The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function ...The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function of the properties of the host star, we must accurately determine the parameters of the EH stars first. For this rea- son, we constructed a grid of stellar models including diffusion and rotation-induced extra-mixing with given ranges of input parameters （i.e. mass, metallicity and initial rotation rate）. In addition to the commonly used observational constraints such as the effective temperature Tell, luminosity L and metallicity [Fe/H], we added two obser- vational constraints, the lithium abundance log N （Li） and the rotational period Prot. These two additional observed parameters can set further constraints on the model due to their correlations with mass, age and other stellar properties. Hence, our estimations of the fundamental parameters for these EH stars and their planets have a higher preci- sion than previous works. Therefore, the combination of rotational period and lithium helps us to obtain more accurate parameters for stars, leading to an improvement in knowledge about the physical state of EH stars and their planets.展开更多
We collected almost all Highly Processed Data Products （HPDP） of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae （PPNs）.Tho...We collected almost all Highly Processed Data Products （HPDP） of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae （PPNs）.Those infrared spectra are primarily analyzed and discussed.It is shown that either spectral shapes/peaks,or main molecular/dust features are evidenced to change in the sequence of visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich PPNs.Statistically,in this sequence,continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths.In addition,in this sequence,intensities of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths.Furthermore,from 2MASS and IRAS photometric data,the sequence is also proved.Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy,that is the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars → carbon-rich PPNs.展开更多
We present an updated catalog of 46,753 radial velocity(RV)standard stars selected from the APOGEE DR17.These stars cover the Northern and Southern Hemispheres almost evenly,with 62%being red giants and 38%being main ...We present an updated catalog of 46,753 radial velocity(RV)standard stars selected from the APOGEE DR17.These stars cover the Northern and Southern Hemispheres almost evenly,with 62%being red giants and 38%being main sequence stars.These RV standard stars are stable on a baseline longer than 200 days(with 54%longer than one year and 10%longer than five years)with a median stability better than 215 m s~(-1).The average number of observations of those stars is 5 and each observation is required to have signal-to-noise ratio greater than50 and RV measurement error smaller than 500 m s~(-1).Based on the new APOGEE RV standard star catalog,we have checked the RV zero-points(RVZPs)for current large-scale stellar spectroscopic surveys including RAVE,LAMOST,GALAH and Gaia.By careful analysis,we estimate their mean RVZP to be+0.149 kms~(-1),+4.574 km s~(-1)(for LRS),-0.031 km s~(-1)and+0.014 kms~(-1),respectively,for the four surveys.In the RAVE,LAMOST(for MRS),GALAH and Gaia surveys,RVZP exhibits a systematic trend with stellar parameters(mainly[Fe/H],T_(eff),log g,G_(BP)-G_(RP)and G_(RVS)).The corrections to those small but clear RVZPs are of vital importance for these massive spectroscopic surveys in various studies that require extremely high RV accuracies.展开更多
The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identif...The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum （LRS） database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10μm and/or 18 μm. These newly identified stars are located in the Regions Ilia and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.展开更多
We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Ga...We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.展开更多
In the Wide-field Infrared Survey Explorer （WISE） all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near...In the Wide-field Infrared Survey Explorer （WISE） all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near-IR source within 3. We search for their identifications in the SIMBAD database and find 3.2 million identified sources. Based on these known sources, we establish three criteria for selecting candidate asymptotic giant branch （AGB） stars in the Galaxy, which are three defined zones in a color-color diagram, Galactic latitude ｜b｜ 〈 20°, and ＂corrected＂ WISE third-band W3c≤ 11. Applying these criteria to the WISE＋2MASS sources, 1.37 million of them are selected. We analyze the WISE third-band W3 distribution of the selected sources, and further establish that W3〈8 is required in order to exclude a large fraction of normal stars from them. We therefore find 0.47 million candidate AGB stars in our Galaxy from the WISE source catalog. Using W3c, we estimate their distances and derive their Galactic distributions. The candidates are generally distributed around the Galactic center uniformly, with 68% （1-σ） of them within approximately 8 kpc. We discuss the idea that optical spectroscopy can be used to verify the C-rich AGB stars in our candidates, and thus a fraction of them （-10%） will be good targets for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） survey that is planned to start in fall of 2012.展开更多
We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612 MHz OH...We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612 MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygen- rich stars must be done with caution, because, in general, it has only a statistical meaning.展开更多
In this work, we select spectra of stars with high signal-to-noise ratio from LAMOST data and map their MK classes to the spectral features. The equivalent widths of prominent spectral lines, which play a similar role...In this work, we select spectra of stars with high signal-to-noise ratio from LAMOST data and map their MK classes to the spectral features. The equivalent widths of prominent spectral lines, which play a similar role as multi-color photometry, form a clean stellar locus well ordered by MK classes. The advantage of the stellar locus in line indices is that it gives a natural and continuous classification of stars consistent with either broadly used MK classes or stellar astrophysical parameters. We also employ an SVM-based classification algorithm to assign MK classes to LAMOST stellar spectra. We find that the completenesses of the classifications are up to 90% for A and G type stars, but they are down to about 50% for OB and K type stars. About 40% of the OB and K type stars are mis-classified as A and G type stars,respectively. This is likely due to the difference in the spectral features between late B type and early A type stars or between late G and early K type stars being very weak. The relatively poor performance of the automatic MK classification with SVM suggests that the direct use of line indices to classify stars is likely a more preferable choice.展开更多
Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type （temperatures T1 = T2 = 6100 K）. NSVS 2569022 undergoes a total e...Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type （temperatures T1 = T2 = 6100 K）. NSVS 2569022 undergoes a total eclipse of W subtype and the mass ratio is well-determined. Its extremely small value of only 0.077 implies that the target will probably experience instability and a possible merger. This value ranks NSVS 2569022 in sixth place among binaries with the smallest mass ratio. Based on an empirical relation of ＂period - total mass＂ for low mass-ratio binaries, we estimate the global parameters of NSVS 2569022： masses M1 = 1.17 M⊙ and M2 = 0.09 M⊙; radii R1 = 1.19 R⊙ and R2 = 0.38 R⊙; luminosities L1 = 1.73 L⊙ and L2 = 0.17L⊙. An analysis of the characteristics of binaries with extremely low-mass ratios is made. NSVS 2569022 turns out to be a peculiar binary among W UMa stars with extremely small mass ratios due to its unexpectedly small fill-out factor of only 0.014 （slightly overcontact configuration）.展开更多
We present LAMOST data on 168 γ Doradus(γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period(P), temperature(T), gra...We present LAMOST data on 168 γ Doradus(γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period(P), temperature(T), gravitational acceleration(log(g)) and metallicity [Fe/H] are shown. It is found that most γ Dor variables are main-sequence stars with early F spectral types and temperatures from 6880 K to7280 K. They are slightly more metal poor than the Sun with a metallicity range from-0.4 to 0. On the H-R and log g-T diagrams, both the γ Dor and δ Scuti(δ Sct) stars occupy in the same region and some are beyond the borders predicted by current stellar pulsation theories. It is discovered that the physical properties of γ Dor stars are similar to those of long-period δ Sct(P > 0.3 d) stars. The stellar atmospheric parameters are all correlated with the pulsation period for short-period δ Sct variables(P < 0.3 d), but there are no such relations for γ Dor or long-period δ Sct stars. These results reveal that γ Dor and long-period δ Sct are the same group of pulsating stars and they are different from short-period δ Sct variables. Meanwhile, 33γ Dor stars are identified as candidates of binary or multiple systems.展开更多
Asteroseismology allows for deriving precise values of the surface gravity of stars. The accurate asteroseismic determinations now available for the large number of stars in the Kepler fields can be used to check and ...Asteroseismology allows for deriving precise values of the surface gravity of stars. The accurate asteroseismic determinations now available for the large number of stars in the Kepler fields can be used to check and calibrate surface gravities that are currently being obtained spectroscopically for a huge number of stars targeted by large-scale spectroscopic surveys, such as the on-going Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） Galactic survey. The LAMOST spectral surveys have obtained a large number of stellar spectra in the Kepler fields. Stellar atmospheric parameters of those stars have been determined with the LAMOST Stellar Parameter Pipeline at Peking University （LSP3）, by template matching with the MILES empirical spectral library. In the current work, we compare surface gravities yielded by LSP3 with those of two asteroseismic samples-- the largest Kepler asteroseismic sample and the most accurate Kepler asteroseismic sample. We find that LSP3 surface gravities are in good agreement with asteroseismic values of Hekker et al., with a dispersion of -0.2 dex. Except for a few cases, asteroseismic surface gravities ofHuber et al. and LSP3 spectroscopic values agree for a wide range of surface gravities. However, some patterns in the differences can be identified upon close inspection. Potential ways to further improve the LSP3 spectroscopic estimation of stellar atmospheric parameters in the near future are briefly discussed. The effects of effective temperature and metallicity on asteroseismic determinations of surface gravities for giant stars are also discussed.展开更多
Using stellar evolutionary models, we investigate the effects of convective overshooting on naked helium stars. We find that a larger value of overshooting parameter δov results in a larger convective core, which pro...Using stellar evolutionary models, we investigate the effects of convective overshooting on naked helium stars. We find that a larger value of overshooting parameter δov results in a larger convective core, which prolongs the lifetimes of naked helium stars on the helium main sequence and leads to higher effective temperatures and luminosities. For naked helium stars with masses lower than about 0.8 Mo, they hardly become giant stars as a result of a weak burning shell. However, naked helium stars with masses between about 0.8 M⊙ and 1.1 M⊙ can evolve into giant branch phases, and finally become carbon oxygen white dwarfs.展开更多
Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar...Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar neutrino luminosity with different masses.The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated.We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61×10^9 yr is consistent with that of the Sun.In general,neutrinos are produced by nuclear reactions,and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity.However,neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙.Although the helium flash does not produce neutrinos,plasma decay,one of the thermal processes,can efficiently make neutrinos during this stage.Due to the high mass-loss rate,a star with a mass of 9 M⊙ does not undergo the helium flash.Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage.At the end of the AGB stage,its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.展开更多
Photometric observations in Sloan 9＇ and i＇ bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7＋385531 and VSX J062624.4＋570907, are presented. The light curve solutions reveal that all targets hav...Photometric observations in Sloan 9＇ and i＇ bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7＋385531 and VSX J062624.4＋570907, are presented. The light curve solutions reveal that all targets have overcontact configurations with fillout factors within 0.15-0.26. Their components are G-K spectral types and are almost in thermal contact. They are also relatively close in size and luminosity： the radius ratios r2/r1 are within 0.75-0.90; the luminosity ratios 12/11 are within 0.53-0.63. The results of the light curve solution of CSS J004004.7＋385531 imply the weak limb-darkening effect of its primary component and possible presence of additional absorbing features in the system.展开更多
We report the detection of a large sample of high-α-metal-rich stars on the low giant branch with 2.6<log g<3.3 dex in the LAMOST-MRS survey.This special group corresponds to an intermediate-age population of 5...We report the detection of a large sample of high-α-metal-rich stars on the low giant branch with 2.6<log g<3.3 dex in the LAMOST-MRS survey.This special group corresponds to an intermediate-age population of 5-9 Gyr based on the[Fe/H]-[C/N]diagram and age-[C/N]calibration.A comparison group is selected to have a solarαratio at super metallicity,which is young and has a narrow age range around 3 Gyr.Both groups have thin-disk like kinematics but the former shows slightly large velocity dispersions.The special group shows a larger extension in a vertical distance toward 1.2 kpc,a second peak at smaller Galactic radius and a larger fraction of super metal rich stars with[Fe/H]>0.2 than the comparison group.These properties strongly indicate its connection with the outer bar/bulge region at R=3-5 kpc.A tentative interpretation of this special group is that its stars were formed in the X-shaped bar/bulge region,close to its corotation radius,where radial migration is the most intense,and brings them to present locations at 9 kpc and beyond.Low eccentricities and slightly outward radial excursions of its stars are consistent with this scenario.Its kinematics(cold)and chemistry([α/Fe]~0.1)further support the formation of the instability-driven X-shaped bar/bulge from the thin disk.展开更多
In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The st...In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The stars span a range of 0.55-1.2 mag in color g-i,-0.3--2.5 in metallicity[Fe/H],and have values of surface gravity log g smaller than 3.5 dex.As in the case of main-sequence(MS)stars,the intrinsic widths of loci of red giants are also found to be quite narrow,a few mmag at maximum.There are however systematic differences between the metallicity-dependent stellar loci of red giants and MS stars.The colors of red giants are less sensitive to metallicity than those of MS stars.With good photometry,photometric metallicities of red giants can be reliably determined by fitting the u-g,g-r,r-i,and i-z colors simultaneously to an accuracy of 0.2-0.25 dex,comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10.By comparing fitting results to the stellar loci of red giants and MS stars,we propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry.The technique achieves completeness of~70 per cent and efficiency of~80 per cent in selecting metal-poor red giant stars of[Fe/H]≤-1.2.It thus provides an important tool to probe the structure and assemblage history of the Galactic halo using red giant stars.展开更多
We report the discovery of two r-process-enhanced stars with [Fe/H]>-0.6 dex selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) survey.Three candidate stars have been selected from ...We report the discovery of two r-process-enhanced stars with [Fe/H]>-0.6 dex selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) survey.Three candidate stars have been selected from the LAMOST medium-resolution(R~ 7500) spectroscopic survey,and the follo wed-up high signal-to-noise ratio and high-resolution(R~31,500) spectra are obtained with the ARC Echelle Spectrograph mounted on the3.5 m telescope at the Apache Point Observatory,which allow us for the determination of stellar atmospheric parameters and abundances of 20 elements.Among these three r-process-enhanced candidate stars,TYC 1710-933-1 and TYC 2858-372-1 have [Eu/Fe] higher than 0.3 dex and [Ba/Eu] lower than 0.0 dex,thus,can be identified as new r-process-enhanced objects.TYC 2858-372-1 shows similar r+s-process pattern to the Sun.TYC 1710-933-1 presents enhancement of the r-process elements of Nd and Eu.Our work indicates that the enrichment mechanisms of the heavy neutron-capture elements are complicated for metal-rich stars.展开更多
Photometric observations are presented in V and I bands of six eclipsing binaries at the lower limit of the orbital periods for W UMa stars. Three of them are newly discovered eclipsing systems. The light curve soluti...Photometric observations are presented in V and I bands of six eclipsing binaries at the lower limit of the orbital periods for W UMa stars. Three of them are newly discovered eclipsing systems. The light curve solutions reveal that all shortperiod targets are contact or overcontact binaries and six new binaries are added to the family of short-period systems with estimated parameters. Four binaries have com- ponents that are equal in size and a mass ratio near 1. The phase variability shown by the V-I colors of all targets may be explained by lower temperatures on their back surfaces than those on their side surfaces. Five systems exhibit the O＇Connell effect that can be modeled by cool spots on the side surfaces of their primary components. The light curves of V1067 Her in 2011 and 2012 are fitted by diametrically opposite spots. Applying the criteria for subdivision of W UMa stars to our targets leads to ambiguous results.展开更多
We present model atmosphere analysis for a sample of B-type stars in optical region to obtain their fundamental parameters e.g. effective temperature, surface gravities, and rotational velocities. Approximate masses f...We present model atmosphere analysis for a sample of B-type stars in optical region to obtain their fundamental parameters e.g. effective temperature, surface gravities, and rotational velocities. Approximate masses for the sample of stars under study are obtained by comparing the resulted effective temperatures and surface gravities with the evolutionary tracks. Comparison between these masses and the empirical effective temperatures-mass relation revealed good agreement.展开更多
The luminosity function (LF) for stars is here fitted by a Schechter function and by a Gamma probability density function. The dependence of the number of stars on the distance, both in the low and high luminosity reg...The luminosity function (LF) for stars is here fitted by a Schechter function and by a Gamma probability density function. The dependence of the number of stars on the distance, both in the low and high luminosity regions, requires the inclusion of a lower and upper boundary in the Schechter and Gamma LFs. Three astrophysical applications for stars are provided: deduction of the parameters at low distances, behavior of the average absolute magnitude with distance, and the location of the photometric maximum as a function of the selected flux. The use of the truncated LFs allows modeling the Malmquist bias.展开更多
基金Supported by the National Natural Science Foundation of China
文摘The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function of the properties of the host star, we must accurately determine the parameters of the EH stars first. For this rea- son, we constructed a grid of stellar models including diffusion and rotation-induced extra-mixing with given ranges of input parameters （i.e. mass, metallicity and initial rotation rate）. In addition to the commonly used observational constraints such as the effective temperature Tell, luminosity L and metallicity [Fe/H], we added two obser- vational constraints, the lithium abundance log N （Li） and the rotational period Prot. These two additional observed parameters can set further constraints on the model due to their correlations with mass, age and other stellar properties. Hence, our estimations of the fundamental parameters for these EH stars and their planets have a higher preci- sion than previous works. Therefore, the combination of rotational period and lithium helps us to obtain more accurate parameters for stars, leading to an improvement in knowledge about the physical state of EH stars and their planets.
基金supported by grants from the National Natural Science Foundation of China (Nos. 10503011,10533050 and 10803023)the Natural Science Foundation Project of CQ CSTC (2008BB0153)and the Chinese Academy of Sciences
文摘We collected almost all Highly Processed Data Products （HPDP） of ISO SWS01 spectra for the Galactic visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich proto-planetary nebulae （PPNs）.Those infrared spectra are primarily analyzed and discussed.It is shown that either spectral shapes/peaks,or main molecular/dust features are evidenced to change in the sequence of visual carbon stars,infrared carbon stars,extreme carbon stars and carbon-rich PPNs.Statistically,in this sequence,continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths.In addition,in this sequence,intensities of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths.Furthermore,from 2MASS and IRAS photometric data,the sequence is also proved.Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy,that is the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars → carbon-rich PPNs.
基金supported by National Key R&D Program of China No.2019YFA0405102,2019YFA0405500National Natural Science Foundation of China(NSFC,Grant Nos.11903027,11973001,11833006,U1731108,12090040and 12090044)+2 种基金Funding for the Sloan Digital Sky SurveyⅣhas been provided by the Alfred P.Sloan Foundationthe U.S.Department of Energy Office of Sciencesupport and resources from the Center for High-Performance Computing at the University of Utah。
文摘We present an updated catalog of 46,753 radial velocity(RV)standard stars selected from the APOGEE DR17.These stars cover the Northern and Southern Hemispheres almost evenly,with 62%being red giants and 38%being main sequence stars.These RV standard stars are stable on a baseline longer than 200 days(with 54%longer than one year and 10%longer than five years)with a median stability better than 215 m s~(-1).The average number of observations of those stars is 5 and each observation is required to have signal-to-noise ratio greater than50 and RV measurement error smaller than 500 m s~(-1).Based on the new APOGEE RV standard star catalog,we have checked the RV zero-points(RVZPs)for current large-scale stellar spectroscopic surveys including RAVE,LAMOST,GALAH and Gaia.By careful analysis,we estimate their mean RVZP to be+0.149 kms~(-1),+4.574 km s~(-1)(for LRS),-0.031 km s~(-1)and+0.014 kms~(-1),respectively,for the four surveys.In the RAVE,LAMOST(for MRS),GALAH and Gaia surveys,RVZP exhibits a systematic trend with stellar parameters(mainly[Fe/H],T_(eff),log g,G_(BP)-G_(RP)and G_(RVS)).The corrections to those small but clear RVZPs are of vital importance for these massive spectroscopic surveys in various studies that require extremely high RV accuracies.
基金Supported by the National Natural Science Foundation of China.
文摘The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum （LRS） database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10μm and/or 18 μm. These newly identified stars are located in the Regions Ilia and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.
基金supported partly by project DN08/20 of Scientific Foundation of the Bulgarian Ministry of Education and Scienceproject RD 0-92/2019 of Shumen Universitythe support of the private IRIDA OBSERVATORY。
文摘We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.
基金supported in part by the Pre-phase Studies of Space Science Projects of the Chinese Academy of Sciences,National Basic Research Program of China(973 Project, 2009CB824800)the National Natural Science Foundation of China (Grant No.11073042)funded by the National Aeronautics and Space Administration
文摘In the Wide-field Infrared Survey Explorer （WISE） all-sky source catalog there are 76 million mid-infrared point sources that were detected in the first three WISE bands and have association with only one 2MASS near-IR source within 3. We search for their identifications in the SIMBAD database and find 3.2 million identified sources. Based on these known sources, we establish three criteria for selecting candidate asymptotic giant branch （AGB） stars in the Galaxy, which are three defined zones in a color-color diagram, Galactic latitude ｜b｜ 〈 20°, and ＂corrected＂ WISE third-band W3c≤ 11. Applying these criteria to the WISE＋2MASS sources, 1.37 million of them are selected. We analyze the WISE third-band W3 distribution of the selected sources, and further establish that W3〈8 is required in order to exclude a large fraction of normal stars from them. We therefore find 0.47 million candidate AGB stars in our Galaxy from the WISE source catalog. Using W3c, we estimate their distances and derive their Galactic distributions. The candidates are generally distributed around the Galactic center uniformly, with 68% （1-σ） of them within approximately 8 kpc. We discuss the idea that optical spectroscopy can be used to verify the C-rich AGB stars in our candidates, and thus a fraction of them （-10%） will be good targets for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） survey that is planned to start in fall of 2012.
文摘We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612 MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygen- rich stars must be done with caution, because, in general, it has only a statistical meaning.
基金supported by the Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences (Grant No. XDB09000000)the National Key Basic Research Program of China (2014CB845700)CL acknowledges the National Natural Science Foundation of China (NSFC, Grant Nos. 11373032, 11333003 and U1231119)
文摘In this work, we select spectra of stars with high signal-to-noise ratio from LAMOST data and map their MK classes to the spectral features. The equivalent widths of prominent spectral lines, which play a similar role as multi-color photometry, form a clean stellar locus well ordered by MK classes. The advantage of the stellar locus in line indices is that it gives a natural and continuous classification of stars consistent with either broadly used MK classes or stellar astrophysical parameters. We also employ an SVM-based classification algorithm to assign MK classes to LAMOST stellar spectra. We find that the completenesses of the classifications are up to 90% for A and G type stars, but they are down to about 50% for OB and K type stars. About 40% of the OB and K type stars are mis-classified as A and G type stars,respectively. This is likely due to the difference in the spectral features between late B type and early A type stars or between late G and early K type stars being very weak. The relatively poor performance of the automatic MK classification with SVM suggests that the direct use of line indices to classify stars is likely a more preferable choice.
基金supported partly by project DN 08/20 of the Scientific Foundation of the Bulgarian Ministry of Education and Scienceproject RD-08-142 of Shumen University
文摘Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type （temperatures T1 = T2 = 6100 K）. NSVS 2569022 undergoes a total eclipse of W subtype and the mass ratio is well-determined. Its extremely small value of only 0.077 implies that the target will probably experience instability and a possible merger. This value ranks NSVS 2569022 in sixth place among binaries with the smallest mass ratio. Based on an empirical relation of ＂period - total mass＂ for low mass-ratio binaries, we estimate the global parameters of NSVS 2569022： masses M1 = 1.17 M⊙ and M2 = 0.09 M⊙; radii R1 = 1.19 R⊙ and R2 = 0.38 R⊙; luminosities L1 = 1.73 L⊙ and L2 = 0.17L⊙. An analysis of the characteristics of binaries with extremely low-mass ratios is made. NSVS 2569022 turns out to be a peculiar binary among W UMa stars with extremely small mass ratios due to its unexpectedly small fill-out factor of only 0.014 （slightly overcontact configuration）.
基金Funding for the project has been provided by the National Development and Reform CommissionFunding for the DPAC has been provided by national institutions,in particular the institutions participating in the Gaia Multilateral Agreement
文摘We present LAMOST data on 168 γ Doradus(γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period(P), temperature(T), gravitational acceleration(log(g)) and metallicity [Fe/H] are shown. It is found that most γ Dor variables are main-sequence stars with early F spectral types and temperatures from 6880 K to7280 K. They are slightly more metal poor than the Sun with a metallicity range from-0.4 to 0. On the H-R and log g-T diagrams, both the γ Dor and δ Scuti(δ Sct) stars occupy in the same region and some are beyond the borders predicted by current stellar pulsation theories. It is discovered that the physical properties of γ Dor stars are similar to those of long-period δ Sct(P > 0.3 d) stars. The stellar atmospheric parameters are all correlated with the pulsation period for short-period δ Sct variables(P < 0.3 d), but there are no such relations for γ Dor or long-period δ Sct stars. These results reveal that γ Dor and long-period δ Sct are the same group of pulsating stars and they are different from short-period δ Sct variables. Meanwhile, 33γ Dor stars are identified as candidates of binary or multiple systems.
基金supported by the National Key Basic Research Program of China(2014CB84570)the European Research Council under the European Community’s Seventh Framework Programme(FP7/20072013)/ERC grant agreement(No 338251,Stellar Ages)+1 种基金The Guo Shou Jing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST)is a National Major Scientific Project built by the Chinese Academy of SciencesFunding for the project has been provided by the National Development and Reform Commission
文摘Asteroseismology allows for deriving precise values of the surface gravity of stars. The accurate asteroseismic determinations now available for the large number of stars in the Kepler fields can be used to check and calibrate surface gravities that are currently being obtained spectroscopically for a huge number of stars targeted by large-scale spectroscopic surveys, such as the on-going Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） Galactic survey. The LAMOST spectral surveys have obtained a large number of stellar spectra in the Kepler fields. Stellar atmospheric parameters of those stars have been determined with the LAMOST Stellar Parameter Pipeline at Peking University （LSP3）, by template matching with the MILES empirical spectral library. In the current work, we compare surface gravities yielded by LSP3 with those of two asteroseismic samples-- the largest Kepler asteroseismic sample and the most accurate Kepler asteroseismic sample. We find that LSP3 surface gravities are in good agreement with asteroseismic values of Hekker et al., with a dispersion of -0.2 dex. Except for a few cases, asteroseismic surface gravities ofHuber et al. and LSP3 spectroscopic values agree for a wide range of surface gravities. However, some patterns in the differences can be identified upon close inspection. Potential ways to further improve the LSP3 spectroscopic estimation of stellar atmospheric parameters in the near future are briefly discussed. The effects of effective temperature and metallicity on asteroseismic determinations of surface gravities for giant stars are also discussed.
基金supported by the Xinjiang Science Fund for Distinguished Young Scholars under Grant Nos. 2013721014 and 2014721015the National Natural Science Foundation of China under Grant Nos. 11473024, 11363005 and 11163005
文摘Using stellar evolutionary models, we investigate the effects of convective overshooting on naked helium stars. We find that a larger value of overshooting parameter δov results in a larger convective core, which prolongs the lifetimes of naked helium stars on the helium main sequence and leads to higher effective temperatures and luminosities. For naked helium stars with masses lower than about 0.8 Mo, they hardly become giant stars as a result of a weak burning shell. However, naked helium stars with masses between about 0.8 M⊙ and 1.1 M⊙ can evolve into giant branch phases, and finally become carbon oxygen white dwarfs.
基金support of the National Natural Science Foundation of China(Grant Nos.11763007,11473024,11463005,11863005,11803026 and 11503008)the Tianshan Youth Project of Xinjiang(2017Q014)
文摘Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar neutrino luminosity with different masses.The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated.We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61×10^9 yr is consistent with that of the Sun.In general,neutrinos are produced by nuclear reactions,and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity.However,neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙.Although the helium flash does not produce neutrinos,plasma decay,one of the thermal processes,can efficiently make neutrinos during this stage.Due to the high mass-loss rate,a star with a mass of 9 M⊙ does not undergo the helium flash.Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage.At the end of the AGB stage,its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.
基金supported partly by funds of project RD 08-244 of Scientific Foundation of Shumen Universitythe AAVSO Photometric All-Sky Survey(APASS),funded by the Robert Martin Ayers Sciences Fund
文摘Photometric observations in Sloan 9＇ and i＇ bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7＋385531 and VSX J062624.4＋570907, are presented. The light curve solutions reveal that all targets have overcontact configurations with fillout factors within 0.15-0.26. Their components are G-K spectral types and are almost in thermal contact. They are also relatively close in size and luminosity： the radius ratios r2/r1 are within 0.75-0.90; the luminosity ratios 12/11 are within 0.53-0.63. The results of the light curve solution of CSS J004004.7＋385531 imply the weak limb-darkening effect of its primary component and possible presence of additional absorbing features in the system.
基金supported by the National Natural Science Foundation of China(Nos.11988101,11625313,11890694,11973048 and 11927804)the 2-m Chinese Space Survey Telescope project and the National Key R&D Program of China(No.2019YFA0405502)+2 种基金supported by the Astronomical Big Data Joint Research Center,co-founded by the National Astronomical Observatories,Chinese Academy of Sciences and the Alibaba CloudThe Guo Shou Jing 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。
文摘We report the detection of a large sample of high-α-metal-rich stars on the low giant branch with 2.6<log g<3.3 dex in the LAMOST-MRS survey.This special group corresponds to an intermediate-age population of 5-9 Gyr based on the[Fe/H]-[C/N]diagram and age-[C/N]calibration.A comparison group is selected to have a solarαratio at super metallicity,which is young and has a narrow age range around 3 Gyr.Both groups have thin-disk like kinematics but the former shows slightly large velocity dispersions.The special group shows a larger extension in a vertical distance toward 1.2 kpc,a second peak at smaller Galactic radius and a larger fraction of super metal rich stars with[Fe/H]>0.2 than the comparison group.These properties strongly indicate its connection with the outer bar/bulge region at R=3-5 kpc.A tentative interpretation of this special group is that its stars were formed in the X-shaped bar/bulge region,close to its corotation radius,where radial migration is the most intense,and brings them to present locations at 9 kpc and beyond.Low eccentricities and slightly outward radial excursions of its stars are consistent with this scenario.Its kinematics(cold)and chemistry([α/Fe]~0.1)further support the formation of the instability-driven X-shaped bar/bulge from the thin disk.
基金the National Natural Science Foundation of China(Nos.12173007,11603002)the National Key Basic R&D Program of China(2019YFA0405503)+5 种基金Beijing Normal University(No.310232102)the science research grants from the China Manned Space Project with No.CMS-CSST-2021-A08 and CMS-CSST2021-A09Funding for SDSS-III has been provided by the Alfred P.Sloan Foundationthe Participating Institutionsthe National Science Foundationthe U.S.Department of Energy Office of Science。
文摘In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The stars span a range of 0.55-1.2 mag in color g-i,-0.3--2.5 in metallicity[Fe/H],and have values of surface gravity log g smaller than 3.5 dex.As in the case of main-sequence(MS)stars,the intrinsic widths of loci of red giants are also found to be quite narrow,a few mmag at maximum.There are however systematic differences between the metallicity-dependent stellar loci of red giants and MS stars.The colors of red giants are less sensitive to metallicity than those of MS stars.With good photometry,photometric metallicities of red giants can be reliably determined by fitting the u-g,g-r,r-i,and i-z colors simultaneously to an accuracy of 0.2-0.25 dex,comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10.By comparing fitting results to the stellar loci of red giants and MS stars,we propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry.The technique achieves completeness of~70 per cent and efficiency of~80 per cent in selecting metal-poor red giant stars of[Fe/H]≤-1.2.It thus provides an important tool to probe the structure and assemblage history of the Galactic halo using red giant stars.
基金supported by the National Key R&D Program of China No. 2019YFA0405502the National Natural Science Foundation of China under grant Nos. 12090040, 12090044, 11833006, 12022304, 11973052, 11973042 and U2031144+4 种基金the science research grants from the China Manned Space Project with NO.CMS-CSST-2021B05the supports from Youth Innovation Promotion Association (id. 2019060), Chinese Academy of SciencesPhysics Frontier Center/JINA Center for the Evolution of the Element (JINA-CEE), awarded by the US National Science Foundationpartially supported by the Open Project Program of the Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of SciencesGuo Shou Jing Telescope (the Large Sky Area MultiObject 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 Commission。
文摘We report the discovery of two r-process-enhanced stars with [Fe/H]>-0.6 dex selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) survey.Three candidate stars have been selected from the LAMOST medium-resolution(R~ 7500) spectroscopic survey,and the follo wed-up high signal-to-noise ratio and high-resolution(R~31,500) spectra are obtained with the ARC Echelle Spectrograph mounted on the3.5 m telescope at the Apache Point Observatory,which allow us for the determination of stellar atmospheric parameters and abundances of 20 elements.Among these three r-process-enhanced candidate stars,TYC 1710-933-1 and TYC 2858-372-1 have [Eu/Fe] higher than 0.3 dex and [Ba/Eu] lower than 0.0 dex,thus,can be identified as new r-process-enhanced objects.TYC 2858-372-1 shows similar r+s-process pattern to the Sun.TYC 1710-933-1 presents enhancement of the r-process elements of Nd and Eu.Our work indicates that the enrichment mechanisms of the heavy neutron-capture elements are complicated for metal-rich stars.
基金partly supported by funds provided by projects RD 02-263 administered by the Scientific Foundation of Shumen Universitya joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology+1 种基金funded by the National Aeronautics and Space Administrationthe National Science Foundation
文摘Photometric observations are presented in V and I bands of six eclipsing binaries at the lower limit of the orbital periods for W UMa stars. Three of them are newly discovered eclipsing systems. The light curve solutions reveal that all shortperiod targets are contact or overcontact binaries and six new binaries are added to the family of short-period systems with estimated parameters. Four binaries have com- ponents that are equal in size and a mass ratio near 1. The phase variability shown by the V-I colors of all targets may be explained by lower temperatures on their back surfaces than those on their side surfaces. Five systems exhibit the O＇Connell effect that can be modeled by cool spots on the side surfaces of their primary components. The light curves of V1067 Her in 2011 and 2012 are fitted by diametrically opposite spots. Applying the criteria for subdivision of W UMa stars to our targets leads to ambiguous results.
文摘We present model atmosphere analysis for a sample of B-type stars in optical region to obtain their fundamental parameters e.g. effective temperature, surface gravities, and rotational velocities. Approximate masses for the sample of stars under study are obtained by comparing the resulted effective temperatures and surface gravities with the evolutionary tracks. Comparison between these masses and the empirical effective temperatures-mass relation revealed good agreement.
文摘The luminosity function (LF) for stars is here fitted by a Schechter function and by a Gamma probability density function. The dependence of the number of stars on the distance, both in the low and high luminosity regions, requires the inclusion of a lower and upper boundary in the Schechter and Gamma LFs. Three astrophysical applications for stars are provided: deduction of the parameters at low distances, behavior of the average absolute magnitude with distance, and the location of the photometric maximum as a function of the selected flux. The use of the truncated LFs allows modeling the Malmquist bias.
