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
For k given graphs H_(1),...,H_(k) with k≥2,the k-color Ramsey number R(H_(1),...,H_(k)) represents the minimum integer N with the following property:if the edges of the complete graph K_(N) are colored with k colors...For k given graphs H_(1),...,H_(k) with k≥2,the k-color Ramsey number R(H_(1),...,H_(k)) represents the minimum integer N with the following property:if the edges of the complete graph K_(N) are colored with k colors,then there exists some i with 1≤i≤k such that K_(N) has a subgraph in color i isomorphic to H_(i).Let C_(m) be a cycle of length m and K_(1,n) a star of order n+1.In this paper,we systematically introduce the latest research progress on star-quadrilateral Ramsey numbers and provide an overview of Ramsey numbers concerning quadrilaterals,including multicolor cases.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
Daytime star images captured by dedicated near-space star sensors are characterized by short exposures,high noise,and low Signal-to-Noise Ratios(SNRs).Such imaging is also affected by atmospheric turbulence,causing op...Daytime star images captured by dedicated near-space star sensors are characterized by short exposures,high noise,and low Signal-to-Noise Ratios(SNRs).Such imaging is also affected by atmospheric turbulence,causing optical phenomena,such as scintillation,distortion,and jitter.This causes difficulty in recording high-precision star images during the daytime.This study proposes an adaptive star point extraction method based on dynamically predicting stars'positions.First,it predicts the approximate position of stars based on the star catalog,sensor attitude,observation time,and other information,improving the extraction accuracy.Second,it employs a regional SNR sorting method that adaptively selects star images with higher SNRs,suppressing the scintillation effect and enhancing the SNR of star images.Third,depending on the star's motion trajectory characteristics on the image plane,it utilizes the centroid smoothing method for extraction,thus overcoming the impact of star drift.Field experiments demonstrate that the proposed method can effectively overcome star scintillation,drift,and irregular imaging caused by atmospheric turbulence,achieving a 100%success rate.Moreover,the extraction accuracy improves by more than 80%compared to traditional adaptive methods,attaining a value of 0.05 pixels(0.5"),thereby meeting the requirements of daytime astronomical attitude determination and positioning.展开更多
In order to solve the problem that the star point positioning accuracy of the star sensor in near space is decreased due to atmospheric background stray light and rapid maneuvering of platform, this paper proposes a s...In order to solve the problem that the star point positioning accuracy of the star sensor in near space is decreased due to atmospheric background stray light and rapid maneuvering of platform, this paper proposes a star point positioning algorithm based on the capsule network whose input and output are both vectors. First, a PCTL (Probability-Coordinate Transformation Layer) is designed to represent the mapping relationship between the probability output of the capsule network and the star point sub-pixel coordinates. Then, Coordconv Layer is introduced to implement explicit encoding of space information and the probability is used as the centroid weight to achieve the conversion between probability and star point sub-pixel coordinates, which improves the network’s ability to perceive star point positions. Finally, based on the dynamic imaging principle of star sensors and the characteristics of near-space environment, a star map dataset for algorithm training and testing is constructed. The simulation results show that the proposed algorithm reduces the MAE (Mean Absolute Error) and RMSE (Root Mean Square Error) of the star point positioning by 36.1% and 41.7% respectively compared with the traditional algorithm. The research results can provide important theory and technical support for the scheme design, index demonstration, test and evaluation of large dynamic star sensors in near space.展开更多
Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects ...Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects the intrinsic composition of the gas cloud present at its birth. Using an abundance decomposition method, we fit25 elements from the abundance data set, including 10 heavy neutron-capture elements. We explore the astrophysical origin of the elements in this star through its abundance ratios and component ratios. We find that the contributions from the massive stars played a significant role in the production of light elements in the program star. Our analysis reveals that the heavy neutron-capture elements are produced purely by the main r-process. However, the adopted main r-process model does not adequately fit the observed data, suggesting another main r-process pattern may exist.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
We identify a point-symmetric morphology of three pairs of ears/clumps in the core-collapse supernova remnant(CCSNR)Puppis A,supporting the jittering jets explosion mechanism(JJEM).In the JJEM,the three pairs of jets ...We identify a point-symmetric morphology of three pairs of ears/clumps in the core-collapse supernova remnant(CCSNR)Puppis A,supporting the jittering jets explosion mechanism(JJEM).In the JJEM,the three pairs of jets that shaped the three pairs of ears/clumps in Puppis A are part of a large set,about 10–30 pairs of jets,that exploded Puppis A.Some similarities in morphological features between CCSNR Puppis A and three multipolar planetary nebulae considered to have been shaped by jets solidify the claim for shaping by jets.Puppis A has a prominent dipole structure,where one side is bright with a well-defined boundary,while the other is faint and defused.The neutron star(NS)has a natal kick velocity in the opposite direction to the denser part of the dipole structure.We propose a new mechanism in the frame of the JJEM that imparts a natal kick to the NS,the kick-byearly asymmetrical pair(kick-BEAP)mechanism.At the early phase of the explosion process,the NS launches a pair of jets where one jet is much more energetic than the counter jet.The more energetic jet compresses a dense side to the CCSNR,and,by momentum conservation,the NS recoils in the opposite direction.Our study supports the JJEM as the primary explosion mechanism of core-collapse supernovae and enriches this explosion mechanism by introducing the novel kick-BEAP mechanism.展开更多
This paper yields a new exact solution for dense stellar objects by employing the Einstein-Maxwell system of differential equations.The established model comprises three interior layers with distinguishable equations ...This paper yields a new exact solution for dense stellar objects by employing the Einstein-Maxwell system of differential equations.The established model comprises three interior layers with distinguishable equations of state(EoSs):the polytropic EoS at the core layer,the quadratic EoS at the intermediate layer and the modified Van der Waals EoS at the envelope layer.The physical features indicate that the matter variables,metric functions and other physical conditions are viable with dense astrophysical objects.Excitingly,this model is an extension solution of the two-layered model generated by Sunzu and Lighuda.The layers are matched gently across the junctions with the care of the Reissner-Nordström exterior spacetime.Utilizing our model,star masses and radii compatible with observations and satisfactorily known objects are generated.The findings from this paper may be useful to describes purported strange stars such as SAX J1808.4-3658 and binary stars such as Vela X-1.展开更多
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
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
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
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.
基金supported by NSFC(Nos.12161141003,11931006)supported by NSFC(Nos.11801520,12171436,12271489)supported by NSFC(No.11601527)。
文摘For k given graphs H_(1),...,H_(k) with k≥2,the k-color Ramsey number R(H_(1),...,H_(k)) represents the minimum integer N with the following property:if the edges of the complete graph K_(N) are colored with k colors,then there exists some i with 1≤i≤k such that K_(N) has a subgraph in color i isomorphic to H_(i).Let C_(m) be a cycle of length m and K_(1,n) a star of order n+1.In this paper,we systematically introduce the latest research progress on star-quadrilateral Ramsey numbers and provide an overview of Ramsey numbers concerning quadrilaterals,including multicolor cases.
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.
基金funded by the National Natural Science Foundation of China(Nos.42374011,42074013)through the Natural Science Foundation’s Outstanding Youth Fund Program of Henan Province,China(Nos.242300421150,242300421151)。
文摘Daytime star images captured by dedicated near-space star sensors are characterized by short exposures,high noise,and low Signal-to-Noise Ratios(SNRs).Such imaging is also affected by atmospheric turbulence,causing optical phenomena,such as scintillation,distortion,and jitter.This causes difficulty in recording high-precision star images during the daytime.This study proposes an adaptive star point extraction method based on dynamically predicting stars'positions.First,it predicts the approximate position of stars based on the star catalog,sensor attitude,observation time,and other information,improving the extraction accuracy.Second,it employs a regional SNR sorting method that adaptively selects star images with higher SNRs,suppressing the scintillation effect and enhancing the SNR of star images.Third,depending on the star's motion trajectory characteristics on the image plane,it utilizes the centroid smoothing method for extraction,thus overcoming the impact of star drift.Field experiments demonstrate that the proposed method can effectively overcome star scintillation,drift,and irregular imaging caused by atmospheric turbulence,achieving a 100%success rate.Moreover,the extraction accuracy improves by more than 80%compared to traditional adaptive methods,attaining a value of 0.05 pixels(0.5"),thereby meeting the requirements of daytime astronomical attitude determination and positioning.
文摘In order to solve the problem that the star point positioning accuracy of the star sensor in near space is decreased due to atmospheric background stray light and rapid maneuvering of platform, this paper proposes a star point positioning algorithm based on the capsule network whose input and output are both vectors. First, a PCTL (Probability-Coordinate Transformation Layer) is designed to represent the mapping relationship between the probability output of the capsule network and the star point sub-pixel coordinates. Then, Coordconv Layer is introduced to implement explicit encoding of space information and the probability is used as the centroid weight to achieve the conversion between probability and star point sub-pixel coordinates, which improves the network’s ability to perceive star point positions. Finally, based on the dynamic imaging principle of star sensors and the characteristics of near-space environment, a star map dataset for algorithm training and testing is constructed. The simulation results show that the proposed algorithm reduces the MAE (Mean Absolute Error) and RMSE (Root Mean Square Error) of the star point positioning by 36.1% and 41.7% respectively compared with the traditional algorithm. The research results can provide important theory and technical support for the scheme design, index demonstration, test and evaluation of large dynamic star sensors in near space.
基金supported by the National Key Basic R&D Program of China No. 2024YFA1611903the National Natural Science Foundation of China (NSFC, Grant No. 12173013)+2 种基金the project of Hebei provincial department of science and technology under the grant No. 226Z7604Gthe Hebei NSF (No. A2021205006)the China Manned Space Project for funding support of this study
文摘Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects the intrinsic composition of the gas cloud present at its birth. Using an abundance decomposition method, we fit25 elements from the abundance data set, including 10 heavy neutron-capture elements. We explore the astrophysical origin of the elements in this star through its abundance ratios and component ratios. We find that the contributions from the massive stars played a significant role in the production of light elements in the program star. Our analysis reveals that the heavy neutron-capture elements are produced purely by the main r-process. However, the adopted main r-process model does not adequately fit the observed data, suggesting another main r-process pattern may exist.
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A grant from the Pazy Foundation supported this research。
文摘We identify a point-symmetric morphology of three pairs of ears/clumps in the core-collapse supernova remnant(CCSNR)Puppis A,supporting the jittering jets explosion mechanism(JJEM).In the JJEM,the three pairs of jets that shaped the three pairs of ears/clumps in Puppis A are part of a large set,about 10–30 pairs of jets,that exploded Puppis A.Some similarities in morphological features between CCSNR Puppis A and three multipolar planetary nebulae considered to have been shaped by jets solidify the claim for shaping by jets.Puppis A has a prominent dipole structure,where one side is bright with a well-defined boundary,while the other is faint and defused.The neutron star(NS)has a natal kick velocity in the opposite direction to the denser part of the dipole structure.We propose a new mechanism in the frame of the JJEM that imparts a natal kick to the NS,the kick-byearly asymmetrical pair(kick-BEAP)mechanism.At the early phase of the explosion process,the NS launches a pair of jets where one jet is much more energetic than the counter jet.The more energetic jet compresses a dense side to the CCSNR,and,by momentum conservation,the NS recoils in the opposite direction.Our study supports the JJEM as the primary explosion mechanism of core-collapse supernovae and enriches this explosion mechanism by introducing the novel kick-BEAP mechanism.
文摘This paper yields a new exact solution for dense stellar objects by employing the Einstein-Maxwell system of differential equations.The established model comprises three interior layers with distinguishable equations of state(EoSs):the polytropic EoS at the core layer,the quadratic EoS at the intermediate layer and the modified Van der Waals EoS at the envelope layer.The physical features indicate that the matter variables,metric functions and other physical conditions are viable with dense astrophysical objects.Excitingly,this model is an extension solution of the two-layered model generated by Sunzu and Lighuda.The layers are matched gently across the junctions with the care of the Reissner-Nordström exterior spacetime.Utilizing our model,star masses and radii compatible with observations and satisfactorily known objects are generated.The findings from this paper may be useful to describes purported strange stars such as SAX J1808.4-3658 and binary stars such as Vela X-1.
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.
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.
