Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of α Cen B to satisfy the latest nonasteroseismic and asteroseismic observationa...Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of α Cen B to satisfy the latest nonasteroseismic and asteroseismic observational constraints. We find that the effects can induce a change of about 0.3 μHz in the large frequency spacings and can speed up the star＇s evolution. The model of a Cen B has thereby been improved.展开更多
We present a long-term time-resolved photometry of the short-period eclipsing binary IU Per. It confirms the intrinsic 6 Scuti-like pulsation of the system reported by Kim et al.. With the obtained data, an orbital pe...We present a long-term time-resolved photometry of the short-period eclipsing binary IU Per. It confirms the intrinsic 6 Scuti-like pulsation of the system reported by Kim et al.. With the obtained data, an orbital period study and an eclipsing light curve synthesis based on the Wilson-Devinney method were carded out. The photometric solution reveals a semi-detached configuration with the less-massive component filling its own Roche-lobe. By subtracting the eclipsing light changes from the data, we obtained the pure pulsating light curve of the mass-accreting primary component. A Fourier analysis reveals four pulsation modes with confidence larger than 99%. A mode identification based on the results of the photometric solution was made. It suggests that the star may be in radial pulsation with a fundamental period of about 0.0628 d. A brief discussion concerning the evolutionary status and the pulsation nature is finally given.展开更多
About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than10 km s^(-1) and they ...About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than10 km s^(-1) and they are possible spectroscopic binary or variable candidates(SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s^(-2). The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g～4.621 and lower T ～ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has logg around 4.171 cm s^(-2) that includes binaries and pulsating stars such as δSet and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage.The last group is composed of giants or supergiants with log g around 2.461 cm s^(-2) that may be evolved pulsating stars. One target(C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.展开更多
Using a non-local and time-dependent theory of convection, we have cal- culated the linear non-adiabatic oscillations of the radial and low-degree F-p39 modes for evolutionary models from the main sequence to the asym...Using a non-local and time-dependent theory of convection, we have cal- culated the linear non-adiabatic oscillations of the radial and low-degree F-p39 modes for evolutionary models from the main sequence to the asymptotic giant branch for stars with solar abundance （X = 0.70, Z = 0.02） in the mass range of 0.6-3.0 3//o. The results show that iow luminosity cool stars tend to be solar-like oscillators, whose low-order modes are stable, but intermediate and high order p-modes are pulsationally unstable; their unstable modes have a wide range in frequency and small values for amplitude growth rates. For stars with increasing luminosity and therefore lower tem- perature, the unstable modes shift towards lower orders, the corresponding range of frequency decreases, and the amplitude growth rate increases. High luminosity red gi- ant stars behave like typical Mira-like oscillators. The effects of the coupling between convection and oscillations on pulsational instability have been carefully analyzed in this work. Our research shows that convection does not simply act as a damping mechanism for oscillations, and the complex nature of the coupling between convec- tion and oscillations makes turbulent convection sometimes behave as damping, and sometimes as excitation. Such a picture can not only naturally account for the red edge of the instability strip, but also the solar-like oscillations in low luminosity red stars and Mira-like ones in high luminosity red giants.展开更多
Non-radial p modes and g modes appear simultaneously in red giant stars. Their frequencies have different variation rates,causing their frequencies to become close during stellar evolution so that avoided crossings ap...Non-radial p modes and g modes appear simultaneously in red giant stars. Their frequencies have different variation rates,causing their frequencies to become close during stellar evolution so that avoided crossings appear.The separation between regions where acoustic waves and gravity waves propagate for l=1,2 and 3 is different,which results in the coupling efficiency also being different.We present the results of numerical computations of the models we study.We find that the two kinds of modes for l=2 and 3 need to be closer in frequency in order for a complete exchange to occur,compared to the case for modes with l=1.Their scaled oscillation frequencies also present better regularity with evolution than modes with l=1. In order to study the effect of the avoided crossings in detail,we set the mode which has the smallest mode inertia to be the p mode.We plot the two kinds of modes for l =1,2 and 3 in frequency and periodéchelle diagrams and find modes of l=2 and 3 fit the two relations better;they are more equally spaced in frequency and period than modes with l=1.Under careful observation of the two kinds oféchelle diagrams for l=2 and 3,we still find that some p modes shift a little from being equally spaced in frequency and some g modes,which are close to those p modes in period,shift a little from being equally spaced in period.Then,we study the relation between the deviation from period being equally spaced and the mode inertia of g modes for different l.The g modes of l=1 with a period closer to the p mode have less inertia and the deviation is bigger in the periodéchelle diagram.Their deviation is also obvious. However g modes of l=2 and 3 shift a little or have almost no deviation from being equally spaced in period,even though some of them may have strong coupling and close mode inertia like in the p modes.So,we suggest a possible method for measuring period spacing of g modes precisely using mixed g modes with l=2 and 3 that have fewer observed mixed g modes than for l=1.展开更多
UV Tri was observed photometrically from 1999 to 2000 at the Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences, and was also observed with Stromgren uvbyHβ filter system at the ...UV Tri was observed photometrically from 1999 to 2000 at the Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences, and was also observed with Stromgren uvbyHβ filter system at the Sierra Nevada Observatory (Spain) in 2000. From period analyses of the data, three pulsation frequencies, 9.3299 c d-1 10.8483 cd-1 and 3.6035 cd-1 were obtained. We derived color indices: b - y = 0.215, m1 = 0.169, c1 = 0.783, and β = 2.775. With these indices and some calibrations, we obtain: Mv = 2.44, Mbol = 2.27, logL/L = 0.99, and log Teff = 3.875. Evolutionary sequences of stellar models with 1.00-2.00 solar masses, at steps of 0.05 M, are computed. Each sequence consists of 220 evolutionary intervals. From a comparison between the observed and calculated physical parameters we conclude that UV Thi is in an early evolutionary phase before the turn-off point.展开更多
We test the possible evolutionary tracks of stars with various masses （1.8 M,1.9 M,2.0 M,2.1 M,2.2 M）and metallicities Z（0.008,0.010, 0.012）,including both models with and without convective core overshooting.At a...We test the possible evolutionary tracks of stars with various masses （1.8 M,1.9 M,2.0 M,2.1 M,2.2 M）and metallicities Z（0.008,0.010, 0.012）,including both models with and without convective core overshooting.At a given mass and metallicity,the models with a larger overshoot predict a larger radius and age of the star.Based on the observed frequency of oscillations and the position of Oph on the H-R diagram,we obtain two distinct better-fitting models：the solutions with mass M=1.9 M favor a radius in the range 10.55±0.03 R with an age of 1.01±0.08 Gyr;the solutions with mass M=2.0 M favor a radius in the range 10.74±0.03 R with an age of 0.95±0.11 Gyr.Furthermore,we investigate the influence of overshooting on the internal structure and the pulsation properties,and find that increasing the convective core overshoot significantly decreases non-radial mode inertia,while also increasing the mode amplitude.Therefore,the estimation of stellar mass and age might be modified by convective core penetration.展开更多
We present time-series CCD photometry of V551 Aur, an eclipsing binary located in the open cluster NGC 2126 that shows δ Scuti-like pulsations. Complete covered light curves in theBand V bands were obtained with high...We present time-series CCD photometry of V551 Aur, an eclipsing binary located in the open cluster NGC 2126 that shows δ Scuti-like pulsations. Complete covered light curves in theBand V bands were obtained with high-precision over nine nights. Based on them, a revised orbital period and the first photometric solutions were determined. Our eclipsing light-curve synthesis reveals a detached configura- tion for the binary system with a mass-ratio of about 0.73, and the mean density of the pulsating primary component was deduced to be about （0.532±0.005）ρ. A fre- quency analysis of the eclipse-subtracted light curve yields two reliable frequencies at f1=7.727013（c/d） and f2=15.45403（c/d）, respectively. With the help of the derived mean density, mode identification was performed. The result suggests that the primary component of V551 Aur is very probably g-mode oscillations.展开更多
基金The Ministry of Science and Technology of the People's Republic of China through Grant 2007CB815406the NSFC through Grants 10173021,10433030,10773003 and 10778601
文摘Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of α Cen B to satisfy the latest nonasteroseismic and asteroseismic observational constraints. We find that the effects can induce a change of about 0.3 μHz in the large frequency spacings and can speed up the star＇s evolution. The model of a Cen B has thereby been improved.
基金Supported by the National Natural Science Foundation of China
文摘We present a long-term time-resolved photometry of the short-period eclipsing binary IU Per. It confirms the intrinsic 6 Scuti-like pulsation of the system reported by Kim et al.. With the obtained data, an orbital period study and an eclipsing light curve synthesis based on the Wilson-Devinney method were carded out. The photometric solution reveals a semi-detached configuration with the less-massive component filling its own Roche-lobe. By subtracting the eclipsing light changes from the data, we obtained the pure pulsating light curve of the mass-accreting primary component. A Fourier analysis reveals four pulsation modes with confidence larger than 99%. A mode identification based on the results of the photometric solution was made. It suggests that the star may be in radial pulsation with a fundamental period of about 0.0628 d. A brief discussion concerning the evolutionary status and the pulsation nature is finally given.
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 Sciencesprovided by the National Development and Reform Commission
文摘About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than10 km s^(-1) and they are possible spectroscopic binary or variable candidates(SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s^(-2). The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g～4.621 and lower T ～ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has logg around 4.171 cm s^(-2) that includes binaries and pulsating stars such as δSet and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage.The last group is composed of giants or supergiants with log g around 2.461 cm s^(-2) that may be evolved pulsating stars. One target(C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.
基金Supported by the National Natural Science Foundation of China
文摘Using a non-local and time-dependent theory of convection, we have cal- culated the linear non-adiabatic oscillations of the radial and low-degree F-p39 modes for evolutionary models from the main sequence to the asymptotic giant branch for stars with solar abundance （X = 0.70, Z = 0.02） in the mass range of 0.6-3.0 3//o. The results show that iow luminosity cool stars tend to be solar-like oscillators, whose low-order modes are stable, but intermediate and high order p-modes are pulsationally unstable; their unstable modes have a wide range in frequency and small values for amplitude growth rates. For stars with increasing luminosity and therefore lower tem- perature, the unstable modes shift towards lower orders, the corresponding range of frequency decreases, and the amplitude growth rate increases. High luminosity red gi- ant stars behave like typical Mira-like oscillators. The effects of the coupling between convection and oscillations on pulsational instability have been carefully analyzed in this work. Our research shows that convection does not simply act as a damping mechanism for oscillations, and the complex nature of the coupling between convec- tion and oscillations makes turbulent convection sometimes behave as damping, and sometimes as excitation. Such a picture can not only naturally account for the red edge of the instability strip, but also the solar-like oscillations in low luminosity red stars and Mira-like ones in high luminosity red giants.
基金supported by the National Natural Science Foundation of China (Grant Nos.10973035 and 10673030)the Knowledge Innovation Key Program of the Chinese Academy of Sciences under Grant No.KJCX2-YW-T24the Yunnan Natural Science Foundation(Y1YJ011001)
文摘Non-radial p modes and g modes appear simultaneously in red giant stars. Their frequencies have different variation rates,causing their frequencies to become close during stellar evolution so that avoided crossings appear.The separation between regions where acoustic waves and gravity waves propagate for l=1,2 and 3 is different,which results in the coupling efficiency also being different.We present the results of numerical computations of the models we study.We find that the two kinds of modes for l=2 and 3 need to be closer in frequency in order for a complete exchange to occur,compared to the case for modes with l=1.Their scaled oscillation frequencies also present better regularity with evolution than modes with l=1. In order to study the effect of the avoided crossings in detail,we set the mode which has the smallest mode inertia to be the p mode.We plot the two kinds of modes for l =1,2 and 3 in frequency and periodéchelle diagrams and find modes of l=2 and 3 fit the two relations better;they are more equally spaced in frequency and period than modes with l=1.Under careful observation of the two kinds oféchelle diagrams for l=2 and 3,we still find that some p modes shift a little from being equally spaced in frequency and some g modes,which are close to those p modes in period,shift a little from being equally spaced in period.Then,we study the relation between the deviation from period being equally spaced and the mode inertia of g modes for different l.The g modes of l=1 with a period closer to the p mode have less inertia and the deviation is bigger in the periodéchelle diagram.Their deviation is also obvious. However g modes of l=2 and 3 shift a little or have almost no deviation from being equally spaced in period,even though some of them may have strong coupling and close mode inertia like in the p modes.So,we suggest a possible method for measuring period spacing of g modes precisely using mixed g modes with l=2 and 3 that have fewer observed mixed g modes than for l=1.
基金the National NaturalScience Foundation of China fOr the research grants. ElOy Rodrfguez acknowIedges partialresearch suPport
文摘UV Tri was observed photometrically from 1999 to 2000 at the Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences, and was also observed with Stromgren uvbyHβ filter system at the Sierra Nevada Observatory (Spain) in 2000. From period analyses of the data, three pulsation frequencies, 9.3299 c d-1 10.8483 cd-1 and 3.6035 cd-1 were obtained. We derived color indices: b - y = 0.215, m1 = 0.169, c1 = 0.783, and β = 2.775. With these indices and some calibrations, we obtain: Mv = 2.44, Mbol = 2.27, logL/L = 0.99, and log Teff = 3.875. Evolutionary sequences of stellar models with 1.00-2.00 solar masses, at steps of 0.05 M, are computed. Each sequence consists of 220 evolutionary intervals. From a comparison between the observed and calculated physical parameters we conclude that UV Thi is in an early evolutionary phase before the turn-off point.
基金Supported by the National Natural Science Foundation of Chinasupported by the Ministry of Science and Technology of the People's Republic of China(Grant No.2007CB815406)the National Natural Science Foundation of China(Grant Nos.10773003,10933002 and 10778601)
文摘We test the possible evolutionary tracks of stars with various masses （1.8 M,1.9 M,2.0 M,2.1 M,2.2 M）and metallicities Z（0.008,0.010, 0.012）,including both models with and without convective core overshooting.At a given mass and metallicity,the models with a larger overshoot predict a larger radius and age of the star.Based on the observed frequency of oscillations and the position of Oph on the H-R diagram,we obtain two distinct better-fitting models：the solutions with mass M=1.9 M favor a radius in the range 10.55±0.03 R with an age of 1.01±0.08 Gyr;the solutions with mass M=2.0 M favor a radius in the range 10.74±0.03 R with an age of 0.95±0.11 Gyr.Furthermore,we investigate the influence of overshooting on the internal structure and the pulsation properties,and find that increasing the convective core overshoot significantly decreases non-radial mode inertia,while also increasing the mode amplitude.Therefore,the estimation of stellar mass and age might be modified by convective core penetration.
基金supported by the National Natural Science Foundation of China (GrantNos. 10773015 and 10778719)
文摘We present time-series CCD photometry of V551 Aur, an eclipsing binary located in the open cluster NGC 2126 that shows δ Scuti-like pulsations. Complete covered light curves in theBand V bands were obtained with high-precision over nine nights. Based on them, a revised orbital period and the first photometric solutions were determined. Our eclipsing light-curve synthesis reveals a detached configura- tion for the binary system with a mass-ratio of about 0.73, and the mean density of the pulsating primary component was deduced to be about （0.532±0.005）ρ. A fre- quency analysis of the eclipse-subtracted light curve yields two reliable frequencies at f1=7.727013（c/d） and f2=15.45403（c/d）, respectively. With the help of the derived mean density, mode identification was performed. The result suggests that the primary component of V551 Aur is very probably g-mode oscillations.
