The subsurface convective zones (CZs) of massive stars significantly influence many of their key characteristics.Previous studies have paid little attention to the impact of rotation on the subsurface CZ,so we aim to ...The subsurface convective zones (CZs) of massive stars significantly influence many of their key characteristics.Previous studies have paid little attention to the impact of rotation on the subsurface CZ,so we aim to investigate the evolution of this zone in rapidly rotating massive stars.We use the Modules for Experiments in Stellar Astrophysics to simulate the subsurface CZs of massive stars during the main sequence phase.We establish stellar models with initial masses ranging from 5 M⊙to 120 M⊙,incorporating four metallicities (Z=0.02,0.006,0.002,and 0.0001) and three rotational velocities (ω/ωcrit=0,ω/ωcrit=0.50,andω/ωcrit=0.75).We find that rapid rotation leads to an expansion of the subsurface CZ,increases convective velocities,and promotes the development of this zone.Additionally,subsurface CZs can also emerge in stars with lower metallicities.Comparing our models with observations of massive stars in the Galaxy,the Large Magellanic Cloud,and the Small Magellanic Cloud,we find that rotating models better encompass the observed samples.Rotation significantly influences the evolution of the subsurface CZ in massive stars.By comparing with the observed microturbulence on the surfaces of OB stars,we propose that the subsurface CZs may be one of the sources of microturbulence.展开更多
The best way to check the validity of our theories(models)is by direct comparison with the experiment(observations).However,this process suffers from numerical inaccuracies,which are not frequently studied and often r...The best way to check the validity of our theories(models)is by direct comparison with the experiment(observations).However,this process suffers from numerical inaccuracies,which are not frequently studied and often remain mostly unknown.In this study,we focus on addressing the numerical inaccuracies intrinsic to the process of comparing theory and observations.To achieve this goal,we built four-dimensional(4D)spectral grids for Wolf–Rayet stars(WC and WN spectral classes)and blue supergiants characterized by low metallicity similar to that of the Small Magellanic Cloud.In contrast to lighter(three-dimensional)grids,which rely on a priori assumptions about certain stellar parameters(e.g.,wind velocity)and thus have limited applicability,our 4D grids vary four independent parameters,enabling more flexible and broadly applicable spectral fitting.Utilizing these 4D grids,we developed and validated a fitting approach facilitating direct fits to observed spectra.Through rigorous testing on designated“test”models,we demonstrated that the numerical precision of derived essential stellar parameters,including effective temperature,mass-loss rate,luminosity,and wind velocity,is better than 0.05 dex.Furthermore,we explored the influence of unaccounted factors,including variations in the metal abundances,wind acceleration laws,and clumping,on the precision of the derived parameters.The results indicate that the first two factors have the strongest influence on the numerical accuracy of the derived stellar parameters.Variations in abundances predominantly influenced the mass-loss rate for weak-wind scenarios,while effective temperature and luminosity remained robust.We found that the wind acceleration law influences the numerical uncertainty of the derived wind parameters mostly for models with weak winds.Interestingly,different degrees of clumping demonstrated good precision for spectra with strong winds,contrasting with a decrease in the precision for weak-wind cases.We found also that the accuracy of our approach depends on spectral range and the inclusion of ultraviolet spectral range improves the precision of derived parameters,especially for an object with weak winds.展开更多
Binary systems in the asymptotic giant branch(AGB)phase are widely recognized as a leading theoretical framework underpinning the observed asymmetric morphologies of planetary nebulae.However,the detection of binary c...Binary systems in the asymptotic giant branch(AGB)phase are widely recognized as a leading theoretical framework underpinning the observed asymmetric morphologies of planetary nebulae.However,the detection of binary companions in AGB systems is severely hampered by the overwhelming brightness and variability of the evolved primary star,which dominates the photometric and spectroscopic signatures.Ultraviolet(UV)excess emission has been proposed as a candidate diagnostic for the presence of binary companions in AGB systems.This paper evaluates the Chinese Space Station Telescope’s(CSST)ability to detect UV excess emission in AGB stars,leveraging its unprecedented UV sensitivity and wide-feld survey capabilities.We employed synthetic spectral libraries of M0–M8 type giants for primary stars and the ATLAS 9 atmospheric model grid for companion stars spanning a temperature range of 6500 to 12,000 K.By convolving these model spectra with the CSST multi-band flter system,we computed color–color diagrams(g–y versus NUV–u)to construct a diagnostic grid.This grid incorporates interstellar extinction corrections and establishes a framework for identifying AGB binary candidates through direct comparison between observed photometry and theoretical predictions.Furthermore,we discuss the physical origins of UV excess in AGB stars.This study pioneers a diagnostic framework leveraging CSST’s unique multi-band UV-visible synergy to construct color–color grids for binary candidate identifcation,overcoming limitations of non-simultaneous multi-instrument observations.展开更多
δScuti(δSct)stars are potential distance tracers for studying the Milky Way structure.We conduct a comprehensive analysis of the period-luminosity(PL)and period-luminosity-metallicity(PLZ)relations forδSct stars,in...δScuti(δSct)stars are potential distance tracers for studying the Milky Way structure.We conduct a comprehensive analysis of the period-luminosity(PL)and period-luminosity-metallicity(PLZ)relations forδSct stars,integrating data from the Zwicky Transient Facility,the Transiting Exoplanet Survey Satellite,Large Sky Area Multi-Object Fiber Spectroscopic Telescope,Apache Point Observatory Galactic Evolution Experiment,and Gaia.To mitigate the impact of the Gaia parallax zero point offset,we applied a correction method,determining the optimal zero point value to be zp(?)=35±2μas.Using the three best bands,by varying the parallax error threshold,we found that the total error of the PLR zero point was minimized to 0.9%at a parallax error threshold of 6%.With this threshold,we derived the PL and PLZ relations for nine bands(from optical to mid-infrared)and five Wesenheit bands.Through our analysis,we conclude that the influence of metallicity on the PLR ofδSct stars is not significant,and the differences across various bands are minimal.展开更多
With a one-dimensional stellar evolution model,we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from t...With a one-dimensional stellar evolution model,we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion.We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones.These jets remove the outer high-entropy layers of the mass-accreting star.This process operates in a negative feedback cycle,as the jets remove more envelope mass when the star expands.With the one-dimensional model,we mimic the mass removal by jets by alternating mass addition and mass removal phases.For the simulated models of 30M☉and 60M☉,the star does not expand much if we remove more than about half of the added mass in not-too-short episodes.This holds even if we deposit the energy the jets do not carry into the envelope.As the star does not expand much,its gravitational potential well stays deep,and the jets are energetic.These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets,e.g.,intermediate luminosity optical transients,including some luminous red novae,the grazing envelope evolution,and the 1837–1856 Great Eruption of Eta Carinae.展开更多
Based on positional observations and measurements of radial velocities,the orbits of 850 wide visual binary stars have been determined.The parameters of the log-normal distributions for the histograms of orbital perio...Based on positional observations and measurements of radial velocities,the orbits of 850 wide visual binary stars have been determined.The parameters of the log-normal distributions for the histograms of orbital periods,stellar masses,and semimajor axes in astronomical units have been obtained.The eccentricity histogram for binary stars with orbital periods less than 400 yr follows a normal distribution centered at e=0.545+/−0.029.For stars with longer periods,this distribution obeys the law f=2e,with accuracy to errors.The mass-to-luminosity relation for stars with well-determined masses is given by:log L_(⊙)=4.33 logM_(⊙)-0.11,where L_(⊙) and M_(⊙) are the luminosity and mass of the star in units of the solar luminosity and mass,respectively.展开更多
The study of carbon-enhanced metal-poor (CEMP) stars is of great significance for understanding the chemical evolution of the early universe and stellar formation.CEMP stars are characterized by carbon overabundance a...The study of carbon-enhanced metal-poor (CEMP) stars is of great significance for understanding the chemical evolution of the early universe and stellar formation.CEMP stars are characterized by carbon overabundance and are classified into several subclasses based on the abundance patterns of neutron-capture elements,including CEMP-s,CEMP-no,CEMP-r,and CEMP-r/s.These subclasses provide important insights into the formation of thefirst stars,early stellar nucleosynthesis,and supernova explosions.However,one of the major challenges in CEMP star research is the relatively small sample size of identified stars,which limits statistical analyses and hinders a comprehensive understanding of their properties.Fortunately,a series of large-scale spectroscopic survey projects have been launched and developed in recent years,providing unprecedented opportunities and technical challenges for the search and study of CEMP stars.To this end,this paper draws on the progress and future prospects of existing methods in constructing large CEMP data sets and offers an in-depth discussion from a technical standpoint,focusing on the strengths and limitations.In addition,we review recent advancements in the identification of CEMP stars,emphasizing the growing role of machine learning in processing and analyzing the increasingly large data sets generated by modern astronomical surveys.Compared to traditional spectral analysis methods,machine learning offers greater efficiency in handling complex data,automatic extraction of stellar parameters,and improved prediction accuracy.Despite these advancements,the research faces persistent challenges,including the scarcity of labeled samples,limitations imposed by low-resolution spectra,and the lack of interpretability in machine learning models.To address these issues,the paper proposes potential solutions and future research directions aimed at advancing the study of CEMP stars and enhancing our understanding of their role in the chemical evolution of the universe.展开更多
Accurate determinations of metallicity for large,complete stellar samples are essential for advancing various studies of the Milky Way.In this paper,we present a data-driven algorithm that leverages photometric data f...Accurate determinations of metallicity for large,complete stellar samples are essential for advancing various studies of the Milky Way.In this paper,we present a data-driven algorithm that leverages photometric data from the KiDS and the VIKING surveys to estimate stellar absolute magnitudes,effective temperatures,and metallicities.The algorithm is trained and validated using spectroscopic data from LAMOST,SEGUE,APOGEE,and GALAH,as well as a catalog of very metal-poor stars from the literature,and Gaia EDR3 data.This approach enables us to estimate metallicities,effective temperatures,and g-band absolute magnitudes for approximately 0.8 million stars in the KiDS data set.The photometric metallicity estimates exhibit an uncertainty of around 0.28 dex when compared to spectroscopic studies,within the metallicity range of−2 dex to 0.5 dex.The photometric effective temperature estimates have an uncertainty of around 149 K,while the uncertainty in the absolute magnitudes is approximately 0.36 mag.The metallicity estimates are reliable for values down to about−2 dex.This catalog represents a valuable resource for studying the structure and chemical properties of the Milky Way,offering an extensive data set for future investigations into Galactic formation and evolution.展开更多
Red clump(RC)stars are reliable standard candles for studying the structure and evolution of the Milky Way.In this study,we present empirical calibrations of RC absolute magnitudes in the Mephisto(v,g,r,i)and CSST(g,r...Red clump(RC)stars are reliable standard candles for studying the structure and evolution of the Milky Way.In this study,we present empirical calibrations of RC absolute magnitudes in the Mephisto(v,g,r,i)and CSST(g,r,i)photometric systems using a high-purity sample of 25,059 RC stars cross-matched between APOGEE and Gaia DR3 XP spectra.Through synthetic photometry and polynomial fitting,we find that RC absolute magnitudes exhibit strong dependencies on effective temperature and metallicity,with the strongest variations observed in bluer bands and progressively decreasing towards redder wavelengths.In particular,the Mephisto v band exhibits the highest sensitivity,with variations reaching up to 2.0 mag across the metallicity range(−1.0 dex<[Fe/H]<0.5 dex)and the temperature range(4500–5200 K).The calibrations achieve high precision for all bands,enabling accurate determination of RC absolute magnitudes and distances.Furthermore,we evaluate the metallicity estimation capabilities of both systems using a Random Forest-based method,achieving a precision of 0.12 dex for Mephisto and 0.14 dex for CSST under typical photometric uncertainties(≤0.01 mag).These results provide robust tools for distance and metallicity determinations,supporting future Galactic structure studies with Mephisto and CSST data.展开更多
We present optical spectra of 10 Galactic Wolf-Rayet(WR)stars that consist of five WN and five WC stars.The optical observation was conducted using a low-resolution spectrograph NEO-R1000(λ/Δλ~1000)at GAO-ITB RTS(2...We present optical spectra of 10 Galactic Wolf-Rayet(WR)stars that consist of five WN and five WC stars.The optical observation was conducted using a low-resolution spectrograph NEO-R1000(λ/Δλ~1000)at GAO-ITB RTS(27.94 cm,F/10.0),Bosscha Observatory,Lembang.We implemented stellar atmosphere Postdam Wolf-Rayet(PoWR)grid modeling to derive stellar parameters.The normalized optical spectrum can be used to find the best model from the available PoWR grid,then we could derive stellar temperature and transformation radius.To derive luminosity,stellar radius and color excess,we conducted a Spectral Energy Distribution(SED)analysis with additional data on the near-ultraviolet spectrum from the International Ultraviolet Explorer(IUE)database,and UBV and 2MASS JHK broadband filter data.Additional analysis to derive asymptotic terminal wind velocity was conducted from the P-Cygni profile analysis of the high-resolution IUE ultraviolet spectrum.With previously derived parameters,we could determine the mass loss rate of the WR stars.Furthermore,we compared our results with previous work that used PoWR code and the differences are not more than 20%.We conclude that the PoWR spectral grid is sufficient to derive WR stellar parameters quickly and could provide more accurate initial parameter input to the PoWR program code.展开更多
The emission of anomalous X-ray pulsars(AXPs)and soft gamma-ray repeaters(SGRs)is believed to be powered by the dissipation of their strong magnetic fields,which coined the name“magnetar”.By combining timing and ene...The emission of anomalous X-ray pulsars(AXPs)and soft gamma-ray repeaters(SGRs)is believed to be powered by the dissipation of their strong magnetic fields,which coined the name“magnetar”.By combining timing and energy observational results,the magnetar model can be easily appreciated.From a timing perspective,the magnetic field strengths of AXPs and SGRs,which are calculated under the assumption of dipole radiation,are extremely strong.From an energy perspective,the X-ray/soft gamma-ray luminosities of AXPs and SGRs are larger than their rotational energy loss rates(i.e.,L_(x>E_(rot)).It is thus reasonable to assume that the high-energy radiation comes from magnetic energy decay,and the magnetar model has been extensively discussed(or accepted).However,we argue that:(ⅰ)Calculating magnetic fields by assuming that rotational energy loss is dominated by dipole radiation(i.e.,E_(rot)■E_(μ))may be controversial,and we suggest that the energies carried by outflowing particles should also be considered.(ⅱ)The fact that X-ray luminosity is greater than the rotational energy loss rate does not necessarily mean that the emission energy comes from the magnetic field decaying,which requires further observational testing.Furthermore,some observational facts conflict with the“magnetar”model,such as observations of anti-magnetars,high magnetic field pulsars,and radio and X-ray observations of AXPs/SGRs.Therefore,we propose a crusted strange star model as an alternative,which can explain many more observational facts of AXPs/SGRs.展开更多
We present a theoretical model for detecting axions from neutron stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair uu¯or dd¯, in loop(s) involving gluons. The chi...We present a theoretical model for detecting axions from neutron stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair uu¯or dd¯, in loop(s) involving gluons. The chiral anomaly of QCD and the spontaneously broken symmetry are invoked to explain the non-conservation of the axion current. From the coupling form factors, the axion emissivities ϵacan be derived, from which fluxes can be determined. We predict a photon flux, which may be detectable by Fermi LAT, and limits on the QCD mass ma. In this model, axions decay to gamma rays in a 2-photon vertex. We may determine the expected fluxes from the theoretical emissivity. The sensitivity curve from the Fermi Large Area Telescope (Fermi LAT) would allow axion mass constraints for neutron stars as low as ma≤10−14eV 95% C.L. Axions could thus be detectable in gamma rays for neutron stars as distant as 100 kpc. A signal from LIGO GWS 170817 could be placed from the NS-NS merger, which gives an upper limit of ma≤10−10eV.展开更多
Hot subdwarf stars are important celestial objects in the study of stellar physics,but the population remains limited.The LAMOST DR12-V1,released in 2025 March,is currently the world’s largest spectroscopic database,...Hot subdwarf stars are important celestial objects in the study of stellar physics,but the population remains limited.The LAMOST DR12-V1,released in 2025 March,is currently the world’s largest spectroscopic database,holding great potential for the search of hot subdwarf stars.In this study,we propose a two-stage deep learning model called the hot subdwarf network(HsdNet),which integrates multiple advanced techniques,comprising a binary classification model in stage one and a five-class classification model in stage two.HsdNet not only achieves high precision with 94.33%and 94.00%in the binary and the five-class classification stages,respectively,but also quantifies the predicted uncertainty,enhancing the interpretability of the classification results through visualizing the model’s key focus regions.We applied HsdNet to the 601,217 spectra from the LAMOST DR12-V1 database,conducting a two-stage search for hot subdwarf candidates.In stage one,we initially identified candidates using the binary classification model.In stage two,the five-class classification model was used to further refine these candidates.Finally,we confirmed 1008 newly identified hot subdwarf stars.The distribution of their atmospheric parameters is consistent with that of known hot subdwarf stars.These efforts are expected to significantly advance the research on hot subdwarf stars.展开更多
在2025釜山国际广告节New Stars全球青年创意竞赛的领奖台上,来自省广集团的苏粤与搭档吕一潇的欢呼格外响亮。这对因连续几次在比赛中获得银奖而自我调侃为“千年老二”的搭档,终于以《THE AI ACCESS CARD》的创意作品拿下金奖。她们...在2025釜山国际广告节New Stars全球青年创意竞赛的领奖台上,来自省广集团的苏粤与搭档吕一潇的欢呼格外响亮。这对因连续几次在比赛中获得银奖而自我调侃为“千年老二”的搭档,终于以《THE AI ACCESS CARD》的创意作品拿下金奖。她们的故事藏着新一代广告人对创意、行业与技术的思考。展开更多
Research on the properties of neutron stars with dark energy is a particularly interesting yet unresolved problem in astrophysics.We analyze the influence of dark energy on the equation of state,the maximum mass,the s...Research on the properties of neutron stars with dark energy is a particularly interesting yet unresolved problem in astrophysics.We analyze the influence of dark energy on the equation of state,the maximum mass,the surface gravitational redshift and the Keplerian frequency for the traditional neutron star and the hyperon star matter within the relativistic mean field theory,using the GM1 and TM1 parameter sets by considering the two flavor symmetries of SU(6)and SU(3)combined with the observations of PSR J1614-2230,PSR J0348+0432,PSR J0030+0451,RX J0720.4-3125,and 1E 1207.4-5209.It is found that the existence of dark energy leads to the softened equations of the state of the traditional neutron star and the hyperon star.The radius of a fixed-mass traditional neutron star(or hyperon star)with dark energy becomes smaller,which leads to increased compactness.The existence of dark energy can also enhance the surface gravitational redshift and the Keplerian frequency of traditional neutron stars and hyperon stars.The growth of the Keplerian frequency may cause the spin rate to speed up,which may provide a possible way to understand and explain the pulsar glitch phenomenon.Specifically,we infer that the mass and the surface gravitational redshift of PSR J1748-2446ad without dark energy for the GM1(TM1)parameter set are 1.141 M_(☉)(1.309 M_(☉))and 0.095(0.105),respectively.The corresponding values for the GM1(TM1)parameter set are 0.901 M_(☉)(1.072M_(☉))and 0.079(0.091)if PSR J1748-2446ad contains dark energy withα=0.05.PSR J1748-2446ad may be a low-mass pulsar with a lower surface gravitational redshift under our selected models.展开更多
The spinning-up of the accreting component in the process of conservative mass exchange is considered in binary systems—progenitors of systems consisting of a main sequence Be-star and an O-subdwarf.During the mass e...The spinning-up of the accreting component in the process of conservative mass exchange is considered in binary systems—progenitors of systems consisting of a main sequence Be-star and an O-subdwarf.During the mass exchange,the meridional circulation transfers 80%-85%of the angular momentum that entered the accretor together with the accreted matter to the accretor surface.This angular momentum is removed from the accretor by the disk.When the mass exchange finishes,the accretor has a rotation typical of classical Be-type stars.展开更多
With the advancement of astronomical observation technology,people have a deeper understanding of the formation and evolution of galaxies,but many details of our own Milky Way and other external galaxies are still unk...With the advancement of astronomical observation technology,people have a deeper understanding of the formation and evolution of galaxies,but many details of our own Milky Way and other external galaxies are still unknown.Therefore,by studying the formation and orbital transformation mechanism of satellites,planets and stars,the author puts forward a new theory on the formation and evolution of stars and galaxies,thus revealing the hierarchical structure of galaxies and the formation and evolution laws of main sequence stars,red giants,white dwarfs,black dwarfs,supernovae,neutron stars,black holes and quasars.Some special phenomena in the course of star formation and evolution,such as sunspots,flares,fast radio bursts and gamma-ray bursts,have also been revealed.展开更多
In the present article,we introduce a completely new regular model for static,spherically symmetric celestial fluid spheres in embedding classⅠspacetime.In this regard,needfully,we propose a new suitable metric poten...In the present article,we introduce a completely new regular model for static,spherically symmetric celestial fluid spheres in embedding classⅠspacetime.In this regard,needfully,we propose a new suitable metric potential e^(λ(r))to generate the present model.The various analyses on energy density,pressure,anisotropic factor,mass,compactness parameter,redshift,and energy condition make sure the model is physically viable on the ground of model stars Vela X-1,Cen X-3,SMC X-4,and LMC X-4.The reported solutions also respect the equilibrium state by satisfying the Tolman-Oppenheimer-Volkoff(TOV)equation and ensure stability by satisfying the causality condition,condition on the adiabatic index,and Harrison-Zeldovich-Novikov condition.The generated M-R graph matches the ranges of masses and radii for the model compact stars.Additionally,this study provides estimates of the moment of inertia based on the I-M graph.展开更多
Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate...Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate.Enormous energy is surely needed to understand various observations,such asγ-ray bursts,fast radio bursts and softγ-ray repeaters.In this paper,the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars,with two anisotropic models to calculate in general relativity.It is found that huge free energy(>10^(46)erg)could be released via starquakes,given an extremely small anisotropy((p_(t)-p_(r))/p_(r)~10^(-4),with pt/pr the tangential/radial pressure),implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.展开更多
基金the National Natural Science Foundation of China under grant Nos.U2031204,12163005,12373038,12288102,and 12263006the science research grant from the China Manned Space Project with No.CMSCSST-2021-A10+1 种基金the Natural Science Foundation of Xinjiang Nos.2022D01D85 and 2022TSYCLJ0006the Major Science and Technology Program of Xinjiang Uygur Autonomous Region under grant No.2022A03013-3.
文摘The subsurface convective zones (CZs) of massive stars significantly influence many of their key characteristics.Previous studies have paid little attention to the impact of rotation on the subsurface CZ,so we aim to investigate the evolution of this zone in rapidly rotating massive stars.We use the Modules for Experiments in Stellar Astrophysics to simulate the subsurface CZs of massive stars during the main sequence phase.We establish stellar models with initial masses ranging from 5 M⊙to 120 M⊙,incorporating four metallicities (Z=0.02,0.006,0.002,and 0.0001) and three rotational velocities (ω/ωcrit=0,ω/ωcrit=0.50,andω/ωcrit=0.75).We find that rapid rotation leads to an expansion of the subsurface CZ,increases convective velocities,and promotes the development of this zone.Additionally,subsurface CZs can also emerge in stars with lower metallicities.Comparing our models with observations of massive stars in the Galaxy,the Large Magellanic Cloud,and the Small Magellanic Cloud,we find that rotating models better encompass the observed samples.Rotation significantly influences the evolution of the subsurface CZ in massive stars.By comparing with the observed microturbulence on the surfaces of OB stars,we propose that the subsurface CZs may be one of the sources of microturbulence.
文摘The best way to check the validity of our theories(models)is by direct comparison with the experiment(observations).However,this process suffers from numerical inaccuracies,which are not frequently studied and often remain mostly unknown.In this study,we focus on addressing the numerical inaccuracies intrinsic to the process of comparing theory and observations.To achieve this goal,we built four-dimensional(4D)spectral grids for Wolf–Rayet stars(WC and WN spectral classes)and blue supergiants characterized by low metallicity similar to that of the Small Magellanic Cloud.In contrast to lighter(three-dimensional)grids,which rely on a priori assumptions about certain stellar parameters(e.g.,wind velocity)and thus have limited applicability,our 4D grids vary four independent parameters,enabling more flexible and broadly applicable spectral fitting.Utilizing these 4D grids,we developed and validated a fitting approach facilitating direct fits to observed spectra.Through rigorous testing on designated“test”models,we demonstrated that the numerical precision of derived essential stellar parameters,including effective temperature,mass-loss rate,luminosity,and wind velocity,is better than 0.05 dex.Furthermore,we explored the influence of unaccounted factors,including variations in the metal abundances,wind acceleration laws,and clumping,on the precision of the derived parameters.The results indicate that the first two factors have the strongest influence on the numerical accuracy of the derived stellar parameters.Variations in abundances predominantly influenced the mass-loss rate for weak-wind scenarios,while effective temperature and luminosity remained robust.We found that the wind acceleration law influences the numerical uncertainty of the derived wind parameters mostly for models with weak winds.Interestingly,different degrees of clumping demonstrated good precision for spectra with strong winds,contrasting with a decrease in the precision for weak-wind cases.We found also that the accuracy of our approach depends on spectral range and the inclusion of ultraviolet spectral range improves the precision of derived parameters,especially for an object with weak winds.
基金supports of this work are from the science research grants from the China Manned Space Project(NOs.CMSCSST-2021-A09,CMS-CSST-2021-A10,etc.)the National Natural Science Foundation of China(NSFC,Nos.12473027 and 12333005)the Guangdong Basic and Applied Basic Research Funding(No.2024A1515010798).
文摘Binary systems in the asymptotic giant branch(AGB)phase are widely recognized as a leading theoretical framework underpinning the observed asymmetric morphologies of planetary nebulae.However,the detection of binary companions in AGB systems is severely hampered by the overwhelming brightness and variability of the evolved primary star,which dominates the photometric and spectroscopic signatures.Ultraviolet(UV)excess emission has been proposed as a candidate diagnostic for the presence of binary companions in AGB systems.This paper evaluates the Chinese Space Station Telescope’s(CSST)ability to detect UV excess emission in AGB stars,leveraging its unprecedented UV sensitivity and wide-feld survey capabilities.We employed synthetic spectral libraries of M0–M8 type giants for primary stars and the ATLAS 9 atmospheric model grid for companion stars spanning a temperature range of 6500 to 12,000 K.By convolving these model spectra with the CSST multi-band flter system,we computed color–color diagrams(g–y versus NUV–u)to construct a diagnostic grid.This grid incorporates interstellar extinction corrections and establishes a framework for identifying AGB binary candidates through direct comparison between observed photometry and theoretical predictions.Furthermore,we discuss the physical origins of UV excess in AGB stars.This study pioneers a diagnostic framework leveraging CSST’s unique multi-band UV-visible synergy to construct color–color grids for binary candidate identifcation,overcoming limitations of non-simultaneous multi-instrument observations.
基金supported by the National Natural Science Foundation of China(NSFC)through grants 12173047,12373035,12322306,12373028,12233009 and 12133002X.C.and S.W.acknowledge supports from the Youth Innovation Promotion Association of the Chinese Academy of Sciences(CAS,Nos.2022055 and 2023065)+2 种基金support from the National Key Research and Development Program of China,grant 2022YFF0503404Funding for the DPAC has been provided by national institutions,in particular the institutions participating in the Gaia Multilateral AgreementFunding for the project has been provided by the National Development and Reform Commission。
文摘δScuti(δSct)stars are potential distance tracers for studying the Milky Way structure.We conduct a comprehensive analysis of the period-luminosity(PL)and period-luminosity-metallicity(PLZ)relations forδSct stars,integrating data from the Zwicky Transient Facility,the Transiting Exoplanet Survey Satellite,Large Sky Area Multi-Object Fiber Spectroscopic Telescope,Apache Point Observatory Galactic Evolution Experiment,and Gaia.To mitigate the impact of the Gaia parallax zero point offset,we applied a correction method,determining the optimal zero point value to be zp(?)=35±2μas.Using the three best bands,by varying the parallax error threshold,we found that the total error of the PLR zero point was minimized to 0.9%at a parallax error threshold of 6%.With this threshold,we derived the PL and PLZ relations for nine bands(from optical to mid-infrared)and five Wesenheit bands.Through our analysis,we conclude that the influence of metallicity on the PLR ofδSct stars is not significant,and the differences across various bands are minimal.
基金A grant from the Pazy Foundation supported this research.
文摘With a one-dimensional stellar evolution model,we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion.We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones.These jets remove the outer high-entropy layers of the mass-accreting star.This process operates in a negative feedback cycle,as the jets remove more envelope mass when the star expands.With the one-dimensional model,we mimic the mass removal by jets by alternating mass addition and mass removal phases.For the simulated models of 30M☉and 60M☉,the star does not expand much if we remove more than about half of the added mass in not-too-short episodes.This holds even if we deposit the energy the jets do not carry into the envelope.As the star does not expand much,its gravitational potential well stays deep,and the jets are energetic.These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets,e.g.,intermediate luminosity optical transients,including some luminous red novae,the grazing envelope evolution,and the 1837–1856 Great Eruption of Eta Carinae.
基金support of the Russian Foundation for Basic Research under Contract No.20-02-00563A.
文摘Based on positional observations and measurements of radial velocities,the orbits of 850 wide visual binary stars have been determined.The parameters of the log-normal distributions for the histograms of orbital periods,stellar masses,and semimajor axes in astronomical units have been obtained.The eccentricity histogram for binary stars with orbital periods less than 400 yr follows a normal distribution centered at e=0.545+/−0.029.For stars with longer periods,this distribution obeys the law f=2e,with accuracy to errors.The mass-to-luminosity relation for stars with well-determined masses is given by:log L_(⊙)=4.33 logM_(⊙)-0.11,where L_(⊙) and M_(⊙) are the luminosity and mass of the star in units of the solar luminosity and mass,respectively.
基金supported by the National Natural Science Foundation of China (grant No.12373108)。
文摘The study of carbon-enhanced metal-poor (CEMP) stars is of great significance for understanding the chemical evolution of the early universe and stellar formation.CEMP stars are characterized by carbon overabundance and are classified into several subclasses based on the abundance patterns of neutron-capture elements,including CEMP-s,CEMP-no,CEMP-r,and CEMP-r/s.These subclasses provide important insights into the formation of thefirst stars,early stellar nucleosynthesis,and supernova explosions.However,one of the major challenges in CEMP star research is the relatively small sample size of identified stars,which limits statistical analyses and hinders a comprehensive understanding of their properties.Fortunately,a series of large-scale spectroscopic survey projects have been launched and developed in recent years,providing unprecedented opportunities and technical challenges for the search and study of CEMP stars.To this end,this paper draws on the progress and future prospects of existing methods in constructing large CEMP data sets and offers an in-depth discussion from a technical standpoint,focusing on the strengths and limitations.In addition,we review recent advancements in the identification of CEMP stars,emphasizing the growing role of machine learning in processing and analyzing the increasingly large data sets generated by modern astronomical surveys.Compared to traditional spectral analysis methods,machine learning offers greater efficiency in handling complex data,automatic extraction of stellar parameters,and improved prediction accuracy.Despite these advancements,the research faces persistent challenges,including the scarcity of labeled samples,limitations imposed by low-resolution spectra,and the lack of interpretability in machine learning models.To address these issues,the paper proposes potential solutions and future research directions aimed at advancing the study of CEMP stars and enhancing our understanding of their role in the chemical evolution of the universe.
基金partially supported by the National Natural Science Foundation of China 12173034 and 12322304he National Natural Science Foundation of Yunnan Province202301AV070002+1 种基金the Xingdian talent support program of Yunnan Provincethe science research grants from the China Manned Space Project with NO.CMS-CSST-2021-A09,CMS-CSST-2021-A08 and CMS-CSST-2021-B03。
文摘Accurate determinations of metallicity for large,complete stellar samples are essential for advancing various studies of the Milky Way.In this paper,we present a data-driven algorithm that leverages photometric data from the KiDS and the VIKING surveys to estimate stellar absolute magnitudes,effective temperatures,and metallicities.The algorithm is trained and validated using spectroscopic data from LAMOST,SEGUE,APOGEE,and GALAH,as well as a catalog of very metal-poor stars from the literature,and Gaia EDR3 data.This approach enables us to estimate metallicities,effective temperatures,and g-band absolute magnitudes for approximately 0.8 million stars in the KiDS data set.The photometric metallicity estimates exhibit an uncertainty of around 0.28 dex when compared to spectroscopic studies,within the metallicity range of−2 dex to 0.5 dex.The photometric effective temperature estimates have an uncertainty of around 149 K,while the uncertainty in the absolute magnitudes is approximately 0.36 mag.The metallicity estimates are reliable for values down to about−2 dex.This catalog represents a valuable resource for studying the structure and chemical properties of the Milky Way,offering an extensive data set for future investigations into Galactic formation and evolution.
基金partially supported by the National Natural Science Foundation of China(NSFC,Grant Nos.12173034 and 12322304)the National Natural Science Foundation of Yunnan Province 202301AV070002+1 种基金the Xingdian talent support program of Yunnan Provincethe science research grants from the China Manned Space Project with No.CMS-CSST-2021-A09,CMS-CSST-2021-A08 and CMS-CSST-2021-B03。
文摘Red clump(RC)stars are reliable standard candles for studying the structure and evolution of the Milky Way.In this study,we present empirical calibrations of RC absolute magnitudes in the Mephisto(v,g,r,i)and CSST(g,r,i)photometric systems using a high-purity sample of 25,059 RC stars cross-matched between APOGEE and Gaia DR3 XP spectra.Through synthetic photometry and polynomial fitting,we find that RC absolute magnitudes exhibit strong dependencies on effective temperature and metallicity,with the strongest variations observed in bluer bands and progressively decreasing towards redder wavelengths.In particular,the Mephisto v band exhibits the highest sensitivity,with variations reaching up to 2.0 mag across the metallicity range(−1.0 dex<[Fe/H]<0.5 dex)and the temperature range(4500–5200 K).The calibrations achieve high precision for all bands,enabling accurate determination of RC absolute magnitudes and distances.Furthermore,we evaluate the metallicity estimation capabilities of both systems using a Random Forest-based method,achieving a precision of 0.12 dex for Mephisto and 0.14 dex for CSST under typical photometric uncertainties(≤0.01 mag).These results provide robust tools for distance and metallicity determinations,supporting future Galactic structure studies with Mephisto and CSST data.
基金supported through HLM’s Program Penelitian Pengabdian Masyarakat ITB(P2MI)Astronomy Division,FMIPA ITB grant 2022-2023Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts。
文摘We present optical spectra of 10 Galactic Wolf-Rayet(WR)stars that consist of five WN and five WC stars.The optical observation was conducted using a low-resolution spectrograph NEO-R1000(λ/Δλ~1000)at GAO-ITB RTS(27.94 cm,F/10.0),Bosscha Observatory,Lembang.We implemented stellar atmosphere Postdam Wolf-Rayet(PoWR)grid modeling to derive stellar parameters.The normalized optical spectrum can be used to find the best model from the available PoWR grid,then we could derive stellar temperature and transformation radius.To derive luminosity,stellar radius and color excess,we conducted a Spectral Energy Distribution(SED)analysis with additional data on the near-ultraviolet spectrum from the International Ultraviolet Explorer(IUE)database,and UBV and 2MASS JHK broadband filter data.Additional analysis to derive asymptotic terminal wind velocity was conducted from the P-Cygni profile analysis of the high-resolution IUE ultraviolet spectrum.With previously derived parameters,we could determine the mass loss rate of the WR stars.Furthermore,we compared our results with previous work that used PoWR code and the differences are not more than 20%.We conclude that the PoWR spectral grid is sufficient to derive WR stellar parameters quickly and could provide more accurate initial parameter input to the PoWR program code.
基金supported by the National Natural Science Foundation of China(12273008,12025303,12403046)the National SKA Program of China(2022SKA0130104)+3 种基金the Natural Science and Technology Foundation of Guizhou Province(QiankehejichuMS[2025]266,[2023]024,ZK[2022]304)the Foundation of Guizhou Provincial Education Department(KY(2020)003)the Academic New Seedling Fund Project of Guizhou Normal University([2022]B18)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region(2022A03013-4).
文摘The emission of anomalous X-ray pulsars(AXPs)and soft gamma-ray repeaters(SGRs)is believed to be powered by the dissipation of their strong magnetic fields,which coined the name“magnetar”.By combining timing and energy observational results,the magnetar model can be easily appreciated.From a timing perspective,the magnetic field strengths of AXPs and SGRs,which are calculated under the assumption of dipole radiation,are extremely strong.From an energy perspective,the X-ray/soft gamma-ray luminosities of AXPs and SGRs are larger than their rotational energy loss rates(i.e.,L_(x>E_(rot)).It is thus reasonable to assume that the high-energy radiation comes from magnetic energy decay,and the magnetar model has been extensively discussed(or accepted).However,we argue that:(ⅰ)Calculating magnetic fields by assuming that rotational energy loss is dominated by dipole radiation(i.e.,E_(rot)■E_(μ))may be controversial,and we suggest that the energies carried by outflowing particles should also be considered.(ⅱ)The fact that X-ray luminosity is greater than the rotational energy loss rate does not necessarily mean that the emission energy comes from the magnetic field decaying,which requires further observational testing.Furthermore,some observational facts conflict with the“magnetar”model,such as observations of anti-magnetars,high magnetic field pulsars,and radio and X-ray observations of AXPs/SGRs.Therefore,we propose a crusted strange star model as an alternative,which can explain many more observational facts of AXPs/SGRs.
文摘We present a theoretical model for detecting axions from neutron stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair uu¯or dd¯, in loop(s) involving gluons. The chiral anomaly of QCD and the spontaneously broken symmetry are invoked to explain the non-conservation of the axion current. From the coupling form factors, the axion emissivities ϵacan be derived, from which fluxes can be determined. We predict a photon flux, which may be detectable by Fermi LAT, and limits on the QCD mass ma. In this model, axions decay to gamma rays in a 2-photon vertex. We may determine the expected fluxes from the theoretical emissivity. The sensitivity curve from the Fermi Large Area Telescope (Fermi LAT) would allow axion mass constraints for neutron stars as low as ma≤10−14eV 95% C.L. Axions could thus be detectable in gamma rays for neutron stars as distant as 100 kpc. A signal from LIGO GWS 170817 could be placed from the NS-NS merger, which gives an upper limit of ma≤10−10eV.
基金the Natural Science Foundation of Shandong Province with grant Nos.ZR2024MA063,ZR2022MA076 and ZR2022MA089Additional support was provided by the science research grants from the China Manned Space Project with grant Nos.CMS-CSST-2021-B05 and CMS-CSST-2021-A08+1 种基金supported by the National Natural Science Foundation of China(NSFC)under grant Nos.11873037 and 11803016Furthermore,the Young Scholars Program of Shandong University,Weihai(2016WHWLJH09)provided support for this research.
文摘Hot subdwarf stars are important celestial objects in the study of stellar physics,but the population remains limited.The LAMOST DR12-V1,released in 2025 March,is currently the world’s largest spectroscopic database,holding great potential for the search of hot subdwarf stars.In this study,we propose a two-stage deep learning model called the hot subdwarf network(HsdNet),which integrates multiple advanced techniques,comprising a binary classification model in stage one and a five-class classification model in stage two.HsdNet not only achieves high precision with 94.33%and 94.00%in the binary and the five-class classification stages,respectively,but also quantifies the predicted uncertainty,enhancing the interpretability of the classification results through visualizing the model’s key focus regions.We applied HsdNet to the 601,217 spectra from the LAMOST DR12-V1 database,conducting a two-stage search for hot subdwarf candidates.In stage one,we initially identified candidates using the binary classification model.In stage two,the five-class classification model was used to further refine these candidates.Finally,we confirmed 1008 newly identified hot subdwarf stars.The distribution of their atmospheric parameters is consistent with that of known hot subdwarf stars.These efforts are expected to significantly advance the research on hot subdwarf stars.
基金partially funded by the Horizontal Scientific Research Project of the National Astronomical Observatories of CAS(Grant No.E0900501)and the Theoretical Fundamental Research Special Project of the Changchun Observatory,National Astronomical Observatories,CAS(Grant No.Y990000205)。
文摘Research on the properties of neutron stars with dark energy is a particularly interesting yet unresolved problem in astrophysics.We analyze the influence of dark energy on the equation of state,the maximum mass,the surface gravitational redshift and the Keplerian frequency for the traditional neutron star and the hyperon star matter within the relativistic mean field theory,using the GM1 and TM1 parameter sets by considering the two flavor symmetries of SU(6)and SU(3)combined with the observations of PSR J1614-2230,PSR J0348+0432,PSR J0030+0451,RX J0720.4-3125,and 1E 1207.4-5209.It is found that the existence of dark energy leads to the softened equations of the state of the traditional neutron star and the hyperon star.The radius of a fixed-mass traditional neutron star(or hyperon star)with dark energy becomes smaller,which leads to increased compactness.The existence of dark energy can also enhance the surface gravitational redshift and the Keplerian frequency of traditional neutron stars and hyperon stars.The growth of the Keplerian frequency may cause the spin rate to speed up,which may provide a possible way to understand and explain the pulsar glitch phenomenon.Specifically,we infer that the mass and the surface gravitational redshift of PSR J1748-2446ad without dark energy for the GM1(TM1)parameter set are 1.141 M_(☉)(1.309 M_(☉))and 0.095(0.105),respectively.The corresponding values for the GM1(TM1)parameter set are 0.901 M_(☉)(1.072M_(☉))and 0.079(0.091)if PSR J1748-2446ad contains dark energy withα=0.05.PSR J1748-2446ad may be a low-mass pulsar with a lower surface gravitational redshift under our selected models.
基金supported by the Ministry of Science and Education,FEUZ-2020-0038。
文摘The spinning-up of the accreting component in the process of conservative mass exchange is considered in binary systems—progenitors of systems consisting of a main sequence Be-star and an O-subdwarf.During the mass exchange,the meridional circulation transfers 80%-85%of the angular momentum that entered the accretor together with the accreted matter to the accretor surface.This angular momentum is removed from the accretor by the disk.When the mass exchange finishes,the accretor has a rotation typical of classical Be-type stars.
文摘With the advancement of astronomical observation technology,people have a deeper understanding of the formation and evolution of galaxies,but many details of our own Milky Way and other external galaxies are still unknown.Therefore,by studying the formation and orbital transformation mechanism of satellites,planets and stars,the author puts forward a new theory on the formation and evolution of stars and galaxies,thus revealing the hierarchical structure of galaxies and the formation and evolution laws of main sequence stars,red giants,white dwarfs,black dwarfs,supernovae,neutron stars,black holes and quasars.Some special phenomena in the course of star formation and evolution,such as sunspots,flares,fast radio bursts and gamma-ray bursts,have also been revealed.
文摘In the present article,we introduce a completely new regular model for static,spherically symmetric celestial fluid spheres in embedding classⅠspacetime.In this regard,needfully,we propose a new suitable metric potential e^(λ(r))to generate the present model.The various analyses on energy density,pressure,anisotropic factor,mass,compactness parameter,redshift,and energy condition make sure the model is physically viable on the ground of model stars Vela X-1,Cen X-3,SMC X-4,and LMC X-4.The reported solutions also respect the equilibrium state by satisfying the Tolman-Oppenheimer-Volkoff(TOV)equation and ensure stability by satisfying the causality condition,condition on the adiabatic index,and Harrison-Zeldovich-Novikov condition.The generated M-R graph matches the ranges of masses and radii for the model compact stars.Additionally,this study provides estimates of the moment of inertia based on the I-M graph.
基金supported by the National SKA Program of China(2020SKA0120100)supported by NSFC grant No.12203017。
文摘Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate.Enormous energy is surely needed to understand various observations,such asγ-ray bursts,fast radio bursts and softγ-ray repeaters.In this paper,the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars,with two anisotropic models to calculate in general relativity.It is found that huge free energy(>10^(46)erg)could be released via starquakes,given an extremely small anisotropy((p_(t)-p_(r))/p_(r)~10^(-4),with pt/pr the tangential/radial pressure),implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.
