White dwarfs(WDs)are the final stage for most low and intermediate mass stars,which play an important role in understanding stellar evolution and galactic history.Here we performed an asteroseismological analysis on T...White dwarfs(WDs)are the final stage for most low and intermediate mass stars,which play an important role in understanding stellar evolution and galactic history.Here we performed an asteroseismological analysis on TIC 231277791 based on 10 independent modes reported by Romero et al.Two groups of modes were identified with frequency splitting:mode identification_1 with one l=1,m=0 mode,two l=2,m=0 modes,and three l=1 or 2,m=0 modes,and mode identification_2 with one l=1,m=0 mode,three l=2,m=0 modes,and one l=1 or 2,m=0 mode.The rotation period is derived to be 41.64±2.73 hr for TIC 231277791.We established a large sample(7,558,272)of DAV star models using the White Dwarf Evolution Code(WDEC;2018,v16),resulting of optimal models with model_1(mode identification_1):M_(*)=0.570±0.005 M⊙,Teff=11300±10 K,-log(MH/M_(*))=9.15±0.01,-log(M_(He)/M_(*))=4.94±0.01,andσrms=0.06 s,and model_2(mode identification_2):M_(*)=0.720±0.005 M⊙,Teff=1910±10 K,-log(M_(H)/M_(*))=6.11±0.01,-log(M_(He)/M_(*))=3.09±0.01,andσrms=0.04 s.The central oxygen abundances are 0.71(optimal model_1)and 0.72(optimal model_2),respectively,which are consistent with the results of stellar structure and evolution theory.展开更多
Element diffusion has small but significant effects on the structure of the stellar interior.It is interesting to investigate the effects of element diffusion using asteroseismology.We have constructed two grids of st...Element diffusion has small but significant effects on the structure of the stellar interior.It is interesting to investigate the effects of element diffusion using asteroseismology.We have constructed two grids of stellar models,one with diffusion and one without,for solar-like stars with masses between 0.9 and 1.4 solar masses,and varied initial helium abundance and metallicity.The oscillation frequencies of all stellar models have also been calculated.Piecewise Hermite cubic polynomials are adopted to interpolate stellar p-mode frequencies at an arbitrary age on a stellar evolutionary track.We have investigated 16 Kepler solar-like stars by comparing the model frequencies with observations.The suggested ranges of stellar parameters and some global variables are obtained.For all stars,the best model reproduces the observational frequencies with aχ^(2)of the order of unity.It has been found that element diffusion is important in modeling solar-like stars.Without diffusion,the best value of the initial helium abundance is below the primordial helium abundance from Big Bang nucleosynthesis.When diffusion is taken into account,the required initial helium abundance increases to be higher than the primordial abundance.Diffusion also generally improves the frequency fitting results by reducing the minimum ofχ^(2).Investigation of the second difference of the oscillation frequencies on KIC 8694723 and KIC 10454113 indicates that the current model of element diffusion may underestimate the strength of settling.展开更多
Asteroseismic observations are crucial to constrain stellar models with precision.Bayesian Estimation of STellar Parameters(BESTP)is a tool that utilizes Bayesian statistics and nested sampling Monte Carlo algorithm t...Asteroseismic observations are crucial to constrain stellar models with precision.Bayesian Estimation of STellar Parameters(BESTP)is a tool that utilizes Bayesian statistics and nested sampling Monte Carlo algorithm to search for the stellar models that best match a given set of classical and asteroseismic constraints from observations.The computation and evaluation of models are efficiently performed in an automated and multi-threaded way.To illustrate the capabilities of BESTP,we estimate fundamental stellar properties for the Sun and the red-giant star HD 222076.In both cases,we find models that are consistent with observations.We also evaluate the improvement in the precision of stellar parameters when the oscillation frequencies of individual modes are included as constraints,compared to the case when only the large frequency separation is included.For the solar case,the uncertainties of estimated masses,radii and ages are reduced by 0.7%,0.3%and 8%respectively.For HD 222076,they are reduced even more noticeably by 2%,0.5%and 4.7%respectively.We also note an improvement of 10%for the age of HD 222076 when the Gaia parallax is included as a constraint compared to the case when only the large separation is included as a constraint.展开更多
Lithium is an ancient element that was first produced by the Big Bang Nucleosynthesis(BBN)a few minutes after the birth of the Universe.Lithium is a sensitive tracer for a number of processes in a variety of astrophys...Lithium is an ancient element that was first produced by the Big Bang Nucleosynthesis(BBN)a few minutes after the birth of the Universe.Lithium is a sensitive tracer for a number of processes in a variety of astrophysical environments due to its multi-channels of production and fragility.These features also make lithium a complex element at the center of many unsolved problems.The behavior of lithium in the low-mass evolved stars is one such issue.It is known that such stars not only destroy but also produce lithium,while neither the destruction details nor the production mechanisms over different evolutionary phases are clear.In this paper,we summarize the recent results obtained from the studies combining large-scale spectroscopic surveys,asteroseismology,and traditional high-resolution spectroscopy.We present the detailed evolution behaviors from the red giant branch(RGB)to the red clump(RC)phase characterized by the core helium-burning in the stellar interior.We show the new signatures discovered from the recent studies for the lithium-enhanced giants and also discuss various observational and theoretical constraints on lithium production in red clump stars.展开更多
Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected ...Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO star sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars by combining asteroseismic parameters deduced from Kepler photometry and atmospheric parameters deduced from LAMOST spectra. With this sample, we examine the age determination as well as the contamination rate of the MSTO star sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr （7%） and a dispersion of 2.71 Gyr （28%）. The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.展开更多
基金supported by the International Centre of Supernovae,Yunnan Key Laboratory(No.202302AN36000101)supported by the Yunnan Province Youth Talent Project(2019-182)。
文摘White dwarfs(WDs)are the final stage for most low and intermediate mass stars,which play an important role in understanding stellar evolution and galactic history.Here we performed an asteroseismological analysis on TIC 231277791 based on 10 independent modes reported by Romero et al.Two groups of modes were identified with frequency splitting:mode identification_1 with one l=1,m=0 mode,two l=2,m=0 modes,and three l=1 or 2,m=0 modes,and mode identification_2 with one l=1,m=0 mode,three l=2,m=0 modes,and one l=1 or 2,m=0 mode.The rotation period is derived to be 41.64±2.73 hr for TIC 231277791.We established a large sample(7,558,272)of DAV star models using the White Dwarf Evolution Code(WDEC;2018,v16),resulting of optimal models with model_1(mode identification_1):M_(*)=0.570±0.005 M⊙,Teff=11300±10 K,-log(MH/M_(*))=9.15±0.01,-log(M_(He)/M_(*))=4.94±0.01,andσrms=0.06 s,and model_2(mode identification_2):M_(*)=0.720±0.005 M⊙,Teff=1910±10 K,-log(M_(H)/M_(*))=6.11±0.01,-log(M_(He)/M_(*))=3.09±0.01,andσrms=0.04 s.The central oxygen abundances are 0.71(optimal model_1)and 0.72(optimal model_2),respectively,which are consistent with the results of stellar structure and evolution theory.
基金Funding for Yunnan Observatories is co-sponsored by the National Key R&D Program of China(Grant No.2021YFA1600400/2021YFA1600402)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB 41000000)+3 种基金the National Natural Science Foundation of China(Grant Nos.1177064 and 12133011)the Foundation of the Chinese Academy of Sciences(Light of West China Program and Youth Innovation Promotion Association)the Yunnan Ten Thousand Talents Plan Young and Elite Talents ProjectInternational Centre of Supernovae,Yunnan Key Laboratory(No.202302AN360001)。
文摘Element diffusion has small but significant effects on the structure of the stellar interior.It is interesting to investigate the effects of element diffusion using asteroseismology.We have constructed two grids of stellar models,one with diffusion and one without,for solar-like stars with masses between 0.9 and 1.4 solar masses,and varied initial helium abundance and metallicity.The oscillation frequencies of all stellar models have also been calculated.Piecewise Hermite cubic polynomials are adopted to interpolate stellar p-mode frequencies at an arbitrary age on a stellar evolutionary track.We have investigated 16 Kepler solar-like stars by comparing the model frequencies with observations.The suggested ranges of stellar parameters and some global variables are obtained.For all stars,the best model reproduces the observational frequencies with aχ^(2)of the order of unity.It has been found that element diffusion is important in modeling solar-like stars.Without diffusion,the best value of the initial helium abundance is below the primordial helium abundance from Big Bang nucleosynthesis.When diffusion is taken into account,the required initial helium abundance increases to be higher than the primordial abundance.Diffusion also generally improves the frequency fitting results by reducing the minimum ofχ^(2).Investigation of the second difference of the oscillation frequencies on KIC 8694723 and KIC 10454113 indicates that the current model of element diffusion may underestimate the strength of settling.
基金funded by the Fundamental Research Funds for the Central Universities(Grant 19lgpy278)supported by a grant from the Max Planck Society to prepare for the scientific exploitation of the PLATO mission。
文摘Asteroseismic observations are crucial to constrain stellar models with precision.Bayesian Estimation of STellar Parameters(BESTP)is a tool that utilizes Bayesian statistics and nested sampling Monte Carlo algorithm to search for the stellar models that best match a given set of classical and asteroseismic constraints from observations.The computation and evaluation of models are efficiently performed in an automated and multi-threaded way.To illustrate the capabilities of BESTP,we estimate fundamental stellar properties for the Sun and the red-giant star HD 222076.In both cases,we find models that are consistent with observations.We also evaluate the improvement in the precision of stellar parameters when the oscillation frequencies of individual modes are included as constraints,compared to the case when only the large frequency separation is included.For the solar case,the uncertainties of estimated masses,radii and ages are reduced by 0.7%,0.3%and 8%respectively.For HD 222076,they are reduced even more noticeably by 2%,0.5%and 4.7%respectively.We also note an improvement of 10%for the age of HD 222076 when the Gaia parallax is included as a constraint compared to the case when only the large separation is included as a constraint.
基金This work is supported by the National Natural Science Foundation of China(11988101,12090040,12090044,12022304,11833006,11973052,11973049,11890694,and U2031203)the National Key R&D Program of China(2019YFA0405502)+6 种基金support of the JSPS-CAS Joint Research Program.H.-L.Y.and H.L.acknowledge support from the Youth Innovation Promotion Association of the CAS(id.2019060 and Y202017,respectively)NAOC Nebula Talents Program.J.-H.Z.acknowledges support from NSFC(12103063)from China Postdoctoral Science Foundation funded project(2020M680672)Y.B.K acknowledges the support of the NSFC(11850410437)H.L.acknowledges support from the Strategic Priority Research Program of Chinese Academy of Sciences,(XDB34020205)Guoshoujing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST)is a National Major Scientific Project built by the Chinese Academy of Sciences.Funding for the project has been provided by the National Development and Reform CommissionLAMOST is operated and managed by the National Astronomical Observatories,Chinese Academy of Sciences.
文摘Lithium is an ancient element that was first produced by the Big Bang Nucleosynthesis(BBN)a few minutes after the birth of the Universe.Lithium is a sensitive tracer for a number of processes in a variety of astrophysical environments due to its multi-channels of production and fragility.These features also make lithium a complex element at the center of many unsolved problems.The behavior of lithium in the low-mass evolved stars is one such issue.It is known that such stars not only destroy but also produce lithium,while neither the destruction details nor the production mechanisms over different evolutionary phases are clear.In this paper,we summarize the recent results obtained from the studies combining large-scale spectroscopic surveys,asteroseismology,and traditional high-resolution spectroscopy.We present the detailed evolution behaviors from the red giant branch(RGB)to the red clump(RC)phase characterized by the core helium-burning in the stellar interior.We show the new signatures discovered from the recent studies for the lithium-enhanced giants and also discuss various observational and theoretical constraints on lithium production in red clump stars.
基金The Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission+4 种基金National Astronomical Observatories, Chinese Academy of Sciencessupported by grants 11273007 and 10933002 from the National Natural Science Foundation of Chinathe Joint Research Fund in Astronomy (U1631236) under cooperative agreement between the National Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS)the Fundamental Research Funds for the Central UniversitiesYouth Scholars Program of Beijing Normal University
文摘Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO star sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars by combining asteroseismic parameters deduced from Kepler photometry and atmospheric parameters deduced from LAMOST spectra. With this sample, we examine the age determination as well as the contamination rate of the MSTO star sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr （7%） and a dispersion of 2.71 Gyr （28%）. The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.
