TypeⅠa supernovae(SNe Ia)are among the most energetic events in the universe.They are excellent cosmological distance indicators due to the remarkable homogeneity of their light curves.However,the nature of the proge...TypeⅠa supernovae(SNe Ia)are among the most energetic events in the universe.They are excellent cosmological distance indicators due to the remarkable homogeneity of their light curves.However,the nature of the progenitors of SNeⅠa is still not well understood.In the single-degenerate model,a carbon-oxygen white dwarf(CO WD)could grow its mass by accreting material from an asymptotic giant branch(AGB)star,leading to the formation of SNe Ia when the mass of the WD approaches to the Chandrasekhar-mass limit,known as the AGB donor channel.In this channel,previous studies mainly concentrate on the wind-accretion pathway for the mass-increase of the WDs.In the present work,we employed an integrated mass-transfer prescription for the semidetached WD+AGB systems,and evolved a number of WD+AGB systems for the formation of SNe Ia through the Roche-lobe overflow process or the wind-accretion process.We provided the initial and final parameter spaces of WD+AGB systems for producing SNe Ia.We also obtained the density distribution of circumstellar matter at the moment when the WD mass reaches the Chandrasekhar-mass limit.Moreover,we found that the massive WD+AGB sample AT 2019qyl can be covered by the final parameter space for producing SNe Ia,indicating that AT 2019qyl is a strong progenitor candidate of SNe Ia with AGB donors.展开更多
The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way.However,the search for double white dwarfs in the gravitational wave data will be time-consu...The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way.However,the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation.In this paper,we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data.To quickly determine the rough parameters of the target sources,the following algorithms are adopted in a coarse search process:(1)using the downsampling method to reduce the number of original data points;(2)using the undersampling method to speed up the generation of a single waveform template;(3)using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space;(4)combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template.A fine search process is applied to further determine the parameters of the signals based on the coarse search,for which we adopt the particle swarm optimization.Finally,we detect O(10^(4))double white dwarf signals,validating the feasibility of our method.展开更多
The white dwarf(WD)+helium(He)star binary channel plays an important role in the single degenerate scenario for the progenitors of type Ia supernovae(SNe Ia).Previous studies on the WD+main sequence star evolution hav...The white dwarf(WD)+helium(He)star binary channel plays an important role in the single degenerate scenario for the progenitors of type Ia supernovae(SNe Ia).Previous studies on the WD+main sequence star evolution have shown that the magnetic fields of WDs may significantly influence their accretion and nuclear burning processes.In this work we focus on the evolution of magnetized WD+He star binaries with detailed stellar evolution and binary population synthesis(BPS)calculations.In the case of magnetized WDs,the magnetic fields may disrupt the inner regions of the accretion disk,funnel the accretion flow onto the polar caps and even confine helium burning within the caps.We find that,for WDs with sufficiently strong magnetic fields,the parameter space of the potential SN Ia progenitor systems shrinks toward shorter orbital periods and lower donor masses compared with that in the non-magnetized WD case.The reason is that the magnetic confinement usually works with relatively high mass transfer rates,which can trigger strong wind mass loss from the WD,thus limiting the He-rich mass accumulation efficiency.The surviving companion stars are likely of low-mass at the moment of the SN explosions,which can be regarded as a possible explanation for the non-detection of surviving companions after the SNe or inside the SN remnants.However,the corresponding birthrate of Galactic SNe Ia in our high-magnetic models is estimated to be~(0.08–0.13)×10^(-3)yr^(-1)(~0.17–0.28×10^(-3)yr^(-1)for the non-magnetic models),significantly lower than the observed Galactic SN Ia birthrate.展开更多
I use recent observations of circumstellar matter(CSM)around type Ia supernovae(SNe Ia)to estimate the fraction of SNe Ia that explode into a planetary nebula(PN)and to suggest a new delay time distribution from the c...I use recent observations of circumstellar matter(CSM)around type Ia supernovae(SNe Ia)to estimate the fraction of SNe Ia that explode into a planetary nebula(PN)and to suggest a new delay time distribution from the common envelope evolution(CEE)to the SN Ia explosion for SNe Ia that occur shortly after the CEE.Under the assumption that the CSM results from a CEE,I crudely estimate that about 50%of all SNe Ia are SNe Ia inside PNe(SNIPs),and that the explosions of most SNIPs occur within a CEE to explosion delay(CEED)time of less than about ten thousand years.I also estimate that the explosion rate of SNIPs,i.e.,the CEED time distribution,is roughly constant within this timescale of ten thousand years.The short CEED time suggests that a fraction of SNIPs come from the core-degenerate(CD)scenario where the merger of the core with the white dwarf takes place at the end of the CEE.I present my view that the majority of SNIPs come from the CD scenario.I list some further observations that might support or reject my claims,and describe the challenge to theoretical studies to find a process to explain a merger to explosion delay(MED)time of up to ten thousand years or so.A long MED will apply also to the double degenerate scenario.展开更多
I study the possibility that within the frame of the core degenerate(CD)scenario for type Ia supernovae(SNe Ia)the merger process of the core of the asymptotic giant branch(AGB)star and the white dwarf(WD)maintains an...I study the possibility that within the frame of the core degenerate(CD)scenario for type Ia supernovae(SNe Ia)the merger process of the core of the asymptotic giant branch(AGB)star and the white dwarf(WD)maintains an envelope mass of≈0.03 Mthat causes a later helium shell flash.I estimate the number of pre-explosion helium shell flash events to be less than a few per cent of all CD scenario SNe Ia.A helium shell flash while the star moves to the left on the HR diagram as a post-AGB star(late thermal pulse—LTP)or along the WD cooling track(very LTP—VLTP)causes the star to expand and become a“born again”AGB star.Merger remnants exploding while still on the AGB form hydrogen-polluted peculiar SNe Ia,while an explosion inside an inflated born-again star results in an early flux excess in the light curve of the SN Ia.The fraction of systems that might show an early flux excess due to LTP/VLTP is<few×10^(-4) of all SNe Ia,much below the observed fraction.In the frame of the CD scenario SNe Ia with early flux excess result from SN ejecta collision with planetary nebula fallback gas,or from mixing of ^(56) Ni to the outer regions of the SN ejecta.Ongoing sky surveys might find about one case per year where LTP/VLTP influences the SN light curve.展开更多
In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST ...In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST database and applied them to train the machine learning process.Following the recognition procedure, we chose 351 DB spectra of 287 objects, 53 of which were new identifications. We then utilized all the DBWD spectra from both SDSS DR14 and LAMOST DR5 to construct DB templates for LAMOST 1 D pipeline reductions. Finally, by applying DB parameter models provided by D. Koester and the distance from Gaia DR2, we calculated the effective temperatures, surface gravities and distributions of the 3 D locations and velocities of all DBWDs.展开更多
A significant number of double white dwarfs(DWDs)are believed to merge within the Hubble time due to the gravitational wave(GW)emission during their inspiraling phase.The outcome of a DWD system is either a type Ia Su...A significant number of double white dwarfs(DWDs)are believed to merge within the Hubble time due to the gravitational wave(GW)emission during their inspiraling phase.The outcome of a DWD system is either a type Ia Supernova as the double-degenerate model,or a massive,long-lasting merger remnant.Expected multi-messenger signals of these events will help us to distinguish detailed merging physical processes.In this work,we aim to provide a generic scenario of DWD merging,investigate the emission of all major messengers,with a focus on GWs and neutrinos.Our goal is to provide some guidance for current and future(collaborative)efforts of multimessenger observations.Throughout the merging evolution of a DWD system,different messengers(GW,neutrino and electromagnetic wave)will dominate at different times.In this work,we show that DWD merger events located at the distance of 1 kpc can indeed produce detectable signals of GWs and neutrinos.The GW frequency is in 0.3–0.6 Hz band around 10 days before tidal disruption begins.We estimate that in optimistic situations,the neutrino number detected by upcoming detectors such as JUNO and Hyper-Kamiokande can reach O(1)for a DWD merging event at~1 kpc.展开更多
As one of the most useful cosmological distance indicators,type Ia supernovae(SNe Ia)play an important role in the study of cosmology.However,the progenitors of SNe Ia are still uncertain.It has been suggested that ca...As one of the most useful cosmological distance indicators,type Ia supernovae(SNe Ia)play an important role in the study of cosmology.However,the progenitors of SNe Ia are still uncertain.It has been suggested that carbonoxygen white dwarf(CO WD)+He subgiant systems could produce SNe Ia through the double-degenerate(DD)model,in which the He subgiant transfers He-rich matter to the primary CO WD and finally evolves to another CO WD.Recently,a CO WD+He star system(i.e.,HD 265435)has been discovered to be a new SNe Ia progenitor candidate based on the DD model.The orbital period of the system is about 0.0688 days,and the masses of the CO WD and the He star are 1.01±0.15 M_(⊙) and 0.63_(-0.12)^(+0.13)M_(⊙),respectively.In this work,we evolve a large number of primordial binaries to the formation of CO WD+He star systems and investigate the evolutionary history of HD265435.We find that HD 265435 may originate from a primordial binary that has a 5.18 M_(⊙) primary and a3.66 M_(⊙) secondary with an initial orbital period of 5200 days.The CO WD+He star system would be formed after the primordial binary experiences two common-envelope ejection processes.We also find that HD 265435 would evolve to a double WD system with a total mass of 1.58 M⊙after a stable mass-transfer process,and the double WD system would merge driven by gravitational wave radiation.We estimate that it would take about 76 Myr for HD 265435 to form an SN Ia.In addition,HD 265435 would be a potential target of space-based gravitational wave observatories(e.g.,LISA,Taiji and TianQin).展开更多
The binary systems consisting of a Be star and a white dwarf(Be WDs) are very interesting.They can originate from the binaries composed of a Be star and a subdwarf O or B star(Besd OBs),and they can merge into red gia...The binary systems consisting of a Be star and a white dwarf(Be WDs) are very interesting.They can originate from the binaries composed of a Be star and a subdwarf O or B star(Besd OBs),and they can merge into red giants via luminous red nova or can evolve into double WD potentially detected by the LISA mission.Using the method of population synthesis,we investigate the formation and the destiny of Be WDs,and discuss the effects of the metallicity(Z) and the common envelope evolution parameters.We find that Besd OBs are significant progenitors of Be WDs.About 30%(Z = 0.0001)-50%(Z = 0.02) of Be WDs come from Besd OBs.About 60%(Z = 0.0001)-70%(Z = 0.02) of Be WDs turn into red giants via a merger between a WD and a non-degenerated star.About 30%(Z = 0.0001)-40%(Z = 0.02) of Be WDs evolve into double WDs which are potential gravitational waves of the LISA mission at a frequency band between about 3 × 10^(-3)and 3 × 10^(-2)Hz.The common envelope evolution parameter introduces an uncertainty with a factor of about 1.3 on Be WD populations in our simulations.展开更多
The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the yea...The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams （CMDs） and spatial appearances have been created using 10 filters associated with the FUV channel （130-180 nm） and NUV channel （200-300 nm） that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.展开更多
Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation.However,a significant fraction with low mass ratios will survive for a long time as a conseque...Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation.However,a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass transfer.Such stable mass transfer between two helium white dwarfs（He WDs） provides one channel for the production of AM CVn binary stars.In previous calculations of double He WD progenitors,the accreting He WD was treated as a point mass.We have computed the evolution of 16 double He WD models in order to investigate the consequences of treating the evolution of both components in detail.We find that the boundary between binaries having stable and unstable mass transfer is slightly modified by this approach.By comparing with observed periods and mass ratios,we redetermine masses of eight known AM CVn stars by our double He WDs channel,i.e.HM Cnc,AM CVn,V406 Hya,J0926,J1240,GP Com,Gaia14 aae and V396 Hya.We propose that central spikes in the triple-peaked emission spectra of J1240,GP Com and V396 Hya and the surface abundance ratios of N/C/O in GP Com can be explained by the stable double He WD channel.The mass estimates derived from our calculations are used to discuss the predicted gravitational wave signal in the context of the Laser Interferometer Space Antenna（LISA） project.展开更多
The equation of state of the electron degenerate gas in a white dwarf is usually treated by employing the ideal dispersion relation.However, the effect of quantum gravity is expected to be inevitably present and when ...The equation of state of the electron degenerate gas in a white dwarf is usually treated by employing the ideal dispersion relation.However, the effect of quantum gravity is expected to be inevitably present and when this effect is considered through a non-commutative formulation, the dispersion relation undergoes a substantial modification.In this paper, we take such a modified dispersion relation and find the corresponding equation of state for the degenerate electron gas in white dwarfs.Hence we solve the equation of hydrostatic equilibrium and find that this leads to the possibility of the existence of excessively high values of masses exceeding the Chandrasekhar limit, although the quantum gravity effect is taken to be very small.It is only when we impose the additional effect of neutronization that we obtain white dwarfs with masses close to the Chandrasekhar limit with nonzero radii at the neutronization threshold.We demonstrate these results by giving numerical estimates for the masses and radii of helium, carbon and oxygen white dwarfs.展开更多
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 discuss...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.展开更多
We present GalevNB （Galev for N-body simulations）, a utility that converts fundamental stellar properties of N-body simulations into observational properties using the GALEV （GAlaxy EVolutionary synthesis models） ...We present GalevNB （Galev for N-body simulations）, a utility that converts fundamental stellar properties of N-body simulations into observational properties using the GALEV （GAlaxy EVolutionary synthesis models） package, and allowing direct comparisons between observations and N-body simulations. It works by converting fundamental stellar properties, such as stellar mass, temperature, luminosity and metallicity into observational magnitudes for a variety of filters used by mainstream instruments/telescopes, such as HST, ESO, SDSS, 2MASS, etc., and into spectra that span the range from far-UV （90 A） to near-IR （160 ~tm）. As an application, we use Ga 1 evNB to investigate the secular evolution of the spectral energy distribution （SED） and color magnitude diagram （CMD） of a simulated star cluster over a few hundred million years. With the results given by GalevNB we discover a UV-excess in the SED of the cluster over the whole simulation time. We also identify four candidates that contribute to the FUV peak： core helium burning stars, second asymptotic giant branch （AGB） stars, white dwarfs and naked helium stars.展开更多
Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite the highly successful use of these events...Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite the highly successful use of these events in this capacity, many fundamental questions remain. Contemporary research inves- tigates how properties of the progenitor system that follow from the host galaxy such as composition and age influence the brightness of an event with the goal of better understanding and assessing the intrinsic scatter in the brightness. We provide an overview of these supernovae and proposed progenitor systems, all of which involve one or more compact stars known as white dwarfs. We describe contemporary research investigating how the composition and structure of the progenitor white dwarf systematically influences the explosion outcome assuming the progenitor is a single white dwarf that has gained mass from a companion. We present results illustrating some of these systematic effects from our research.展开更多
We show that, by appealing to a Quark-Nova （QN） in a tight binary system containing a massive neutron star and a CO white dwarf （WD）, a Type Ia explosion could occur. The QN ejecta collides with the WD, driving a ...We show that, by appealing to a Quark-Nova （QN） in a tight binary system containing a massive neutron star and a CO white dwarf （WD）, a Type Ia explosion could occur. The QN ejecta collides with the WD, driving a shock that triggers carbon burning under degenerate conditions （the QN-Ia）. The conditions in the compressed low-mass WD （MwD 〈 0.9 M） in our model mimic those of a Chandrasekhar mass WD. The spin-down luminosity from the QN compact remnant （the quark star） pro- vides additional power that makes the QN-Ia light-curve brighter and broader than a standard SN-Ia with similar 56Ni yield. In QNe-Ia, photometry and spectroscopy are not necessarily linked since the kinetic energy of the ejecta has a contribution from spin-down power and nuclear decay. Although QNe-Ia may not obey the Phillips relationship, their brightness and their relatively ＂normal looking＂ light-curves mean they could be included in the cosmological sample. Light-curve fitters would be con- fused by the discrepancy between spectroscopy at peak and photometry and would correct for it by effectively brightening or dimming the QNe-Ia apparent magnitudes, thus over- or under-estimating the true magnitude of these spin-down powered SNe-Ia. Contamination of QNe-Ia in samples of SNe-Ia used for cosmological analyses could systematically bias measurements of cosmological parameters if QNe-Ia are numerous enough at high-redshift. The strong mixing induced by spin-down wind combined with the low 56Ni yields in QNe-Ia means that these would lack a secondary maximum in the/-band despite their luminous nature. We discuss possible QNe-Ia progenitors.展开更多
This article reviews the current works on ultra-compact double-degenerate binaries in the presence of magnetic interaction, in particular, unipolar induction. The orbital dynamics and evolution of compact white-dwarf ...This article reviews the current works on ultra-compact double-degenerate binaries in the presence of magnetic interaction, in particular, unipolar induction. The orbital dynamics and evolution of compact white-dwarf pairs are discussed in detail. Models and predictions of electron cyclotron masers from unipolar-inductor compact binaries and unipolar-inductor white-dwarf planetary systems are presented. Einstein-Laub effects in compact binaries are briefly discussed.展开更多
In the single degenerate （SD） scenario for type Ia supernovae （SNe Ia）, a mass-accreting white dwarf is expected to experience a supersoft X-ray source （SSS） phase. However, some recent observations showed that ...In the single degenerate （SD） scenario for type Ia supernovae （SNe Ia）, a mass-accreting white dwarf is expected to experience a supersoft X-ray source （SSS） phase. However, some recent observations showed that the expected number of massaccreting WDs is much lower than that predicted from theory, regardless of whether they are in spiral or elliptical galaxies. In this paper, we performed a binary population synthesis study on the relative duration of the SSS phase to their whole mass-increasing phase of WDs leading to SNe Ia. We found that for about 40% of the progenitor systems, the relative duration is shorter than 2% and the evolution of the mean relative duration shows that it is always smaller than 5%, both for young and old SNe Ia. In addition, before the SNe Ia explosions, more than 55% of the progenitor systems were experiencing a dwarf novae phase and no more than 10% were staying in the SSS phase. These results are consistent with the recent observations and imply that both in early- and late-type galaxies, only a small fraction of mass-accreting WDs resulting in SNe Ia contributes to the supersoft X-ray flux. So, although our results are not directly related to the X-ray output of the SN Ia progenitor, the low supersoft X- ray luminosity observed in early type galaxies may not be able to exclude the validity of the SD model. On the contrary, it is evidence to support the SD scenario.展开更多
We investigate the spectral evolution of white dwarfs by considering the effects of hydrogen mass in the atmosphere and convective overshooting above the convection zone. Our numerical results show that white dwarfs w...We investigate the spectral evolution of white dwarfs by considering the effects of hydrogen mass in the atmosphere and convective overshooting above the convection zone. Our numerical results show that white dwarfs with MH- 10^-16 MG show the DA spectral type between 46 000 ≤ Teff≤ 26 000 K and the DO or DB spectral type may appear on either side of this temperature range. White dwarfs with MH - 10^-15 M⊙ appear as DA stars until they cool to Teff - 31 000 K; from then on they will evolve into DB white dwarfs as a result of convective mixing. If MH in the white dwarfs is more than 10-14 M⊙, the convective mixing will not occur when Teff 〉 20 000 K, thus these white dwarfs always appear as DA stars. White dwarfs within the temperature range 46 000 ≤ Teff ≤ 31 000 K always show the DA spectral type, which coincides with the DB gap. We notice the importance of the convective overshooting and suggest that the overshooting length should be proportional to the thickness of the convection zone to better fit the observations.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12225304,12273105 and 11903075)the National Key R&D Program of China(Nos.2021YFA1600404,2021YFA1600403 and 2021YFA1600400)+5 种基金the Western Light Project of CAS(No.XBZG-ZDSYS-202117)the science research grants from the China Manned Space Project(No.CMS-CSST-2021-A12)the Youth Innovation Promotion Association CAS(No.2021058)the Yunnan Fundamental Research Projects(Nos.202001AS070029,202001AU070054,202101AT070027,202101AW070047 and 202201BC070003)the Frontier Scientific Research Program of Deep Space Exploration Laboratory(No.2022-QYKYJH-ZYTS-016)International Centre of Supernovae,Yunnan Key Laboratory(No.202302AN360001)。
文摘TypeⅠa supernovae(SNe Ia)are among the most energetic events in the universe.They are excellent cosmological distance indicators due to the remarkable homogeneity of their light curves.However,the nature of the progenitors of SNeⅠa is still not well understood.In the single-degenerate model,a carbon-oxygen white dwarf(CO WD)could grow its mass by accreting material from an asymptotic giant branch(AGB)star,leading to the formation of SNe Ia when the mass of the WD approaches to the Chandrasekhar-mass limit,known as the AGB donor channel.In this channel,previous studies mainly concentrate on the wind-accretion pathway for the mass-increase of the WDs.In the present work,we employed an integrated mass-transfer prescription for the semidetached WD+AGB systems,and evolved a number of WD+AGB systems for the formation of SNe Ia through the Roche-lobe overflow process or the wind-accretion process.We provided the initial and final parameter spaces of WD+AGB systems for producing SNe Ia.We also obtained the density distribution of circumstellar matter at the moment when the WD mass reaches the Chandrasekhar-mass limit.Moreover,we found that the massive WD+AGB sample AT 2019qyl can be covered by the final parameter space for producing SNe Ia,indicating that AT 2019qyl is a strong progenitor candidate of SNe Ia with AGB donors.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)the National Natural Science Foundation of China(NSFC,Grant No.12173104)+2 种基金the fellowship of China Postdoctoral Science Foundation(Grant No.2021M703769)the Natural Science Foundation of Guangdong Province of China(Grant No.2022A1515011862)the support by National Supercomputer Center in Guangzhou。
文摘The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way.However,the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation.In this paper,we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data.To quickly determine the rough parameters of the target sources,the following algorithms are adopted in a coarse search process:(1)using the downsampling method to reduce the number of original data points;(2)using the undersampling method to speed up the generation of a single waveform template;(3)using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space;(4)combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template.A fine search process is applied to further determine the parameters of the signals based on the coarse search,for which we adopt the particle swarm optimization.Finally,we detect O(10^(4))double white dwarf signals,validating the feasibility of our method.
基金supported by the Natural Science Foundation of China(Grant Nos.11773015,12121003,12041301)Project U1838201 supported by NSFC and CAS。
文摘The white dwarf(WD)+helium(He)star binary channel plays an important role in the single degenerate scenario for the progenitors of type Ia supernovae(SNe Ia).Previous studies on the WD+main sequence star evolution have shown that the magnetic fields of WDs may significantly influence their accretion and nuclear burning processes.In this work we focus on the evolution of magnetized WD+He star binaries with detailed stellar evolution and binary population synthesis(BPS)calculations.In the case of magnetized WDs,the magnetic fields may disrupt the inner regions of the accretion disk,funnel the accretion flow onto the polar caps and even confine helium burning within the caps.We find that,for WDs with sufficiently strong magnetic fields,the parameter space of the potential SN Ia progenitor systems shrinks toward shorter orbital periods and lower donor masses compared with that in the non-magnetized WD case.The reason is that the magnetic confinement usually works with relatively high mass transfer rates,which can trigger strong wind mass loss from the WD,thus limiting the He-rich mass accumulation efficiency.The surviving companion stars are likely of low-mass at the moment of the SN explosions,which can be regarded as a possible explanation for the non-detection of surviving companions after the SNe or inside the SN remnants.However,the corresponding birthrate of Galactic SNe Ia in our high-magnetic models is estimated to be~(0.08–0.13)×10^(-3)yr^(-1)(~0.17–0.28×10^(-3)yr^(-1)for the non-magnetic models),significantly lower than the observed Galactic SN Ia birthrate.
基金supported by a grant from the Israel Science Foundation(769/20)。
文摘I use recent observations of circumstellar matter(CSM)around type Ia supernovae(SNe Ia)to estimate the fraction of SNe Ia that explode into a planetary nebula(PN)and to suggest a new delay time distribution from the common envelope evolution(CEE)to the SN Ia explosion for SNe Ia that occur shortly after the CEE.Under the assumption that the CSM results from a CEE,I crudely estimate that about 50%of all SNe Ia are SNe Ia inside PNe(SNIPs),and that the explosions of most SNIPs occur within a CEE to explosion delay(CEED)time of less than about ten thousand years.I also estimate that the explosion rate of SNIPs,i.e.,the CEED time distribution,is roughly constant within this timescale of ten thousand years.The short CEED time suggests that a fraction of SNIPs come from the core-degenerate(CD)scenario where the merger of the core with the white dwarf takes place at the end of the CEE.I present my view that the majority of SNIPs come from the CD scenario.I list some further observations that might support or reject my claims,and describe the challenge to theoretical studies to find a process to explain a merger to explosion delay(MED)time of up to ten thousand years or so.A long MED will apply also to the double degenerate scenario.
基金supported by a grant from the Israel Science Foundation (769/20)。
文摘I study the possibility that within the frame of the core degenerate(CD)scenario for type Ia supernovae(SNe Ia)the merger process of the core of the asymptotic giant branch(AGB)star and the white dwarf(WD)maintains an envelope mass of≈0.03 Mthat causes a later helium shell flash.I estimate the number of pre-explosion helium shell flash events to be less than a few per cent of all CD scenario SNe Ia.A helium shell flash while the star moves to the left on the HR diagram as a post-AGB star(late thermal pulse—LTP)or along the WD cooling track(very LTP—VLTP)causes the star to expand and become a“born again”AGB star.Merger remnants exploding while still on the AGB form hydrogen-polluted peculiar SNe Ia,while an explosion inside an inflated born-again star results in an early flux excess in the light curve of the SN Ia.The fraction of systems that might show an early flux excess due to LTP/VLTP is<few×10^(-4) of all SNe Ia,much below the observed fraction.In the frame of the CD scenario SNe Ia with early flux excess result from SN ejecta collision with planetary nebula fallback gas,or from mixing of ^(56) Ni to the outer regions of the SN ejecta.Ongoing sky surveys might find about one case per year where LTP/VLTP influences the SN light curve.
基金funded by the National Basic Research Program of China (973 program, 2014CB845700)the National Natural Science Foundation of China (Grant No. 11390371/4)+1 种基金The Guo Shou Jing Telescope (the Large Sky Area Multiobject Fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission
文摘In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST database and applied them to train the machine learning process.Following the recognition procedure, we chose 351 DB spectra of 287 objects, 53 of which were new identifications. We then utilized all the DBWD spectra from both SDSS DR14 and LAMOST DR5 to construct DB templates for LAMOST 1 D pipeline reductions. Finally, by applying DB parameter models provided by D. Koester and the distance from Gaia DR2, we calculated the effective temperatures, surface gravities and distributions of the 3 D locations and velocities of all DBWDs.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11633007,12005313 and U1731136)Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)+1 种基金Key Laboratory of TianQin Project(Sun Yat-sen University)of the Ministry of Educationthe China Manned Space Project(No.CMS-CSST-2021-B09)。
文摘A significant number of double white dwarfs(DWDs)are believed to merge within the Hubble time due to the gravitational wave(GW)emission during their inspiraling phase.The outcome of a DWD system is either a type Ia Supernova as the double-degenerate model,or a massive,long-lasting merger remnant.Expected multi-messenger signals of these events will help us to distinguish detailed merging physical processes.In this work,we aim to provide a generic scenario of DWD merging,investigate the emission of all major messengers,with a focus on GWs and neutrinos.Our goal is to provide some guidance for current and future(collaborative)efforts of multimessenger observations.Throughout the merging evolution of a DWD system,different messengers(GW,neutrino and electromagnetic wave)will dominate at different times.In this work,we show that DWD merger events located at the distance of 1 kpc can indeed produce detectable signals of GWs and neutrinos.The GW frequency is in 0.3–0.6 Hz band around 10 days before tidal disruption begins.We estimate that in optimistic situations,the neutrino number detected by upcoming detectors such as JUNO and Hyper-Kamiokande can reach O(1)for a DWD merging event at~1 kpc.
基金supported by the National Key R&D Program of China(Nos.2021YFA1600404 and 2021YFA1600403)the National Natural Science Foundation of China(Nos.12225304 and 12273105)+3 种基金the Western Light Project of CAS(No.XBZG-ZDSYS-202117)the science research grants from the China Manned Space Project(Nos.CMS-CSST-2021-A12/B07)the Youth Innovation Promotion Association CAS(No.2021058)the Yunnan Fundamental Research Projects(Nos.202001AS070029,202001AU070054,202101AT070027 and 202101AW070047)。
文摘As one of the most useful cosmological distance indicators,type Ia supernovae(SNe Ia)play an important role in the study of cosmology.However,the progenitors of SNe Ia are still uncertain.It has been suggested that carbonoxygen white dwarf(CO WD)+He subgiant systems could produce SNe Ia through the double-degenerate(DD)model,in which the He subgiant transfers He-rich matter to the primary CO WD and finally evolves to another CO WD.Recently,a CO WD+He star system(i.e.,HD 265435)has been discovered to be a new SNe Ia progenitor candidate based on the DD model.The orbital period of the system is about 0.0688 days,and the masses of the CO WD and the He star are 1.01±0.15 M_(⊙) and 0.63_(-0.12)^(+0.13)M_(⊙),respectively.In this work,we evolve a large number of primordial binaries to the formation of CO WD+He star systems and investigate the evolutionary history of HD265435.We find that HD 265435 may originate from a primordial binary that has a 5.18 M_(⊙) primary and a3.66 M_(⊙) secondary with an initial orbital period of 5200 days.The CO WD+He star system would be formed after the primordial binary experiences two common-envelope ejection processes.We also find that HD 265435 would evolve to a double WD system with a total mass of 1.58 M⊙after a stable mass-transfer process,and the double WD system would merge driven by gravitational wave radiation.We estimate that it would take about 76 Myr for HD 265435 to form an SN Ia.In addition,HD 265435 would be a potential target of space-based gravitational wave observatories(e.g.,LISA,Taiji and TianQin).
基金the generous support of the Natural Science Foundation of Xinjiang No.2021D01C075the National Natural Science Foundation of China+1 种基金project Nos.12163005,U2031204 and 11863005the science research grants from the China Manned Space Project with No.CMSCSST-2021-A10。
文摘The binary systems consisting of a Be star and a white dwarf(Be WDs) are very interesting.They can originate from the binaries composed of a Be star and a subdwarf O or B star(Besd OBs),and they can merge into red giants via luminous red nova or can evolve into double WD potentially detected by the LISA mission.Using the method of population synthesis,we investigate the formation and the destiny of Be WDs,and discuss the effects of the metallicity(Z) and the common envelope evolution parameters.We find that Besd OBs are significant progenitors of Be WDs.About 30%(Z = 0.0001)-50%(Z = 0.02) of Be WDs come from Besd OBs.About 60%(Z = 0.0001)-70%(Z = 0.02) of Be WDs turn into red giants via a merger between a WD and a non-degenerated star.About 30%(Z = 0.0001)-40%(Z = 0.02) of Be WDs evolve into double WDs which are potential gravitational waves of the LISA mission at a frequency band between about 3 × 10^(-3)and 3 × 10^(-2)Hz.The common envelope evolution parameter introduces an uncertainty with a factor of about 1.3 on Be WD populations in our simulations.
文摘The Ultra Violet Imaging Telescope （UVIT） is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation （ISRO） in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams （CMDs） and spatial appearances have been created using 10 filters associated with the FUV channel （130-180 nm） and NUV channel （200-300 nm） that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.
基金supported by the CAS ‘Light of West China’ program(2015-XBQNA-02)the National Natural Science Foundation of China(NSFC,Grant Nos.10933002,11703001 and 11273007)+5 种基金the Joint Research Fund in Astronomy(U1631236) under cooperative agreement between the NSFC and the Chinese Academy of Sciences(CAS)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB2304100)the China Postdoctoral Science Foundationthe Fundamental Research Funds for the Central UniversitiesThe Armagh Observatory and Planetarium are supported by a grant from the Northern Ireland Department for Communitiessupport from the UK Science and Technology Facilities Council(STFC)(Grant No.ST/M000834/1)
文摘Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation.However,a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass transfer.Such stable mass transfer between two helium white dwarfs（He WDs） provides one channel for the production of AM CVn binary stars.In previous calculations of double He WD progenitors,the accreting He WD was treated as a point mass.We have computed the evolution of 16 double He WD models in order to investigate the consequences of treating the evolution of both components in detail.We find that the boundary between binaries having stable and unstable mass transfer is slightly modified by this approach.By comparing with observed periods and mass ratios,we redetermine masses of eight known AM CVn stars by our double He WDs channel,i.e.HM Cnc,AM CVn,V406 Hya,J0926,J1240,GP Com,Gaia14 aae and V396 Hya.We propose that central spikes in the triple-peaked emission spectra of J1240,GP Com and V396 Hya and the surface abundance ratios of N/C/O in GP Com can be explained by the stable double He WD channel.The mass estimates derived from our calculations are used to discuss the predicted gravitational wave signal in the context of the Laser Interferometer Space Antenna（LISA） project.
基金the Ministry of Human Resource Development, Government of India, for financial support through a doctoral fellowship
文摘The equation of state of the electron degenerate gas in a white dwarf is usually treated by employing the ideal dispersion relation.However, the effect of quantum gravity is expected to be inevitably present and when this effect is considered through a non-commutative formulation, the dispersion relation undergoes a substantial modification.In this paper, we take such a modified dispersion relation and find the corresponding equation of state for the degenerate electron gas in white dwarfs.Hence we solve the equation of hydrostatic equilibrium and find that this leads to the possibility of the existence of excessively high values of masses exceeding the Chandrasekhar limit, although the quantum gravity effect is taken to be very small.It is only when we impose the additional effect of neutronization that we obtain white dwarfs with masses close to the Chandrasekhar limit with nonzero radii at the neutronization threshold.We demonstrate these results by giving numerical estimates for the masses and radii of helium, carbon and oxygen white dwarfs.
基金the National Natural Science Foundation of China(Grant Nos.11965010 and 11565020)the Natural Science Foundation of Hainan Province(Grant Nos.2019RC239,118MS071 and 114012)+2 种基金the Counterpart Foundation of Sanya(Grant 2016PT43 and 2019PT76)the Special Foundation of Science and Technology Cooperation for Advanced Academy and Regional of Sanya(Grant 2016YD28)the Scientific Research Starting Foundation for 515 Talented Project of Hainan Tropical Ocean University(Grant RHDRC201701)。
文摘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.
基金funded by the National Natural Science Foundation of China,Nos.11443001(XYP)and 11073025(RS)the funds of the National Natural Science Foundation of China,No.11503015+11 种基金Shanghai education committee,No.1021ZK 151009027-ZZyy 15104the talents introduction project of the Shanghai Institute of Technology,No.10120K156031-YJ 2014-05the Silk Road Project Team based at National Astronomical Observatories,Chinese Academy of Sciences(NAOC,http://silkroad.bao.ac.cn)funding by the German Research Foundation(DFG)grant OL 350/1-1partly supported through computational resources of SFB 881“The Milky Way System”(subproject Z2)at the University of Heidelberg,Germany,in particular the Milky Way supercomputer hosted and co-funded by the Jülich Supercomputing Center(JSC)the travel grants of the DFG grant OL 350/1-1support by the Chinese Academy of Sciences Visiting Professorship for Senior International Scientists,Grant Number 2009S1-5the“Qianren”special foreign experts program of China,both at NAOCfunded by the Ministry of Finance of the People’s Republic of China under the grant ZDY Z2008-2,has been used for simulations,as well as the smaller GPU clusters titan,hydra and keplerfunded under the grants I/80041-043 and I/84678/84680 of the Volkswagen Foundation at ARI/ZAH,University of Heidelberg,Germanyfinancial support from the National Science Foundation under Grant No.1412449STScI theory grant HST-AR12840.01-A
文摘We present GalevNB （Galev for N-body simulations）, a utility that converts fundamental stellar properties of N-body simulations into observational properties using the GALEV （GAlaxy EVolutionary synthesis models） package, and allowing direct comparisons between observations and N-body simulations. It works by converting fundamental stellar properties, such as stellar mass, temperature, luminosity and metallicity into observational magnitudes for a variety of filters used by mainstream instruments/telescopes, such as HST, ESO, SDSS, 2MASS, etc., and into spectra that span the range from far-UV （90 A） to near-IR （160 ~tm）. As an application, we use Ga 1 evNB to investigate the secular evolution of the spectral energy distribution （SED） and color magnitude diagram （CMD） of a simulated star cluster over a few hundred million years. With the results given by GalevNB we discover a UV-excess in the SED of the cluster over the whole simulation time. We also identify four candidates that contribute to the FUV peak： core helium burning stars, second asymptotic giant branch （AGB） stars, white dwarfs and naked helium stars.
文摘Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite the highly successful use of these events in this capacity, many fundamental questions remain. Contemporary research inves- tigates how properties of the progenitor system that follow from the host galaxy such as composition and age influence the brightness of an event with the goal of better understanding and assessing the intrinsic scatter in the brightness. We provide an overview of these supernovae and proposed progenitor systems, all of which involve one or more compact stars known as white dwarfs. We describe contemporary research investigating how the composition and structure of the progenitor white dwarf systematically influences the explosion outcome assuming the progenitor is a single white dwarf that has gained mass from a companion. We present results illustrating some of these systematic effects from our research.
文摘We show that, by appealing to a Quark-Nova （QN） in a tight binary system containing a massive neutron star and a CO white dwarf （WD）, a Type Ia explosion could occur. The QN ejecta collides with the WD, driving a shock that triggers carbon burning under degenerate conditions （the QN-Ia）. The conditions in the compressed low-mass WD （MwD 〈 0.9 M） in our model mimic those of a Chandrasekhar mass WD. The spin-down luminosity from the QN compact remnant （the quark star） pro- vides additional power that makes the QN-Ia light-curve brighter and broader than a standard SN-Ia with similar 56Ni yield. In QNe-Ia, photometry and spectroscopy are not necessarily linked since the kinetic energy of the ejecta has a contribution from spin-down power and nuclear decay. Although QNe-Ia may not obey the Phillips relationship, their brightness and their relatively ＂normal looking＂ light-curves mean they could be included in the cosmological sample. Light-curve fitters would be con- fused by the discrepancy between spectroscopy at peak and photometry and would correct for it by effectively brightening or dimming the QNe-Ia apparent magnitudes, thus over- or under-estimating the true magnitude of these spin-down powered SNe-Ia. Contamination of QNe-Ia in samples of SNe-Ia used for cosmological analyses could systematically bias measurements of cosmological parameters if QNe-Ia are numerous enough at high-redshift. The strong mixing induced by spin-down wind combined with the low 56Ni yields in QNe-Ia means that these would lack a secondary maximum in the/-band despite their luminous nature. We discuss possible QNe-Ia progenitors.
文摘This article reviews the current works on ultra-compact double-degenerate binaries in the presence of magnetic interaction, in particular, unipolar induction. The orbital dynamics and evolution of compact white-dwarf pairs are discussed in detail. Models and predictions of electron cyclotron masers from unipolar-inductor compact binaries and unipolar-inductor white-dwarf planetary systems are presented. Einstein-Laub effects in compact binaries are briefly discussed.
基金supported by the National Natural Science Foundation of China under Grant No. 11003003the Project of the Fundamental and Frontier Research of Henan Province (102300410223)+1 种基金the Project of Science and Technology from the Ministry of Education (211102)the China Postdoctoral Science Foundation funded project 20100480222
文摘In the single degenerate （SD） scenario for type Ia supernovae （SNe Ia）, a mass-accreting white dwarf is expected to experience a supersoft X-ray source （SSS） phase. However, some recent observations showed that the expected number of massaccreting WDs is much lower than that predicted from theory, regardless of whether they are in spiral or elliptical galaxies. In this paper, we performed a binary population synthesis study on the relative duration of the SSS phase to their whole mass-increasing phase of WDs leading to SNe Ia. We found that for about 40% of the progenitor systems, the relative duration is shorter than 2% and the evolution of the mean relative duration shows that it is always smaller than 5%, both for young and old SNe Ia. In addition, before the SNe Ia explosions, more than 55% of the progenitor systems were experiencing a dwarf novae phase and no more than 10% were staying in the SSS phase. These results are consistent with the recent observations and imply that both in early- and late-type galaxies, only a small fraction of mass-accreting WDs resulting in SNe Ia contributes to the supersoft X-ray flux. So, although our results are not directly related to the X-ray output of the SN Ia progenitor, the low supersoft X- ray luminosity observed in early type galaxies may not be able to exclude the validity of the SD model. On the contrary, it is evidence to support the SD scenario.
基金supported by the National Key Fundamental Research Project through grant 2007CB815406
文摘We investigate the spectral evolution of white dwarfs by considering the effects of hydrogen mass in the atmosphere and convective overshooting above the convection zone. Our numerical results show that white dwarfs with MH- 10^-16 MG show the DA spectral type between 46 000 ≤ Teff≤ 26 000 K and the DO or DB spectral type may appear on either side of this temperature range. White dwarfs with MH - 10^-15 M⊙ appear as DA stars until they cool to Teff - 31 000 K; from then on they will evolve into DB white dwarfs as a result of convective mixing. If MH in the white dwarfs is more than 10-14 M⊙, the convective mixing will not occur when Teff 〉 20 000 K, thus these white dwarfs always appear as DA stars. White dwarfs within the temperature range 46 000 ≤ Teff ≤ 31 000 K always show the DA spectral type, which coincides with the DB gap. We notice the importance of the convective overshooting and suggest that the overshooting length should be proportional to the thickness of the convection zone to better fit the observations.
