In this paper, we investigate the problem of supersonic convection caused by the application of the usual Mixing Length Theory (MLT), and give a modification to the original expression of the MLT. In the case of the u...In this paper, we investigate the problem of supersonic convection caused by the application of the usual Mixing Length Theory (MLT), and give a modification to the original expression of the MLT. In the case of the usual MLT, a zone of supersonic convection exists when the stellar model goes into yellow-red supergiant phase. When the modification is applied, the models of late type supergiants possess shallower convective envelopes for a given temperature compared with the normal formalism of the MLT. Therefore the stellar models made with our new formalism move to lower effective temperature by 100-400 K depending on the luminosity of the star. Such a modification does not affect the convective envelope structure of lower luminosity late type stars, as both expressions of the MLT give the same result. In these stars.展开更多
We have investigated the relation between the orbital period P<SUB>orb</SUB> and the spin period P<SUB>s</SUB> of neutron stars in OB/X-ray binaries. By simulating the time-development of the m...We have investigated the relation between the orbital period P<SUB>orb</SUB> and the spin period P<SUB>s</SUB> of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M<SUB>☉</SUB> donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B<SUB>0</SUB> stronger than about 3×10<SUP>12</SUP> G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B<SUB>0</SUB> < 3×10<SUP>12</SUP> G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the P<SUB>s</SUB>-P<SUB>orb</SUB> diagram.展开更多
In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars （NSs） could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based ...In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars （NSs） could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based on a consideration of the coupling of the r-modes and the stellar spin and thermal evolution, we carefully investigate the influences of the differential rotation on the long-term evolution of isolated NSs and NSs in low-mass X-ray binaries, where the viscous damping of the r-modes and its resultant effects are taken into account. The numerical results show that, for both kinds of NSs, the differential rotation can significantly prolong the duration of the r-modes. As a result, the stars can keep nearly a constant temperature and constant angular velocity for over a thousand years. Moreover, the persistent radiation of a quasi-monochromatic gravitational wave would also be predicted due to the long-term steady r-mode oscillation and stellar rotation. This increases the detectability of gravitational waves from both young isolated and old accreting NSs.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
In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between ...In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between which are the radiative inter- mediate layers with uneven chemical abundances. Semiconvection would occur in the intermediate layers between the convective core and the homogeneous envelope in massive stars. We treat core convective overshooting and semiconvection together as a process. We found that when decreasing overshooting, the semiconvection is more pronounced. In these two processes, we introduce one diffusive parameter D, which is different from other authors who have introduced different parameters for these two zones. The influences of the turbulent diffusion process on chemical evolution and other quantities of the stellar structure are shown in the present paper.展开更多
Recent studies have increasingly identified extended main sequence turn-off(e MSTO)phenomena in Galactic open clusters,yet the number of such clusters with sufficient spectroscopic information for member stars remains...Recent studies have increasingly identified extended main sequence turn-off(e MSTO)phenomena in Galactic open clusters,yet the number of such clusters with sufficient spectroscopic information for member stars remains limited.Unlike most studies that rely on fitting isochrones based on color–magnitude diagram(CMD)morphology to account for varying rotational velocities,our approach leverages LAMOST spectral data to compute actual rotational velocity distributions for confirmed cluster members,along with parameters such as metallicity,differential extinction,and rotational inclination,to utilize PARSEC isochrones for fitting the cluster CMDs.We systematically surveyed all known Galactic open clusters and selected 12 clusters where rotational velocity distributions could be reliably calculated for detailed fitting.Our results successfully reproduced the eMSTO phenomenon observed in these clusters.For the majority of clusters,considering only differential extinction and variations in rotational velocity adequately explains the position and morphology of the MSTO.For some intermediate-age clusters,incorporating rotational inclination additionally accounts for the broadening of the MSTO.This study underscores the importance of spectroscopic data in understanding eMSTO phenomena and provides a probable explanation for interpreting the combined effects of differential extinction,rotation,and inclination on the CMDs of Galactic open clusters.展开更多
In the current paper,we present a study of the spatial distribution of luminous blue variables(LBVs)and various LBV candidates(c LBVs)with respect to OB associations in the galaxy M33.The identification of blue star g...In the current paper,we present a study of the spatial distribution of luminous blue variables(LBVs)and various LBV candidates(c LBVs)with respect to OB associations in the galaxy M33.The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields.We have found that the distribution of distances to the nearest OB association obtained for the LBV/c LBV sample is close to that for massive stars with Minit>20 M⊙and WolfRayet stars.This result is in good agreement with the standard assumption that LBVs represent an intermediate stage in the evolution of the most massive stars.However,some objects from the LBV/cLBV sample,particularly Fe II-emission stars,demonstrated severe isolation compared to other massive stars,which,together with certain features of their spectra,implicitly indicates that the nature of these objects and other LBVs/cLBVs may differ radically.展开更多
Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope.Most of them are main-sequence stars,but some of them are post main-...Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope.Most of them are main-sequence stars,but some of them are post main-sequence systems.They are good astrophysical laboratories for studying several problems such as the merging of binary stars,evolution of the common envelope,the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems.A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic survey.Based on follow-up observations,the evolutionary states and geometrical structures of some systems were understood well.In this review,we will introduce and catalog new stellar atmospheric parameters(i.e.,the effective temperature(Teff),the gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(Vr))for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of LAMOST.Then we will focus on several groups of contact binary stars,i.e.,marginal contact binary systems,deep and low-mass ratio contact binary stars,binary systems below the short-period limit of contact binaries and evolved contact binaries.Marginal contact binaries are at the beginning of the contact stage,while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked binaries.Several statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are reviewed.The period-color relation of M-type binaries reveals that there are contact binaries below the short-period limit.Searching for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period limit is about 0.15 d.Some evolved contact binaries were detected by the LAMOST survey where both components are sub-giants or giants.They provide a good opportunity to investigate evolution of the common envelope and are the progenitors of luminous red novae like V1309 Sco.展开更多
Based on previous works of OPAL, we construct a series of opacity tables for various metaUicities Z = 0, 0.00001, 0,00003, 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables c...Based on previous works of OPAL, we construct a series of opacity tables for various metaUicities Z = 0, 0.00001, 0,00003, 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton＇s stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10 （T/K） 〉 3.95 and Alexander＇s for log10 （T/K） 〈 3.95. At log10 （T/K） = 3.95, the two groups＇ data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M⊙ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.展开更多
Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected ...Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO star sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars by combining asteroseismic parameters deduced from Kepler photometry and atmospheric parameters deduced from LAMOST spectra. With this sample, we examine the age determination as well as the contamination rate of the MSTO star sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr （7%） and a dispersion of 2.71 Gyr （28%）. The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.展开更多
BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are ana...BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A3 = 0.024 d and a period of P3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M2 = 2.8×10^-6 M⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M⊙ at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.展开更多
Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar...Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar neutrino luminosity with different masses.The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated.We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61×10^9 yr is consistent with that of the Sun.In general,neutrinos are produced by nuclear reactions,and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity.However,neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙.Although the helium flash does not produce neutrinos,plasma decay,one of the thermal processes,can efficiently make neutrinos during this stage.Due to the high mass-loss rate,a star with a mass of 9 M⊙ does not undergo the helium flash.Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage.At the end of the AGB stage,its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.展开更多
The accretion-induced collapse(AIC)scenario was proposed 40 years ago as an evolutionary end state of oxygen-neon white dwarfs(ONe WDs),linking them to the formation of neutron star(NS)systems.However,there has been n...The accretion-induced collapse(AIC)scenario was proposed 40 years ago as an evolutionary end state of oxygen-neon white dwarfs(ONe WDs),linking them to the formation of neutron star(NS)systems.However,there has been no direct detection of any AIC event so far,even though there exists a lot of indirect observational evidence.Meanwhile,the evolutionary pathways resulting in NS formation through AIC are still not thoroughly investigated.In this article,we review recent studies on the two classic progenitor models of AIC events,i.e.,the single-degenerate model(including the ONe WD+MS/RG/He star channels and the CO WD+He star channel)and the double-degenerate model(including the double CO WD channel,the double ONe WD channel and the ONe WD+CO WD channel).Recent progress on these progenitor models is reviewed,including the evolutionary scenarios leading to AIC events,the initial parameter space for producing AIC events and the related objects(e.g.,the pre-AIC systems and the post-AIC systems).For the single-degenerate model,the pre-AIC systems(i.e.,the progenitor systems of AIC events)could potentially be identified as supersoft X-ray sources,symbiotics and cataclysmic variables(such as classical novae,recurrent novae,Ne novae and He novae)in the observations,whereas the post-AIC systems(i.e.,NS systems)could potentially be identified as low-/intermediate-mass X-ray binaries,and the resulting low-/intermediate-mass binary pulsars,most notably millisecond pulsars.For the double-degenerate model,the pre-AIC systems are close double WDs with short orbital periods,whereas the post-AIC systems are single isolated NSs that may correspond to a specific kind of NS with peculiar properties.We also review the predicted rates of AIC events,the mass distribution of NSs produced via AIC and the gravitational wave(GW)signals from double WDs that are potential GW sources in the Galaxy in the context of future spacebased GW detectors,such as LISA,TianQin,Taiji,etc.Recent theoretical and observational constraints on the detection of AIC events are summarized.In order to confirm the existence of the AIC process,and resolve this long-term issue presented by current stellar evolution theories,more numerical simulations and observational identifications are required.展开更多
To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) t...To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) telescope.Based on the observations of APEX,we obtain luminosity to mass ratios Lclump/Mclump that range from 10 to 154 L_(⊙)/M_(⊙),where some of them embedded ultra compact(UC) H Ⅱ region.Using the SMA,CH3CN(12K-11K) transitions were observed toward nine massive starforming regions.We derive the CH3CN rotational temperature and column density using the XCLASS program,and calculate its fractional abundance.We find that CH3CN temperature seems to increase with the increase of Lclump/Mclump when the ratio is between 10 to 40 L_(⊙)/M_(⊙),then decrease when L_(clump)/M_(clump)≥ 40 L_(⊙)/M_(⊙).Assuming that the CH3CN gas is heated by radiation from the central star,the effective distance of CH3CN relative to the central star is estimated.The distance ranges from - 0.003 to - 0.083 pc,which accounts for - 1/100 to - 1/1000 of clump size.The effective distance increases slightly as Lclump/Mclump increases(Reff-(L_(clump)/M_(clump))0.5±0.2).Overall,the CH3 CN abundance is found to decrease as the clumps evolve,e.g.,XCH3CN -(L_(clump)/M_(clump))-1.0±0.7.The steady decline of CH3CN abundance as the clumps evolution can be interpreted as a result of photodissociation.展开更多
We investigate the rotation profile of solar-like stars with magnetic fields. A diffu- sion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the ...We investigate the rotation profile of solar-like stars with magnetic fields. A diffu- sion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the coefficient are computed to give the rotation profiles. The total angular momentum of a solar model with only hydrodynamic instabilities is about 13 times larger than that of the Sun at the age of the Sun, and this model can not reproduce quasi-solid rotation in the radiative region. However, the solar model with magnetic fields not only can reproduce an almost uniform rotation in the radiative region, but also a total angular momentum that is consistent with the helioseismic result at the 3 tr level at the age of the Sun. The rotation of solar-like stars with magnetic fields is almost uniform in the radiative region, but for models of 1.2-1.5 MG, there is an obvious transition region between the convective core and the radiative region, where angular velocity has a sharp radial gradient, which is different from the rotation profile of the Sun and of massive stars with magnetic fields. The change of angular velocity in the transition region increases with increasing age and mass.展开更多
In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported.The star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 ...In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported.The star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia.V1180 Cas shows large amplitude variability,interpreted as a combination of accretion-induced and extinction-driven effects.Our data from VRI CCD photometric observations of the star were collected from September 2011 to February 2022.During our monitoring,we recorded several brightness dips with large amplitudes of up to 5 mag(I band).At the same time,increases in brightness over periods of several weeks have also been recorded.In this paper,we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.展开更多
PSR J1946+3417 is a millisecond pulsar(MSP)with a spin period P?3.17 ms.Harbored in a binary with an orbital period Pb?27 days,the MSP is accompanied by a white dwarf(WD).The masses of the MSP and the WD were determin...PSR J1946+3417 is a millisecond pulsar(MSP)with a spin period P?3.17 ms.Harbored in a binary with an orbital period Pb?27 days,the MSP is accompanied by a white dwarf(WD).The masses of the MSP and the WD were determined to be 1.83 M⊙,and 0.266 M⊙,respectively.Specially,its orbital eccentricity is e?0.134,which is challenging the recycling model of MSPs.Assuming that the neutron star in a binary may collapse to a strange star when its mass reaches a critical limit,we propose a phase transition(PT)scenario to account for the origin of the system.The sudden mass loss and the kick induced by asymmetric collapse during the PT may result in the orbital eccentricity.If the PT event takes place after the mass transfer ceases,the eccentric orbit cannot be re-circularized in the Hubble time.Aiming at the masses of both components,we simulate the evolution of the progenitor of PSR J1946+3417 via MESA.The simulations show that an NS/main sequence star binary with initial masses of 1.4+1.6 M⊙in an initial orbit of 2.59 days will evolve into a binary consisting of a 2.0 M⊙MSP and a 0.27 M⊙WD in an orbit of~21.5 days.Assuming that the gravitational mass loss fraction during PT is 10%,we simulate the effect of PT via the kick program of BSE with a velocity ofσPT=60 km s-1.The results show that the PT scenario can reproduce the observed orbital period and eccentricity with higher probability than other values.展开更多
In this work,the pulsation analysis is performed on 83 high-amplitudeδScuti stars(HADS),which have been observed by the Transiting Exoplanet Survey Satellite.The results show that 49 of these HADS show single-mode pu...In this work,the pulsation analysis is performed on 83 high-amplitudeδScuti stars(HADS),which have been observed by the Transiting Exoplanet Survey Satellite.The results show that 49 of these HADS show single-mode pulsation,27 of them show radial double-modes pulsation(in which 22 of them pulsate with the fundamental and first overtone modes and five of them pulsate with the first and second overtone modes),and seven of them show radial triple-modes pulsation(three of which are newly confirmed triple-mode HADS).The histogram of the fundamental periods and the ratios between the fundamental and first overtone periods show bimodal structures,which might be caused by the stellar evolution in this specific phase.Most of the radial triple-mode HADS have a fundamental amplitude of 41-54 mmag,and 50%of them have similar amplitudes of the fundamental and first overtone pulsation modes.All these hints require further confirmation not only in observations with more HADS samples,but also in theoretical models with suitable treatments of stellar evolution and pulsation.展开更多
Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is an A-subtype contact binary with low mass ratio(q = 0.178) while NW Leo has ...Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is an A-subtype contact binary with low mass ratio(q = 0.178) while NW Leo has a high mass ratio(q = 0.707). For CSS J075415.6+191052, the RI light curves show weakening around the left shoulder of the secondary minimum, which indicates that there may be a dark spot on the secondary component. However, the light curves of BV bands are totally symmetric. It is unreasonable if the dark spot is caused by magnetic activity or mass transfer between the two components. Therefore, weakening of the light curves in this contact binary is caused by something else. A possible explanation is mass transferring from the primary component to the common convective envelope through the inner Lagrangian point, and this part of the mass, for some reason, weakens the RI bands of light from the secondary component. O-C analysis of NW Leo reveals a cyclic period change with a modulation period of 4.7 yr, which may be caused by the light travel time effect of a third body. The positions of CSS J075415.6+191052 and NW Leo in the P–J′_(orb)diagram indicate that CSS J075415.6+191052 mainly abides by the angular momentum loss theory while NW Leo is dominated by the thermal relaxation oscillation theory.展开更多
Using Eggleton＇s code, we systematically show the differences in stellar evolution between the results based on the scaled-solar mixture and the a-enhanced metal mixture. As input, the OPAL high temperature opacities...Using Eggleton＇s code, we systematically show the differences in stellar evolution between the results based on the scaled-solar mixture and the a-enhanced metal mixture. As input, the OPAL high temperature opacities are used for log（T/K） 〉 4.00, and the new Wichita State low temperature opacities, for log（T/K） ≤ 4.00, Our calculations cover star masses ranging from 0.25 to 80.0M⊙, spaced at ΔlogM = 0.10 or 0.05. The values of metallicities Z are 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08 and 0.10. For a given Z, the initial hydrogen mass fraction is given by X = 0.76 - 3.0Z. We show that a-enhancement can raise the stellar effective temperature and luminosity, and reduce the evolutionary age. Compared with some previous work, the effects of α-enhancement are more obviously demonstrated in our calculations.展开更多
基金the NationalNatural Science Foundation of China (NSFC) this work is also partly supported by the Ministryof Science and Tec
文摘In this paper, we investigate the problem of supersonic convection caused by the application of the usual Mixing Length Theory (MLT), and give a modification to the original expression of the MLT. In the case of the usual MLT, a zone of supersonic convection exists when the stellar model goes into yellow-red supergiant phase. When the modification is applied, the models of late type supergiants possess shallower convective envelopes for a given temperature compared with the normal formalism of the MLT. Therefore the stellar models made with our new formalism move to lower effective temperature by 100-400 K depending on the luminosity of the star. Such a modification does not affect the convective envelope structure of lower luminosity late type stars, as both expressions of the MLT give the same result. In these stars.
基金Supported by the National Natural Science Foundation of China.
文摘We have investigated the relation between the orbital period P<SUB>orb</SUB> and the spin period P<SUB>s</SUB> of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M<SUB>☉</SUB> donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B<SUB>0</SUB> stronger than about 3×10<SUP>12</SUP> G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B<SUB>0</SUB> < 3×10<SUP>12</SUP> G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the P<SUB>s</SUB>-P<SUB>orb</SUB> diagram.
基金Supported by the National Natural Science Foundation of China(Grant Nos.10603002 and 10773004)
文摘In a second-order r-mode theory, Sa and Tome found that the r-mode oscillation in neutron stars （NSs） could induce stellar differential rotation, which naturally leads to a saturated state of the oscillation. Based on a consideration of the coupling of the r-modes and the stellar spin and thermal evolution, we carefully investigate the influences of the differential rotation on the long-term evolution of isolated NSs and NSs in low-mass X-ray binaries, where the viscous damping of the r-modes and its resultant effects are taken into account. The numerical results show that, for both kinds of NSs, the differential rotation can significantly prolong the duration of the r-modes. As a result, the stars can keep nearly a constant temperature and constant angular velocity for over a thousand years. Moreover, the persistent radiation of a quasi-monochromatic gravitational wave would also be predicted due to the long-term steady r-mode oscillation and stellar rotation. This increases the detectability of gravitational waves from both young isolated and old accreting NSs.
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co-sponsored by the National Natural Science Foundation of China (Grant Nos.11333006 and 10973035)the Chinese Academy of Sciences (Grant No.KJCX2-YW-T24)
文摘In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between which are the radiative inter- mediate layers with uneven chemical abundances. Semiconvection would occur in the intermediate layers between the convective core and the homogeneous envelope in massive stars. We treat core convective overshooting and semiconvection together as a process. We found that when decreasing overshooting, the semiconvection is more pronounced. In these two processes, we introduce one diffusive parameter D, which is different from other authors who have introduced different parameters for these two zones. The influences of the turbulent diffusion process on chemical evolution and other quantities of the stellar structure are shown in the present paper.
基金supported by the National Natural Science Foundation of China,No.12261141689。
文摘Recent studies have increasingly identified extended main sequence turn-off(e MSTO)phenomena in Galactic open clusters,yet the number of such clusters with sufficient spectroscopic information for member stars remains limited.Unlike most studies that rely on fitting isochrones based on color–magnitude diagram(CMD)morphology to account for varying rotational velocities,our approach leverages LAMOST spectral data to compute actual rotational velocity distributions for confirmed cluster members,along with parameters such as metallicity,differential extinction,and rotational inclination,to utilize PARSEC isochrones for fitting the cluster CMDs.We systematically surveyed all known Galactic open clusters and selected 12 clusters where rotational velocity distributions could be reliably calculated for detailed fitting.Our results successfully reproduced the eMSTO phenomenon observed in these clusters.For the majority of clusters,considering only differential extinction and variations in rotational velocity adequately explains the position and morphology of the MSTO.For some intermediate-age clusters,incorporating rotational inclination additionally accounts for the broadening of the MSTO.This study underscores the importance of spectroscopic data in understanding eMSTO phenomena and provides a probable explanation for interpreting the combined effects of differential extinction,rotation,and inclination on the CMDs of Galactic open clusters.
文摘In the current paper,we present a study of the spatial distribution of luminous blue variables(LBVs)and various LBV candidates(c LBVs)with respect to OB associations in the galaxy M33.The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields.We have found that the distribution of distances to the nearest OB association obtained for the LBV/c LBV sample is close to that for massive stars with Minit>20 M⊙and WolfRayet stars.This result is in good agreement with the standard assumption that LBVs represent an intermediate stage in the evolution of the most massive stars.However,some objects from the LBV/cLBV sample,particularly Fe II-emission stars,demonstrated severe isolation compared to other massive stars,which,together with certain features of their spectra,implicitly indicates that the nature of these objects and other LBVs/cLBVs may differ radically.
基金supported by the National Natural Science Foundation of China(Nos.11933008,11922306,11773066 and 11903076)the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences。
文摘Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope.Most of them are main-sequence stars,but some of them are post main-sequence systems.They are good astrophysical laboratories for studying several problems such as the merging of binary stars,evolution of the common envelope,the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems.A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic survey.Based on follow-up observations,the evolutionary states and geometrical structures of some systems were understood well.In this review,we will introduce and catalog new stellar atmospheric parameters(i.e.,the effective temperature(Teff),the gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(Vr))for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of LAMOST.Then we will focus on several groups of contact binary stars,i.e.,marginal contact binary systems,deep and low-mass ratio contact binary stars,binary systems below the short-period limit of contact binaries and evolved contact binaries.Marginal contact binaries are at the beginning of the contact stage,while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked binaries.Several statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are reviewed.The period-color relation of M-type binaries reveals that there are contact binaries below the short-period limit.Searching for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period limit is about 0.15 d.Some evolved contact binaries were detected by the LAMOST survey where both components are sub-giants or giants.They provide a good opportunity to investigate evolution of the common envelope and are the progenitors of luminous red novae like V1309 Sco.
基金Supported by the National Natural Science Foundation of China.
文摘Based on previous works of OPAL, we construct a series of opacity tables for various metaUicities Z = 0, 0.00001, 0,00003, 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton＇s stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10 （T/K） 〉 3.95 and Alexander＇s for log10 （T/K） 〈 3.95. At log10 （T/K） = 3.95, the two groups＇ data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M⊙ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.
基金The Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission+4 种基金National Astronomical Observatories, Chinese Academy of Sciencessupported by grants 11273007 and 10933002 from the National Natural Science Foundation of Chinathe Joint Research Fund in Astronomy (U1631236) under cooperative agreement between the National Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS)the Fundamental Research Funds for the Central UniversitiesYouth Scholars Program of Beijing Normal University
文摘Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO star sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars by combining asteroseismic parameters deduced from Kepler photometry and atmospheric parameters deduced from LAMOST spectra. With this sample, we examine the age determination as well as the contamination rate of the MSTO star sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr （7%） and a dispersion of 2.71 Gyr （28%）. The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.
基金supported by the National Natural Science Foundation of China(Grant No.11325315)
文摘BH Cen is a short-period early-type binary with a period of 0.792^d in the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A3 = 0.024 d and a period of P3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M2 = 2.8×10^-6 M⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M⊙ at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.
基金support of the National Natural Science Foundation of China(Grant Nos.11763007,11473024,11463005,11863005,11803026 and 11503008)the Tianshan Youth Project of Xinjiang(2017Q014)
文摘Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar neutrino luminosity with different masses.The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated.We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61×10^9 yr is consistent with that of the Sun.In general,neutrinos are produced by nuclear reactions,and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity.However,neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙.Although the helium flash does not produce neutrinos,plasma decay,one of the thermal processes,can efficiently make neutrinos during this stage.Due to the high mass-loss rate,a star with a mass of 9 M⊙ does not undergo the helium flash.Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage.At the end of the AGB stage,its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.
基金the National Natural Science Foundation of China(Grant Nos.11521303,11673059 and 11873085)the Chinese Academy of Sciences(No.QYZDB-SSW-SYS001)+2 种基金Yunnan Province(Nos.2018FB005 and 2019FJ001)supported by the National Natural Science Foundation of China(Grant No.11903075)the Western Light Youth Project of Chinese Academy of Sciences。
文摘The accretion-induced collapse(AIC)scenario was proposed 40 years ago as an evolutionary end state of oxygen-neon white dwarfs(ONe WDs),linking them to the formation of neutron star(NS)systems.However,there has been no direct detection of any AIC event so far,even though there exists a lot of indirect observational evidence.Meanwhile,the evolutionary pathways resulting in NS formation through AIC are still not thoroughly investigated.In this article,we review recent studies on the two classic progenitor models of AIC events,i.e.,the single-degenerate model(including the ONe WD+MS/RG/He star channels and the CO WD+He star channel)and the double-degenerate model(including the double CO WD channel,the double ONe WD channel and the ONe WD+CO WD channel).Recent progress on these progenitor models is reviewed,including the evolutionary scenarios leading to AIC events,the initial parameter space for producing AIC events and the related objects(e.g.,the pre-AIC systems and the post-AIC systems).For the single-degenerate model,the pre-AIC systems(i.e.,the progenitor systems of AIC events)could potentially be identified as supersoft X-ray sources,symbiotics and cataclysmic variables(such as classical novae,recurrent novae,Ne novae and He novae)in the observations,whereas the post-AIC systems(i.e.,NS systems)could potentially be identified as low-/intermediate-mass X-ray binaries,and the resulting low-/intermediate-mass binary pulsars,most notably millisecond pulsars.For the double-degenerate model,the pre-AIC systems are close double WDs with short orbital periods,whereas the post-AIC systems are single isolated NSs that may correspond to a specific kind of NS with peculiar properties.We also review the predicted rates of AIC events,the mass distribution of NSs produced via AIC and the gravitational wave(GW)signals from double WDs that are potential GW sources in the Galaxy in the context of future spacebased GW detectors,such as LISA,TianQin,Taiji,etc.Recent theoretical and observational constraints on the detection of AIC events are summarized.In order to confirm the existence of the AIC process,and resolve this long-term issue presented by current stellar evolution theories,more numerical simulations and observational identifications are required.
基金support from the National Natural Science Foundation of China (Grant Nos.W820301904 and 12033005)。
文摘To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) telescope.Based on the observations of APEX,we obtain luminosity to mass ratios Lclump/Mclump that range from 10 to 154 L_(⊙)/M_(⊙),where some of them embedded ultra compact(UC) H Ⅱ region.Using the SMA,CH3CN(12K-11K) transitions were observed toward nine massive starforming regions.We derive the CH3CN rotational temperature and column density using the XCLASS program,and calculate its fractional abundance.We find that CH3CN temperature seems to increase with the increase of Lclump/Mclump when the ratio is between 10 to 40 L_(⊙)/M_(⊙),then decrease when L_(clump)/M_(clump)≥ 40 L_(⊙)/M_(⊙).Assuming that the CH3CN gas is heated by radiation from the central star,the effective distance of CH3CN relative to the central star is estimated.The distance ranges from - 0.003 to - 0.083 pc,which accounts for - 1/100 to - 1/1000 of clump size.The effective distance increases slightly as Lclump/Mclump increases(Reff-(L_(clump)/M_(clump))0.5±0.2).Overall,the CH3 CN abundance is found to decrease as the clumps evolve,e.g.,XCH3CN -(L_(clump)/M_(clump))-1.0±0.7.The steady decline of CH3CN abundance as the clumps evolution can be interpreted as a result of photodissociation.
基金Supported by the National Natural Science Foundation of China though Grants 10173021, 10433030,10773003 and 10778601supported by the Ministry of Science and Technology of the People’s Republic of China through Grant 2007CB815406
文摘We investigate the rotation profile of solar-like stars with magnetic fields. A diffu- sion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the coefficient are computed to give the rotation profiles. The total angular momentum of a solar model with only hydrodynamic instabilities is about 13 times larger than that of the Sun at the age of the Sun, and this model can not reproduce quasi-solid rotation in the radiative region. However, the solar model with magnetic fields not only can reproduce an almost uniform rotation in the radiative region, but also a total angular momentum that is consistent with the helioseismic result at the 3 tr level at the age of the Sun. The rotation of solar-like stars with magnetic fields is almost uniform in the radiative region, but for models of 1.2-1.5 MG, there is an obvious transition region between the convective core and the radiative region, where angular velocity has a sharp radial gradient, which is different from the rotation profile of the Sun and of massive stars with magnetic fields. The change of angular velocity in the transition region increases with increasing age and mass.
基金partly supported by the National RI Roadmap Project(contracts D01-383/18.12.2020 and D01-176/29.07.2022)of the Ministry of Education and Science of the Republic of Bulgaria。
文摘In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported.The star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia.V1180 Cas shows large amplitude variability,interpreted as a combination of accretion-induced and extinction-driven effects.Our data from VRI CCD photometric observations of the star were collected from September 2011 to February 2022.During our monitoring,we recorded several brightness dips with large amplitudes of up to 5 mag(I band).At the same time,increases in brightness over periods of several weeks have also been recorded.In this paper,we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.
基金supported by the CAS‘Light of West China’Program(Grant No.2018-XBQNXZ-B-022)the National Natural Science Foundation of China(Grant Nos.11803018,11733009,11773015,U2031116 and 11605110)+2 种基金the National Key Research and Development Program of China(Grant No.2016YFA0400803)the Program for Innovative Research Team(in Science and Technology)at the University of Henan Provincethe Key laboratory of Modern Astronomy and Astrophysics(Nanjing University),Ministry of Education。
文摘PSR J1946+3417 is a millisecond pulsar(MSP)with a spin period P?3.17 ms.Harbored in a binary with an orbital period Pb?27 days,the MSP is accompanied by a white dwarf(WD).The masses of the MSP and the WD were determined to be 1.83 M⊙,and 0.266 M⊙,respectively.Specially,its orbital eccentricity is e?0.134,which is challenging the recycling model of MSPs.Assuming that the neutron star in a binary may collapse to a strange star when its mass reaches a critical limit,we propose a phase transition(PT)scenario to account for the origin of the system.The sudden mass loss and the kick induced by asymmetric collapse during the PT may result in the orbital eccentricity.If the PT event takes place after the mass transfer ceases,the eccentric orbit cannot be re-circularized in the Hubble time.Aiming at the masses of both components,we simulate the evolution of the progenitor of PSR J1946+3417 via MESA.The simulations show that an NS/main sequence star binary with initial masses of 1.4+1.6 M⊙in an initial orbit of 2.59 days will evolve into a binary consisting of a 2.0 M⊙MSP and a 0.27 M⊙WD in an orbit of~21.5 days.Assuming that the gravitational mass loss fraction during PT is 10%,we simulate the effect of PT via the kick program of BSE with a velocity ofσPT=60 km s-1.The results show that the PT scenario can reproduce the observed orbital period and eccentricity with higher probability than other values.
基金support from the National Natural Science Foundation of China(NSFC)(Nos.12005124 and 12147215)support from the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(STIP)(No.2020L0528)the Applied Basic Research Programs of Natural Science Foundation of Shanxi Province(No.202103021223320)。
文摘In this work,the pulsation analysis is performed on 83 high-amplitudeδScuti stars(HADS),which have been observed by the Transiting Exoplanet Survey Satellite.The results show that 49 of these HADS show single-mode pulsation,27 of them show radial double-modes pulsation(in which 22 of them pulsate with the fundamental and first overtone modes and five of them pulsate with the first and second overtone modes),and seven of them show radial triple-modes pulsation(three of which are newly confirmed triple-mode HADS).The histogram of the fundamental periods and the ratios between the fundamental and first overtone periods show bimodal structures,which might be caused by the stellar evolution in this specific phase.Most of the radial triple-mode HADS have a fundamental amplitude of 41-54 mmag,and 50%of them have similar amplitudes of the fundamental and first overtone pulsation modes.All these hints require further confirmation not only in observations with more HADS samples,but also in theoretical models with suitable treatments of stellar evolution and pulsation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11933008 and 11903076)the Science Foundation of Yunnan Province (202001AT070051)+1 种基金the Foundation of Science and Technology of Guizhou Province (Nos. (2016)4008, (2017)5726-37)the Foundation of Guizhou Provincial Education Department (No. KY(2020)003)。
文摘Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is an A-subtype contact binary with low mass ratio(q = 0.178) while NW Leo has a high mass ratio(q = 0.707). For CSS J075415.6+191052, the RI light curves show weakening around the left shoulder of the secondary minimum, which indicates that there may be a dark spot on the secondary component. However, the light curves of BV bands are totally symmetric. It is unreasonable if the dark spot is caused by magnetic activity or mass transfer between the two components. Therefore, weakening of the light curves in this contact binary is caused by something else. A possible explanation is mass transferring from the primary component to the common convective envelope through the inner Lagrangian point, and this part of the mass, for some reason, weakens the RI bands of light from the secondary component. O-C analysis of NW Leo reveals a cyclic period change with a modulation period of 4.7 yr, which may be caused by the light travel time effect of a third body. The positions of CSS J075415.6+191052 and NW Leo in the P–J′_(orb)diagram indicate that CSS J075415.6+191052 mainly abides by the angular momentum loss theory while NW Leo is dominated by the thermal relaxation oscillation theory.
文摘Using Eggleton＇s code, we systematically show the differences in stellar evolution between the results based on the scaled-solar mixture and the a-enhanced metal mixture. As input, the OPAL high temperature opacities are used for log（T/K） 〉 4.00, and the new Wichita State low temperature opacities, for log（T/K） ≤ 4.00, Our calculations cover star masses ranging from 0.25 to 80.0M⊙, spaced at ΔlogM = 0.10 or 0.05. The values of metallicities Z are 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08 and 0.10. For a given Z, the initial hydrogen mass fraction is given by X = 0.76 - 3.0Z. We show that a-enhancement can raise the stellar effective temperature and luminosity, and reduce the evolutionary age. Compared with some previous work, the effects of α-enhancement are more obviously demonstrated in our calculations.
