This paper provides a method to study the solution of equations for syn- chronous binary stars with large eccentricity on the main sequence. The theoretical results show that the evolution of the eccentricity is linea...This paper provides a method to study the solution of equations for syn- chronous binary stars with large eccentricity on the main sequence. The theoretical results show that the evolution of the eccentricity is linear with time or follows an exponential form, and the semi-major axis and spin vary with time in an exponen- tial form that are different from the results given in a previous paper. The improved method is applicable in both cases of large eccentricity and small eccentricity. In ad- dition, the number of terms in the expansion of a series with small eccentricity is very long due to the series converging slowly. The advantage of this method is that it is applicable to cases with large eccentricity due to the series converging quickly. This paper chooses the synchronous binary star V1143 Cyg that is on the main sequence and has a large eccentricity （e = 0.54） as an example calculation and gives the nu- merical results. Lastly, the evolutionary tendency including the evolution of orbit and spin, the time for the speed up of spin, the circularization time, the orbital collapse time and the life time are given in the discussion and conclusion. The results shown in this paper are an improvement on those from the previous paper.展开更多
Three important physical processes occurring in contact binary systems are studied. The first one is the effect of spin, orbital rotation and tide on the structure of the components, which includes also the effect of ...Three important physical processes occurring in contact binary systems are studied. The first one is the effect of spin, orbital rotation and tide on the structure of the components, which includes also the effect of meridian circulation on the mixing of the chemical elements in the components. The second one is the mass and energy exchange between the components. To describe the energy exchange, a new approach is introduced based on the understanding that the exchange is due to the release of the potential, kinetic and thermal energy of the exchanged mass. The third is the loss of mass and angular momentum through the outer Lagrangian point. The rate of mass loss and the angular momentum carded away by the lost mass are discussed. To show the effects of these processes, we follow the evolution of a binary system consisting of a 12M⊙ and a 5M⊙ star with mass exchange between the components and mass loss via the outer Lagrangian point, both with and without considering the effects of rotation and tide. The result shows that the effect of rotation and tide advances the start of the semi-detached and the contact phases, and delays the end of the hydrogen-burning phase of the primary. Furthermore, it can change not only the occurrence of mass and angular momentum loss via the outer Lagrangian point, but also the contact or semi-contact status of the system. Thus, this effect can result in the special phenomenon of short-term variations occurring over a slow increase of the orbital period. The occurrence of mass and angular momentum loss via the outer Lagrangian point can affect the orbital period of the system significantly, but this process can be influenced, even suppressed out by the effect of rotation and tide. The mass and energy exchange occurs in the common envelope. The net result of the mass exchange process is a mass transfer from the primary to the secondary during the whole contact phase.展开更多
A model for contact binary systems is presented, which incorporates the following special features： a） The energy exchange between the components is based on the understanding that the energy exchange is due to the ...A model for contact binary systems is presented, which incorporates the following special features： a） The energy exchange between the components is based on the understanding that the energy exchange is due to the release of potential, kinetic and thermal energies of the exchanged mass. b） A special form of mass and angular momentum loss occurring in contact binaries is losses via the outer Lagrangian point, c） The effects of spin, orbital rotation and tidal action on the stellar structure as well as the effect of meridian circulation on the mixing of the chemical elements are considered, d） The model is valid not only for low-mass contact binaries but also for high-mass contact binaries. For illustration, we used the model to trace the evolution of a massive binary system consisting of one 12M⊙ and one 5M⊙ star. The result shows that the start and end of the contact stage fall within the semi-detached phase during which the primary continually transfers mass to the secondary. The time span of the contact stage is short and the mass transfer rate is very large. Therefore, the contact stage can be regarded as a special part of the semi-detached phase with a large mass transfer rate. Both mass loss through the outer Lagrangian point and oscillation between contact and semi-contact states can occur during the contact phase, and the effective temperatures of the primary and the secondary are almost equal.展开更多
Nova Sco 2008(=V1309 Sco)is an example of a V838 Mon type eruption rather than a typical classical nova.This enigmatic object was recently shown to have resulted from the merger of two stars in a contact binary.It is ...Nova Sco 2008(=V1309 Sco)is an example of a V838 Mon type eruption rather than a typical classical nova.This enigmatic object was recently shown to have resulted from the merger of two stars in a contact binary.It is the first stellar merger that was identified to be undergoing a common envelope transient.To understand the properties of its binary progenitor,the pre-outburst light curves were analyzed by using the W-D method.The photometric solution of the 2002 light curve shows that it is a deep contact binary(f=89.5(~40.5)%)with a mass ratio of 0.094.The asymmetry of the light curve is explained by the presence of a dark spot on the more massive component.The extremely high fill-out factor suggests that the merging of the contact binary is driven by dynamical mass loss from the outer Lagrange point.However,the analysis of the 2004 light curve indicates that no solutions were obtained even at an extremely low mass ratio of q=0.03.This suggests that the common convective envelope of the binary system disappeared and the secondary component spiraled into the envelope of the primary in 2004.Finally,the ejection of the envelope of the primary produced the outburst.展开更多
We perform numerical calculations to simulate the evolution of low-mass X-ray binary systems. For the accreting compact object we consider the initial mass of 1.4, 10, 20, 100, 200, 500 and 1000 Mo, corresponding to n...We perform numerical calculations to simulate the evolution of low-mass X-ray binary systems. For the accreting compact object we consider the initial mass of 1.4, 10, 20, 100, 200, 500 and 1000 Mo, corresponding to neutron stars （NSs）, stellar- mass black holes （BHs） and intermediate-mass BHs. Mass transfer in these binaries is driven by nuclear evolution of the donors and/or orbital angular momentum loss due to magnetic braking and gravitational wave radiation. For the different systems, we determine their bifurcation periods Pbif that separate the formation of converging systems from the diverging ones, and show that Pbif changes from ~ 1 d to ≥ 3 d for a 1 Mo donor star, with increasing initial accretor mass from 1.4 to 1000 Mo. This means that the dominant mechanism of orbital angular momentum loss changes from magnetic braking to gravitational radiation. As an illustration we compare the evolution of binaries consisting of a secondary star of 1 Mo at a fixed initial period of 2 d. In the case of the NS or stellar-mass BH accretor, the system evolves to a well-detached He white dwarf-neutron star/black hole pair, but it evolves to an ultra- compact binary if the compact object is an intermediate-mass BH. Thus the binary evolution heavily depends upon the mass of the compact object. However, we show that the final orbital period-white dwarf mass relation found for NS low-mass X-ray binaries is fairly insensitive to the initial mass of the accreting star, even if it is an intermediate-mass BH.展开更多
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period...We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the helium-rich matter in the center of the primary is mixed into the envelope, and there is little distinction in the evolutionary tracks of the mergers. The timescales of the mergers remaining on the main sequence, tBS are very similar (-6.2×108yr) if qmix< 0.71, since no hydrogen-rich matter of the secondary is mixed into the core of the mergers; for qmix > 0.71, the larger qmix is, the greater the mixing, hence the longer the blue straggler lifetime, tBS, and also the greater the luminosity. For qmix= 1.00, tBS -8.5×108yr. Estimation by (?)r - (?)a = 0.0 shows that the point at which tBS begins to increase is about qmix= 0.68. In comparison with the homogeneously mixed models, the merger with a helium profile similar to that of the primary is less luminous and has a shorter tBS.展开更多
The core-degenerate （CD） scenario has been suggested to be a possible progenitor model of type Ia supernovae （SNe Ia）, in which a carbon-oxygen white dwarf merges with the hot CO core of a massive asymptotic giant...The core-degenerate （CD） scenario has been suggested to be a possible progenitor model of type Ia supernovae （SNe Ia）, in which a carbon-oxygen white dwarf merges with the hot CO core of a massive asymptotic giant branch star dur- ing their common-envelope phase. However, the SN Ia birthrates for this scenario are still uncertain. We conducted a detailed investigation into the CD scenario and then gave the birthrates for this scenario using a detailed Monte Carlo binary pop- ulation synthesis approach. We found that the delay times of SNe Ia from this sce- nario are -70 Myr- 1400 Myr, which means that the CD scenario contributes to young SN Ia populations. The Galactic SN Ia birthrates for this scenario are in the range of ~7.4×10^-5 yr^-1- 3.7 × 10^-4 yr^-1, which roughly accounts for -2%-10% of all SNe Ia. This indicates that, under the assumptions made here, the CD scenario only contributes a small portion of all SNe Ia, which is not consistent with the results of Ilkov ＆ Soker.展开更多
Abstract The binding energy parameter A plays a vital role in common envelope evolution. Though it is well known that A takes different values for stars with different masses and varies during stellar evolution, it ha...Abstract The binding energy parameter A plays a vital role in common envelope evolution. Though it is well known that A takes different values for stars with different masses and varies during stellar evolution, it has been erroneously adopted as a constant in most population synthesis calculations. We have system- atically calculated the values of A for stars of masses 1 - 60 M by use of an updated stellar evolution code, taking into account the contribution from both gravitational energy and internal energy to the binding energy of the envelope. We adopt the criterion for the core-envelope boundary advocated by Ivanova. A new kind of A with an enthalpy prescription is also investigated. We present fitting formulae for the calculated values of various kinds of A, which can be used in future population synthesis studies.展开更多
The final outcomes of accreting ONe white dwarfs（ONe WDs） have been studied for several decades,but there are still some issues that are not resolved. Recently,some studies suggested that the deflagration of oxygen ...The final outcomes of accreting ONe white dwarfs（ONe WDs） have been studied for several decades,but there are still some issues that are not resolved. Recently,some studies suggested that the deflagration of oxygen would occur for accreting ONe WDs with Chandrasekhar masses. In this paper,we aim to investigate whether ONe WDs can experience accretion-induced collapse（AIC） or explosions when their masses approach the Chandrasekhar limit. Employing the stellar evolution code Modules for Experiments in Stellar Astrophysics（MESA）,we simulate the longterm evolution of ONe WDs with accreting CO material. The ONe WDs undergo weak multicycle carbon flashes during the mass-accretion process,leading to mass increase of the WDs. We found that different initial WD masses and mass-accretion rates influence the evolution of central density and temperature. However,the central temperature cannot reach the explosive oxygen ignition temperature due to neutrino cooling. This work implies that the final outcome of accreting ONe WDs is electroncapture induced collapse rather than thermonuclear explosion.展开更多
The single-degenerate(SD)model is one of the most popular progenitor models of type Ia supernovae(SNe Ia),in which the companion star can survive after an SN Ia explosion and show peculiar properties.Therefore,searchi...The single-degenerate(SD)model is one of the most popular progenitor models of type Ia supernovae(SNe Ia),in which the companion star can survive after an SN Ia explosion and show peculiar properties.Therefore,searching for the surviving companion in type Ia supernova remnants(SNRs)is a potential method to verify the SD model.In the SN 1604 remnant(Kepler’s SNR),although Chandra X-ray observation suggests that the progenitor is most likely a WD+AGB system,the surviving companion has not been found.One possible reason is rapid rotation of the white dwarf(WD),causing explosion of the WD to be delayed for a spin-down timescale,and then the companion evolved into a WD before the supernova explosion,so the companion is too dim to be detected.We aim to verify this possible explanation by carrying out binary evolution calculations.In this paper,we use Eggleton’s stellar evolution code to calculate the evolution of binaries consisting of a WD+red giant(RG).We assume that the rapidly rotating WD can continuously increase its mass when its mass exceeds the Chandrasekhar mass limit(MCh=1.378 M_⊙)until the mass-transfer rate decreases to be lower than a critical value.Eventually,we obtain the final masses of a WD in the range 1.378 M_⊙ to 2.707 M_⊙.We also show that if the spin-down time is less than 10~6yr,the companion star will be very bright and easily observed;but if the spin-down time is as long as^10~7 yr,the luminosities of the surviving companion would be lower than the detection limit.Our simulation provides guidance in hunting for the surviving companion stars in SNRs,and the fact that no surviving companion has been found in Kepler’s SNR may not be definite evidence disfavoring the SD origin of Kepler’s SN.展开更多
New three color light curves of TY Boo were acquired during five nights from February to May 2006 in the BVR bandpass using a 50-cm F/8.4 Ritchey- Chr6tien telescope （Ba50） at the Baja Astronomical Observatory （Hun...New three color light curves of TY Boo were acquired during five nights from February to May 2006 in the BVR bandpass using a 50-cm F/8.4 Ritchey- Chr6tien telescope （Ba50） at the Baja Astronomical Observatory （Hungary）, with a 512×512 Apogee AP-7 CCD camera. A photometric solution of these light curves was obtained by means of the Wilson-Devinney code. The results showed that the less massive component is hotter than the more massive one, and the temperature difference between the components is △T -249 K. Long term investigation of the system based on all available data shows two stages of increase and a similar trend for decrease, which appears to be periodic behavior. A set of new light elements yields a new period （P = 0.3171506d） and shows a periodic decrease with the rate dP/dE -- 5.858×10^-12 d cycle-1, 6.742×10^-9 d yr-1 or 0.058 s century-1. The evolutionary status of the system is discussed.展开更多
Type Ia supernovae （SNe Ia） play an important role in studies of cosmology and galactic chemi- cal evolution. They are believed to be thermonuclear explosions of carbon-oxygen white dwarfs （CO WDs） when their mass...Type Ia supernovae （SNe Ia） play an important role in studies of cosmology and galactic chemi- cal evolution. They are believed to be thermonuclear explosions of carbon-oxygen white dwarfs （CO WDs） when their masses approach the Chandrasekar （Ch） mass limit. However, it is still not completely under- stood how a CO WD increases its mass to the Ch-mass limit in the classical single-degenerate （SD） model. In this paper, we studied the mass accretion process in the SD model to examine whether the WD can explode as an SN Ia. Employing the stellar evolution code called modules for experiments in stellar as- trophysics （MESA）, we simulated the He accretion process onto CO WDs. We found that the WD can increase its mass to the Ch-mass limit through the SD model and explosive carbon ignition finally occurs in its center, which will lead to an SN Ia explosion. Our results imply that SNe Ia can be produced from the SD model through steady helium accretion. Moreover, this work can provide initial input parameters for explosion models of SNe Ia.展开更多
Grids of stellar evolution omy/astrophysics, such as planet hosting are required in many fields of astron- stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models w...Grids of stellar evolution omy/astrophysics, such as planet hosting are required in many fields of astron- stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models with updated ingredients and recently determined solar abundances is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough （0.01 M） that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00M. We present results in different forms of tables for easy and general appli- cation. The second stellar harmonic, required for analysis of apsidal motion of eclips- ing binaries, is also listed. We also construct rotating models to determine the effect of rotation on stellar structure and derive fitting formulae for luminosity, radius and the second harmonic as a function of rotational parameter. We also compute and list colors and bolometric corrections of models required for transformation between theo- retical and observational results. The results are tested for the Sun, the Hyades cluster, the slowly rotating chemically peculiar Am stars and eclipsing binaries with apsidal motion. The theoretical and observational results along isochrones are in good agree- ment. The grids are also applicable to rotating stars provided that equatorial velocity is given.展开更多
Although Type Ia supernovae （SNe Ia） play an important role in the study of cosmology, their progenitors are still poorly understood. Thermonuclear explosions from the helium double-detonation sub-Chandrasekhar mass...Although Type Ia supernovae （SNe Ia） play an important role in the study of cosmology, their progenitors are still poorly understood. Thermonuclear explosions from the helium double-detonation sub-Chandrasekhar mass model have been considered as an alternative method for producing SNe Ia. By adopting the assumption that a double detonation occurs when a He layer with a critical ignition mass accumulates on the surface of a carbon-oxygen white dwarf （CO WD）, we perform detailed binary evolution calculations for the He double-detonation model, in which a He layer from a He star accumulates on a CO WD. According to these calculations, we obtain the initial parameter spaces for SNe Ia in the orbital period and secondary mass plane for various initial WD masses. We implement these results into a detailed binary population synthesis approach to calculate SN Ia birthrates and delay times. From this model, the SN Ia birthrate in our Galaxy is ～0.4 - 1.6 × 10^-3 yr^-1. This indicates that the double-detonation model only produces part of the SNe la. The delay times from this model are ～ 70 - 710 Myr, which contribute to the young population of SNe Ia in the observations. We found that the CO WD ＋ sdB star system CD-30 11223 could produce an SN Ia via the double-detonation model in its future evolution.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
By simulating the evolution of spin periods of magnetized neutron stars which interact with their environment in binary systems,we investigate the Galactic population of high mass X-ray binaries（HMXBs） .The number o...By simulating the evolution of spin periods of magnetized neutron stars which interact with their environment in binary systems,we investigate the Galactic population of high mass X-ray binaries（HMXBs） .The number of HMXBs in the Galaxy is between 190 and 240,and their birthrate is from 5.9×10-5 yr-1 to 6.3× 10-5 yr-1.Comparing the Corbet diagram（the positions of the spin periods vs.the orbital periods of HMXBs） in our model with the associated observations,we find that the stellar wind structure and the process of matter transfer are very important for understanding HMXBs.展开更多
Type Ia supernovae （SNe Ia） play an important role in the study of cosmic evolution, especially in cosmology. There are several progenitor models for SNe Ia proposed in the past years. By considering the effect of a...Type Ia supernovae （SNe Ia） play an important role in the study of cosmic evolution, especially in cosmology. There are several progenitor models for SNe Ia proposed in the past years. By considering the effect of accretion disk instability on the evolution of white dwarf （WD） binaries, we performed detailed binary evolution calculations for the WD ＋ red-giant （RG） channel of SNe Ia, in which a carbon--oxygen WD accretes material from a RG star to increase its mass to the Chandrasekhar mass limit. According to these calculations, we mapped out the initial and final parameters for SNe Ia in the orbital period-secondary mass （log Pi_ M2^i） plane for various WD masses for this channel. We discussed the influence of the variation of the duty cycle value on the regions for producing SNe Ia. Similar to previous studies, this work also indicates that the long-period dwarf novae offer possible ways for producing SNe Ia. Meanwhile, we find that the surviving companion stars from this channel have a low mass after the SN explosion, which may provide a means for the formation of the population of single low-mass WDs （〈0.45 M⊙）.展开更多
Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow （...Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow （RLOF）. The RLOF can be divided into two cases： dynamically unstable and stable. In the first case, the birthrate of symbiotic stars is 0.056 yr^- 1 or 0.045 yr^-1 depending on different assumptions; in the stable RLOF case, it is 0.002 yr^-1 or 0.005yr^-1. The number of symbiotic stars with main-sequence accretors and unstable RLOF in our galaxy is about 5, that with stable RLOF is about 60 to 280. Comparison between our results with those of Yungelson et al. shows that symbiotic stars with MS accretors make only a small contribution （ ≤ 8%） to the whole population of symbiotic stars in the Galaxy.展开更多
文摘This paper provides a method to study the solution of equations for syn- chronous binary stars with large eccentricity on the main sequence. The theoretical results show that the evolution of the eccentricity is linear with time or follows an exponential form, and the semi-major axis and spin vary with time in an exponen- tial form that are different from the results given in a previous paper. The improved method is applicable in both cases of large eccentricity and small eccentricity. In ad- dition, the number of terms in the expansion of a series with small eccentricity is very long due to the series converging slowly. The advantage of this method is that it is applicable to cases with large eccentricity due to the series converging quickly. This paper chooses the synchronous binary star V1143 Cyg that is on the main sequence and has a large eccentricity （e = 0.54） as an example calculation and gives the nu- merical results. Lastly, the evolutionary tendency including the evolution of orbit and spin, the time for the speed up of spin, the circularization time, the orbital collapse time and the life time are given in the discussion and conclusion. The results shown in this paper are an improvement on those from the previous paper.
基金Supported by the National Natural Science Foundation of China.
文摘Three important physical processes occurring in contact binary systems are studied. The first one is the effect of spin, orbital rotation and tide on the structure of the components, which includes also the effect of meridian circulation on the mixing of the chemical elements in the components. The second one is the mass and energy exchange between the components. To describe the energy exchange, a new approach is introduced based on the understanding that the exchange is due to the release of the potential, kinetic and thermal energy of the exchanged mass. The third is the loss of mass and angular momentum through the outer Lagrangian point. The rate of mass loss and the angular momentum carded away by the lost mass are discussed. To show the effects of these processes, we follow the evolution of a binary system consisting of a 12M⊙ and a 5M⊙ star with mass exchange between the components and mass loss via the outer Lagrangian point, both with and without considering the effects of rotation and tide. The result shows that the effect of rotation and tide advances the start of the semi-detached and the contact phases, and delays the end of the hydrogen-burning phase of the primary. Furthermore, it can change not only the occurrence of mass and angular momentum loss via the outer Lagrangian point, but also the contact or semi-contact status of the system. Thus, this effect can result in the special phenomenon of short-term variations occurring over a slow increase of the orbital period. The occurrence of mass and angular momentum loss via the outer Lagrangian point can affect the orbital period of the system significantly, but this process can be influenced, even suppressed out by the effect of rotation and tide. The mass and energy exchange occurs in the common envelope. The net result of the mass exchange process is a mass transfer from the primary to the secondary during the whole contact phase.
基金the National Natural Science Foundation of China.
文摘A model for contact binary systems is presented, which incorporates the following special features： a） The energy exchange between the components is based on the understanding that the energy exchange is due to the release of potential, kinetic and thermal energies of the exchanged mass. b） A special form of mass and angular momentum loss occurring in contact binaries is losses via the outer Lagrangian point, c） The effects of spin, orbital rotation and tidal action on the stellar structure as well as the effect of meridian circulation on the mixing of the chemical elements are considered, d） The model is valid not only for low-mass contact binaries but also for high-mass contact binaries. For illustration, we used the model to trace the evolution of a massive binary system consisting of one 12M⊙ and one 5M⊙ star. The result shows that the start and end of the contact stage fall within the semi-detached phase during which the primary continually transfers mass to the secondary. The time span of the contact stage is short and the mass transfer rate is very large. Therefore, the contact stage can be regarded as a special part of the semi-detached phase with a large mass transfer rate. Both mass loss through the outer Lagrangian point and oscillation between contact and semi-contact states can occur during the contact phase, and the effective temperatures of the primary and the secondary are almost equal.
基金supported by the National Natural Science Foundation of China(Nos.11133007,11325315 and 11573063)the Key Research Program of the Chinese Academy of Sciences(Grant No.KGZD-EW-603)+1 种基金the Science Foundation of Yunnan Province(Nos.2012HC011 and 2013FB084)the Strategic Priority Research Program“The Emergence of Cosmological Structures”of the Chinese Academy of Sciences(No.XDB09010202)
文摘Nova Sco 2008(=V1309 Sco)is an example of a V838 Mon type eruption rather than a typical classical nova.This enigmatic object was recently shown to have resulted from the merger of two stars in a contact binary.It is the first stellar merger that was identified to be undergoing a common envelope transient.To understand the properties of its binary progenitor,the pre-outburst light curves were analyzed by using the W-D method.The photometric solution of the 2002 light curve shows that it is a deep contact binary(f=89.5(~40.5)%)with a mass ratio of 0.094.The asymmetry of the light curve is explained by the presence of a dark spot on the more massive component.The extremely high fill-out factor suggests that the merging of the contact binary is driven by dynamical mass loss from the outer Lagrange point.However,the analysis of the 2004 light curve indicates that no solutions were obtained even at an extremely low mass ratio of q=0.03.This suggests that the common convective envelope of the binary system disappeared and the secondary component spiraled into the envelope of the primary in 2004.Finally,the ejection of the envelope of the primary produced the outburst.
基金Supported by the National Natural Science Foundation of Chinasupported by the Natural Science Foundation of China (Grant No. 11133001)+1 种基金the National Basic Research Program of China (973 Program, 2009CB824800)the Qinglan project of Jiangsu Province
文摘We perform numerical calculations to simulate the evolution of low-mass X-ray binary systems. For the accreting compact object we consider the initial mass of 1.4, 10, 20, 100, 200, 500 and 1000 Mo, corresponding to neutron stars （NSs）, stellar- mass black holes （BHs） and intermediate-mass BHs. Mass transfer in these binaries is driven by nuclear evolution of the donors and/or orbital angular momentum loss due to magnetic braking and gravitational wave radiation. For the different systems, we determine their bifurcation periods Pbif that separate the formation of converging systems from the diverging ones, and show that Pbif changes from ~ 1 d to ≥ 3 d for a 1 Mo donor star, with increasing initial accretor mass from 1.4 to 1000 Mo. This means that the dominant mechanism of orbital angular momentum loss changes from magnetic braking to gravitational radiation. As an illustration we compare the evolution of binaries consisting of a secondary star of 1 Mo at a fixed initial period of 2 d. In the case of the NS or stellar-mass BH accretor, the system evolves to a well-detached He white dwarf-neutron star/black hole pair, but it evolves to an ultra- compact binary if the compact object is an intermediate-mass BH. Thus the binary evolution heavily depends upon the mass of the compact object. However, we show that the final orbital period-white dwarf mass relation found for NS low-mass X-ray binaries is fairly insensitive to the initial mass of the accreting star, even if it is an intermediate-mass BH.
文摘We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the helium-rich matter in the center of the primary is mixed into the envelope, and there is little distinction in the evolutionary tracks of the mergers. The timescales of the mergers remaining on the main sequence, tBS are very similar (-6.2×108yr) if qmix< 0.71, since no hydrogen-rich matter of the secondary is mixed into the core of the mergers; for qmix > 0.71, the larger qmix is, the greater the mixing, hence the longer the blue straggler lifetime, tBS, and also the greater the luminosity. For qmix= 1.00, tBS -8.5×108yr. Estimation by (?)r - (?)a = 0.0 shows that the point at which tBS begins to increase is about qmix= 0.68. In comparison with the homogeneously mixed models, the merger with a helium profile similar to that of the primary is less luminous and has a shorter tBS.
基金supported by the National Basic Research Program of China(973 program,2014CB845700)the National Natural Science Foundation of China(Grant Nos.11322327,11390371,11473063,11033008 and 61561053)+2 种基金the Foundation of State Ethnic Affairs Commission(Grant No.12YNZ008)the Science Foundation of Key Laboratory in Software Engineering(Grant No.2012SE402)the Natural Science Foundation of Yunnan Province(Grant Nos.2013FB083 and 2013HB097)
文摘The core-degenerate （CD） scenario has been suggested to be a possible progenitor model of type Ia supernovae （SNe Ia）, in which a carbon-oxygen white dwarf merges with the hot CO core of a massive asymptotic giant branch star dur- ing their common-envelope phase. However, the SN Ia birthrates for this scenario are still uncertain. We conducted a detailed investigation into the CD scenario and then gave the birthrates for this scenario using a detailed Monte Carlo binary pop- ulation synthesis approach. We found that the delay times of SNe Ia from this sce- nario are -70 Myr- 1400 Myr, which means that the CD scenario contributes to young SN Ia populations. The Galactic SN Ia birthrates for this scenario are in the range of ~7.4×10^-5 yr^-1- 3.7 × 10^-4 yr^-1, which roughly accounts for -2%-10% of all SNe Ia. This indicates that, under the assumptions made here, the CD scenario only contributes a small portion of all SNe Ia, which is not consistent with the results of Ilkov ＆ Soker.
基金funded by the National Natural Science Foundation of China(Grant Nos.11133001 and 11333004)the Strategic Priority Research Program of CAS(Grant No.XDB09000000)
文摘Abstract The binding energy parameter A plays a vital role in common envelope evolution. Though it is well known that A takes different values for stars with different masses and varies during stellar evolution, it has been erroneously adopted as a constant in most population synthesis calculations. We have system- atically calculated the values of A for stars of masses 1 - 60 M by use of an updated stellar evolution code, taking into account the contribution from both gravitational energy and internal energy to the binding energy of the envelope. We adopt the criterion for the core-envelope boundary advocated by Ivanova. A new kind of A with an enthalpy prescription is also investigated. We present fitting formulae for the calculated values of various kinds of A, which can be used in future population synthesis studies.
基金supported by the National Basic Research Program of China (973 program,2014CB845700)the Chinese Academy of Sciences (Nos.KJZD-EW-M06-01 and QYZDBSSW-SYS001)+1 种基金the National Natural Science Foundation of China (Nos.11673059,11521303,11390374 and 11573016)the Natural Science Foundation of Yunnan Province (Nos.2013HB097,2013HA005 and 2017HC018)
文摘The final outcomes of accreting ONe white dwarfs（ONe WDs） have been studied for several decades,but there are still some issues that are not resolved. Recently,some studies suggested that the deflagration of oxygen would occur for accreting ONe WDs with Chandrasekhar masses. In this paper,we aim to investigate whether ONe WDs can experience accretion-induced collapse（AIC） or explosions when their masses approach the Chandrasekhar limit. Employing the stellar evolution code Modules for Experiments in Stellar Astrophysics（MESA）,we simulate the longterm evolution of ONe WDs with accreting CO material. The ONe WDs undergo weak multicycle carbon flashes during the mass-accretion process,leading to mass increase of the WDs. We found that different initial WD masses and mass-accretion rates influence the evolution of central density and temperature. However,the central temperature cannot reach the explosive oxygen ignition temperature due to neutrino cooling. This work implies that the final outcome of accreting ONe WDs is electroncapture induced collapse rather than thermonuclear explosion.
基金supported by NSFC (11522327, 11473036, 11521303 and 11390374)CAS “Light of West China” Program, CAS (No. KJZD-EW-M06-01)the Science and Technology Innovation Talent Program of Yunnan Province (Grant No. 2013HA005)
文摘The single-degenerate(SD)model is one of the most popular progenitor models of type Ia supernovae(SNe Ia),in which the companion star can survive after an SN Ia explosion and show peculiar properties.Therefore,searching for the surviving companion in type Ia supernova remnants(SNRs)is a potential method to verify the SD model.In the SN 1604 remnant(Kepler’s SNR),although Chandra X-ray observation suggests that the progenitor is most likely a WD+AGB system,the surviving companion has not been found.One possible reason is rapid rotation of the white dwarf(WD),causing explosion of the WD to be delayed for a spin-down timescale,and then the companion evolved into a WD before the supernova explosion,so the companion is too dim to be detected.We aim to verify this possible explanation by carrying out binary evolution calculations.In this paper,we use Eggleton’s stellar evolution code to calculate the evolution of binaries consisting of a WD+red giant(RG).We assume that the rapidly rotating WD can continuously increase its mass when its mass exceeds the Chandrasekhar mass limit(MCh=1.378 M_⊙)until the mass-transfer rate decreases to be lower than a critical value.Eventually,we obtain the final masses of a WD in the range 1.378 M_⊙ to 2.707 M_⊙.We also show that if the spin-down time is less than 10~6yr,the companion star will be very bright and easily observed;but if the spin-down time is as long as^10~7 yr,the luminosities of the surviving companion would be lower than the detection limit.Our simulation provides guidance in hunting for the surviving companion stars in SNRs,and the fact that no surviving companion has been found in Kepler’s SNR may not be definite evidence disfavoring the SD origin of Kepler’s SN.
文摘New three color light curves of TY Boo were acquired during five nights from February to May 2006 in the BVR bandpass using a 50-cm F/8.4 Ritchey- Chr6tien telescope （Ba50） at the Baja Astronomical Observatory （Hungary）, with a 512×512 Apogee AP-7 CCD camera. A photometric solution of these light curves was obtained by means of the Wilson-Devinney code. The results showed that the less massive component is hotter than the more massive one, and the temperature difference between the components is △T -249 K. Long term investigation of the system based on all available data shows two stages of increase and a similar trend for decrease, which appears to be periodic behavior. A set of new light elements yields a new period （P = 0.3171506d） and shows a periodic decrease with the rate dP/dE -- 5.858×10^-12 d cycle-1, 6.742×10^-9 d yr-1 or 0.058 s century-1. The evolutionary status of the system is discussed.
基金supported by the National Basic Research Program of China(973 program,2014CB845700)the National Natural Science Foundation of China(Nos.11322327,11390374,11521303 and 61561053)+2 种基金the Chinese Academy of Sciences(Nos.KJZD-EW-M06-01 and XDB09010202)the Natural Science Foundation of Yunnan Province(Nos.2013HB097 and 2013FB083)the Youth Innovation Promotion Association,CAS
文摘Type Ia supernovae （SNe Ia） play an important role in studies of cosmology and galactic chemi- cal evolution. They are believed to be thermonuclear explosions of carbon-oxygen white dwarfs （CO WDs） when their masses approach the Chandrasekar （Ch） mass limit. However, it is still not completely under- stood how a CO WD increases its mass to the Ch-mass limit in the classical single-degenerate （SD） model. In this paper, we studied the mass accretion process in the SD model to examine whether the WD can explode as an SN Ia. Employing the stellar evolution code called modules for experiments in stellar as- trophysics （MESA）, we simulated the He accretion process onto CO WDs. We found that the WD can increase its mass to the Ch-mass limit through the SD model and explosive carbon ignition finally occurs in its center, which will lead to an SN Ia explosion. Our results imply that SNe Ia can be produced from the SD model through steady helium accretion. Moreover, this work can provide initial input parameters for explosion models of SNe Ia.
基金supported by the Scientific and Technological Research Council of Turkey(TBTAK 112T989)
文摘Grids of stellar evolution omy/astrophysics, such as planet hosting are required in many fields of astron- stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models with updated ingredients and recently determined solar abundances is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough （0.01 M） that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00M. We present results in different forms of tables for easy and general appli- cation. The second stellar harmonic, required for analysis of apsidal motion of eclips- ing binaries, is also listed. We also construct rotating models to determine the effect of rotation on stellar structure and derive fitting formulae for luminosity, radius and the second harmonic as a function of rotational parameter. We also compute and list colors and bolometric corrections of models required for transformation between theo- retical and observational results. The results are tested for the Sun, the Hyades cluster, the slowly rotating chemically peculiar Am stars and eclipsing binaries with apsidal motion. The theoretical and observational results along isochrones are in good agree- ment. The grids are also applicable to rotating stars provided that equatorial velocity is given.
基金Supported by the National Natural Science Foundation of China
文摘Although Type Ia supernovae （SNe Ia） play an important role in the study of cosmology, their progenitors are still poorly understood. Thermonuclear explosions from the helium double-detonation sub-Chandrasekhar mass model have been considered as an alternative method for producing SNe Ia. By adopting the assumption that a double detonation occurs when a He layer with a critical ignition mass accumulates on the surface of a carbon-oxygen white dwarf （CO WD）, we perform detailed binary evolution calculations for the He double-detonation model, in which a He layer from a He star accumulates on a CO WD. According to these calculations, we obtain the initial parameter spaces for SNe Ia in the orbital period and secondary mass plane for various initial WD masses. We implement these results into a detailed binary population synthesis approach to calculate SN Ia birthrates and delay times. From this model, the SN Ia birthrate in our Galaxy is ～0.4 - 1.6 × 10^-3 yr^-1. This indicates that the double-detonation model only produces part of the SNe la. The delay times from this model are ～ 70 - 710 Myr, which contribute to the young population of SNe Ia in the observations. We found that the CO WD ＋ sdB star system CD-30 11223 could produce an SN Ia via the double-detonation model in its future evolution.
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.
基金supported by the National Natural Science Foundation of China (Grant Nos.10763001,10963003 and 11063002)the Natural Science Foundation of Xinjiang (Nos.2009211B01 and 2010211B05)+1 种基金the Foundation of Huoyingdong(No.121107)the Scientific Research Program of the Higher Education Institutions of Xinjiang(No.XJEDU2008S12)
文摘By simulating the evolution of spin periods of magnetized neutron stars which interact with their environment in binary systems,we investigate the Galactic population of high mass X-ray binaries（HMXBs） .The number of HMXBs in the Galaxy is between 190 and 240,and their birthrate is from 5.9×10-5 yr-1 to 6.3× 10-5 yr-1.Comparing the Corbet diagram（the positions of the spin periods vs.the orbital periods of HMXBs） in our model with the associated observations,we find that the stellar wind structure and the process of matter transfer are very important for understanding HMXBs.
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 the study of cosmic evolution, especially in cosmology. There are several progenitor models for SNe Ia proposed in the past years. By considering the effect of accretion disk instability on the evolution of white dwarf （WD） binaries, we performed detailed binary evolution calculations for the WD ＋ red-giant （RG） channel of SNe Ia, in which a carbon--oxygen WD accretes material from a RG star to increase its mass to the Chandrasekhar mass limit. According to these calculations, we mapped out the initial and final parameters for SNe Ia in the orbital period-secondary mass （log Pi_ M2^i） plane for various WD masses for this channel. We discussed the influence of the variation of the duty cycle value on the regions for producing SNe Ia. Similar to previous studies, this work also indicates that the long-period dwarf novae offer possible ways for producing SNe Ia. Meanwhile, we find that the surviving companion stars from this channel have a low mass after the SN explosion, which may provide a means for the formation of the population of single low-mass WDs （〈0.45 M⊙）.
基金Supported by the National Natural Science Foundation of China.
文摘Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow （RLOF）. The RLOF can be divided into two cases： dynamically unstable and stable. In the first case, the birthrate of symbiotic stars is 0.056 yr^- 1 or 0.045 yr^-1 depending on different assumptions; in the stable RLOF case, it is 0.002 yr^-1 or 0.005yr^-1. The number of symbiotic stars with main-sequence accretors and unstable RLOF in our galaxy is about 5, that with stable RLOF is about 60 to 280. Comparison between our results with those of Yungelson et al. shows that symbiotic stars with MS accretors make only a small contribution （ ≤ 8%） to the whole population of symbiotic stars in the Galaxy.
