Our results will also provide a new idea for further research on the upper limit of MM flow(note:nB,σ_(m),m,φ,ξ,are the baryon number density,reaction cross section,mass,MM flux,and the new limit of the MM flux,respectively,andβ=v_(T/C)is the ratio of the speed of MMs to that of light).

关键词： white dwarfs evolution nuclear reactions

The C/O ratio of He-accreting carbon-oxygen white dwarfs and type Ia supernovae

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Research in Astronomy and Astrophysics 2020年第1期20卷 19-26页

作者：崔晓王博吴程远孟祥存韩占文 Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China University of the Chinese Academy of Sciences Beijing 100049China

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.

关键词： stars:evolution supernovae:general white dwarfs

Why Don’t Cold white dwarfs Exist?

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Journal of High Energy Physics, Gravitation and Cosmology 2023年第2期9卷 438-444页

作者： Qiuhe Peng Jingjing Liu Department of Astronomy Nanjing University Nanjing China College of Science Hainan Tropical Ocean University Sanya China

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... 详细信息

关键词： white dwarfs The Energy Source Magnetic Monopoles

Stellar structure model in hydrostatic equilibrium in the context of f(R)-gravity

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Research in Astronomy and Astrophysics 2017年第12期17卷 31-40页

作者： Raíla Andr Gilberto M.Kremer Departamento de Fisica Universidade Federal do Parana81531-980 CuritibaBrazil Manipal Centre for Natural Sciences Manipal UniversityManipal 576104India

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.

关键词： cosmology：theory stars：general massive brown dwarfs white dwarfs neutron

The formation of neutron star systems through accretion-induced collapse in white-dwarf binaries

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Research in Astronomy and Astrophysics 2020年第9期20卷 135-158页

作者： Bo Wang Dongdong Liu Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China

The accretion-induced collapse(AIC)scenario was proposed 40 years ago as an evolutionary end state of oxygen-neon white dwarfs(ONe WDs),linking them to the formation of neutron star(NS)systems.However,there has been no direct detection of any AIC event so far,even though there exists a lot of indirect observational evidence.Meanwhile,the evolutionary pathways resulting in NS formation through AIC are still not thoroughly investigated.In this article,we review recent studies on the two classic progenitor models of AIC events,i.e.,the single-degenerate model(including the ONe WD+MS/RG/He star channels and the CO WD+He star channel)and the double-degenerate model(including the double CO WD channel,the double ONe WD channel and the ONe WD+CO WD channel).Recent progress on these progenitor models is reviewed,including the evolutionary scenarios leading to AIC events,the initial parameter space for producing AIC events and the related objects(e.g.,the pre-AIC systems and the post-AIC systems).For the single-degenerate model,the pre-AIC systems(i.e.,the progenitor systems of AIC events)could potentially be identified as supersoft X-ray sources,symbiotics and cataclysmic variables(such as classical novae,recurrent novae,Ne novae and He novae)in the observations,whereas the post-AIC systems(i.e.,NS systems)could potentially be identified as low-/intermediate-mass X-ray binaries,and the resulting low-/intermediate-mass binary pulsars,most notably millisecond pulsars.For the double-degenerate model,the pre-AIC systems are close double WDs with short orbital periods,whereas the post-AIC systems are single isolated NSs that may correspond to a specific kind of NS with peculiar properties.We also review the predicted rates of AIC events,the mass distribution of NSs produced via AIC and the gravitational wave(GW)signals from double WDs that are potential GW sources in the Galaxy in the context of future spacebased GW detectors,such as LISA,TianQin,Taiji,etc.Recent theoretical and observational constraints on the detection of AI

关键词： binaries:close white dwarfs supernovae:general stars:neutron stars:evolution

Quantum Instability of Magnetized Stellar Objects

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Chinese Journal of Astronomy and Astrophysics 2005年第4期5卷 399-411页

作者： R. González Felipe H. J. Mosquera Cuesta A. Pérez Martínez H. Pérez Rojas Departamento de Física and Centro de Física Teórica de Partículas Instituto Superior Técnico Av. Rovisco Pais 1049-001 Lisboa PortugalInstituto de Cosmologia Relatividade e Astrofísica (ICRA-BR) Centre Brasileiro de Pesquisas Físicas Rua Dr. Xavier Sigaud 150 CEP 22290-180 Urea Rio de Janeiro RJBrazilCentro Latino-Americano de Física Avenida Wenceslau Braz 71 CEP 22290-140 fundosBotafogo Rio de Janeiro BrazilInstituto de Cibernética Matemática y Física Calle E No. 309 10400 La Habana CubaInstituto de Cibernética Matemática y Física Calle E No. 309 10400 La Habana Cuba

The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.

关键词： dense matter-equation of state-instabilities-stars： magnetic fields-stars： neutron white dwarfs

The gravitational wave emission of double white dwarf coalescences

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Research in Astronomy and Astrophysics 2020年第9期20卷 164-170页

作者：邹泽城周小龙黄永锋 School of Astronomy and Space Science Nanjing UniversityNanjing 210023China Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University) Ministry of EducationNanjing 210023China

Type Ia Supernovae(SNe Ia)are widely used as standard candles to probe the Universe.However,how these fierce explosions are produced itself is still a highly debated issue.There are mainly two popular models for SNe Ia:the double-degenerate scenario and the single-degenerate scenario.The doubledegenerate scenario suggests that SNe Ia are produced by the coalescence of two degenerate white dwarfs,while the single-degenerate scenario suggests that the continuous accretion of a single degenerate white dwarf from its normal stellar companion will finally lead to a disastrous explosion when it is over-massive,resulting in an SN Ia.The rapid development of the gravitational wave astronomy sheds new light on the nature of SNe Ia.In this study,we calculate the gravitational wave emissions of double white dwarf coalescences and compare them with the sensitivities of several upcoming detectors.It is found that the gravitational wave emissions from double white dwarf mergers in the local universe are strong enough to be detected by LISA.We argue that LISA-like gravitational wave detectors sensitive in the frequency range of 0.01—0.1 Hz will be a powerful tool to test the double-degenerate model of SNe Ia,and also to probe the Universe.

关键词： white dwarfs gravitational waves supernovae:general

A triplet of the only pulsation mode detected in the DAV star G132–12

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Research in Astronomy and Astrophysics 2021年第6期21卷 276-280页

作者： Wen-Chao Su Jian-Ning Fu Jian-Xing Chen Lester Fox-Machado Shi-Jie Zhao Carmen Ayala-Loera Jiang-Tao Wang Yang Pan Department of Astronomy Beijing Normal UniversityBeijing 100012China Dipartimento di Fisica e Astronomia Alma Mater Studiorum Universita’di Bolognavia Piero Gobetti 93/21-40129 BolognaItaly INAF-Osservatorio di Astrofisica e Scienze dello Spazio di Bologna Via Piero Gobetti 93/31-40129 BolognaItaly Instituto de Astronomia Universidad Nacional Autonoma de MexicoApartado Postal 87722800 EnsenadaBaja CaliforniaMexico Institute of Astronomy&Astrophysics Academia SinicaTaipeiChina

Hydrogen atmosphere pulsating white dwarfs,also known as DAV stars,are the most abundant type of pulsating white dwarfs.High-temperature DAV stars in general exhibit a small number of pulsation modes and stable frequencies.G132-12 is one of the pulsating hydrogen atmosphere white dwarf stars which lies close to the blue edge of the instability strip.Previous researches reported that G132-12 might have only one pulsation mode with the period of 212.69 s.To study the pulsation properties of G132-12 in detail,we carried out a bi-site observation campaign in October 2019.Time series photometric data were collected during around 154 h in total.A Fourier analysis reveals three frequencies which are identified as the triplet of an l=1 g-mode pulsation with the period of 212.499 s.The rotational period is derived as Prot=35.0±6.7 h and the inclination of the rotational axis to the line of sight is 70°.G132-12 could be an ideal target for measuring the cooling scale of this white dwarf star with only one excited pulsation mode detected.

关键词： white dwarfs oscillations photometric