日冕物质抛射(coronal mass ejection,CME)是从太阳上抛出的大团等离子体云.在其他恒星上,类似的现象被称为星冕物质抛射(简称恒星CME).基于对日冕物质抛射的理解,人们相信,星冕物质抛射可能是恒星-系外行星系统中空间天气最主要的驱动...日冕物质抛射(coronal mass ejection,CME)是从太阳上抛出的大团等离子体云.在其他恒星上,类似的现象被称为星冕物质抛射(简称恒星CME).基于对日冕物质抛射的理解,人们相信,星冕物质抛射可能是恒星-系外行星系统中空间天气最主要的驱动源,因而是恒星影响其行星的一个关键途径,在太阳系外的宜居世界形成过程中占有重要地位.此外,在恒星演化的部分时期,频繁发生的CME还可能对恒星的质量和角动量损失有重要贡献.尽管从不同波段的观测数据中,人们认证出了少数的恒星CME候选体,但迄今尚无学界公认的、确切的恒星CME观测证据.本文总结了在不同波段探测恒星CME的可能方法,介绍了目前已经开展的关于恒星CME探测的有益尝试,以及恒星CME及其与系外行星相互作用的建模进展.在对现有研究不足之处进行分析的基础上,本文还探讨了未来恒星CME探测和建模研究的方向.展开更多
We identify 108 M subdwarfs（sd Ms） out of more than two hundred thousand M type spectra from the second data release（DR2） of the LAMOST regular survey. This sample, among which 58 members are identified for the fi...We identify 108 M subdwarfs（sd Ms） out of more than two hundred thousand M type spectra from the second data release（DR2） of the LAMOST regular survey. This sample, among which 58 members are identified for the first time, includes 33 extreme subdwarfs（esd Ms） and 11 ultra subdwarfs（usd Ms）.The selection is based on the usual ratio of absorption depth of Ca H2, Ca H3 and TiO 5 band systems.We also emphasize the use of the Ca H1 band. We provide estimates of spectral subtype（SPT）, L′epine metallicity index ζ, effective temperature and [Fe/H]. Both ζ–[Fe/H] and SPT–Teff figures show reasonable consistency; compared to PHOENIX model spectra, average rounded values of [Fe/H] for sd Ms, esd Ms and usd Ms are respectively –0.5, –1 and –1.5. The photometric distances are estimated, indicating that most sources are located within 500 pc of the Sun and 350 pc of the Galactic disk. Velocities and 3D Galactic motions are also briefly discussed. Among the 108 subdwarfs, seven stars appear to be active with a significant Hα emission line. The source LAMOST J104521.52＋482823.3 is a white dwarf- M subdwarf binary, while LAMOST J123045.52＋410943.8, also active, exhibits carbon features in red.展开更多
We present a method of 13 late-type main-sequence stars chromospheric flux observation data calculations. These Sun-like stars have well-determined cyclic flux variations similar to the 11-year solar activity cycle. O...We present a method of 13 late-type main-sequence stars chromospheric flux observation data calculations. These Sun-like stars have well-determined cyclic flux variations similar to the 11-year solar activity cycle. Our flux prediction is based on chromospheric HK emission time series measurements from the Mount Wilson Observatory and comparable solar data. We show that solar three - component modeling explains well the stellar observations. We find that the 10 - 20% of K - stars disc’s surfaces are occupied by bright active regions.展开更多
The relationship between abundances and orbital parameters for 235 F- and G-type intermediate- and low- mass stars in the Galaxy is analyzed. We foundthat there are abundance gradients in the thin disk in both radial ...The relationship between abundances and orbital parameters for 235 F- and G-type intermediate- and low- mass stars in the Galaxy is analyzed. We foundthat there are abundance gradients in the thin disk in both radial and verticaldirections (-0.116 dex kpc-1 and -0.309 dex kpc-1 respectively). The gradients appear to be flatter as the Galaxy evolves. No gradient is found in the thick disk based on 18 thick disk stars. These results indicate that the ELS model is mainly suitable for the evolution of the thin disk, while the SZ model is more suitable for the evolution of the thick disk. Additionally, these results indicate that in-fall and out-flow processes play important roles in the chemical evolution of the Galaxy.展开更多
In this study,we determined the physical parameters of W UMa type contact binaries and their stability of mass transfer with different stellar mass ranges over a broad space by applying the basic dynamical evolution e...In this study,we determined the physical parameters of W UMa type contact binaries and their stability of mass transfer with different stellar mass ranges over a broad space by applying the basic dynamical evolution equations of the W UMa type contact binaries using accretor and donor masses between 0.079 and 2.79 M_(⊙).In these systems,we have studied the three subclasses of W UMa systems of A-,B-and W-type contact binaries using the initial and final mass ranges and we investigated different stellar and orbital parameters for the subclasses of W UMa systems.We examined the stability of the W UMa type contact binaries using the orbital parameters such as critical mass ratio,Roche lobe radius of the donor star and mass ratio of these systems.Thus,we computed the observed and calculated physical parameters of A-,B-and W-type W UMa systems.Moreover,we determined the combined and color temperatures to classify the three subclasses of the systems.Also,we presented the result of the internal stellar structure and evolution of W UMa type contact binaries by using the polytropic model.展开更多
We present a spectroscopic catalog of 93 619 M dwarfs from the first data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST）general survey. During sample selection, M giant contaminatio...We present a spectroscopic catalog of 93 619 M dwarfs from the first data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST）general survey. During sample selection, M giant contamination was eliminated using2 MASS photometry and Ca H/TiO molecular indices. For each spectrum, the spectral subtype and values are provided including radial velocity, Hα equivalent width, a series of prominent molecular band indices, and the metal–sensitive parameter ζ, as well as distances and the space motions for high S/N objects. In addition, Hα emission lines are measured to examine the magnetic activity properties of M dwarfs and 7179 active ones are found. In particular, a subsample with significant variation in magnetic activity is revealed through observations from different epochs. Finally, statistical analysis for this sample is performed, including the metallicity classification, the distribution of molecular band indices and their errors.展开更多
We present high-precision, multi-band CCD photometry of two less-studied close binaries V1123 Tau and V1128 Tau. Complete covered light curves and a number of new times of light minima of the two eclipsing systems wer...We present high-precision, multi-band CCD photometry of two less-studied close binaries V1123 Tau and V1128 Tau. Complete covered light curves and a number of new times of light minima of the two eclipsing systems were obtained, based on which, revised orbital elements and new ephemerides were given. By adopting the Wilson-Devinney method, the light curves were analyzed. The photometric solutions confirm the W UMa-type nature of the binary systems. With the less-massive secondary slightly cooler than the primary, V1123 Tau could be classified as an A- type contact system. While V1128 Tau is typically considered a W-type W UMa star, the surface temperature of its secondary component is determined to be absolutely higher than the primary by about 270 K. Combining with the results of radial-velocity solutions, we determined absolute parameters of the two systems. The mass, radius and luminosity for each component of V1123 Tau were derived as： 1.36 ±0.05M⊙, 1.37 ± 0.02R⊙, and 2.01± O.07L⊙ and 0.40±0.02M⊙, 0.80±0.01R⊙, and 0.67±0.04L⊙, respectively. For V1128 Tau, the absolute parameters were computed to be 1.09±0.03M⊙, 1.01±0.01R⊙, and 1.34±0.06Le and 0.58 ± 0.01M⊙, 0.76±0.01R⊙, and 0.91±0.05L⊙, respectively. Based on these results, the evolutionary status and the physical nature of the two binary systems are discussed, while also connecting with the theoretical models.展开更多
We monitored the light curves of 22 weak-line T Tauri stars （WTTSs） discovered among the X-ray sources in the field of the Taurus-Auriga cloud. For 12 of the 22 WTTSs photometric periodic variability is confirmed an...We monitored the light curves of 22 weak-line T Tauri stars （WTTSs） discovered among the X-ray sources in the field of the Taurus-Auriga cloud. For 12 of the 22 WTTSs photometric periodic variability is confirmed and their rational periods are determined using Phase Dispersion Minimization （PDM） and Fourier analysis. Most of them are found to have periods shorter than one day. This gives further evidence for the spin up of solar-type stars predicted by the models of angular momentum evolution of pre-main sequence stars.展开更多
We present high-resolution optical echell spectroscopy of HIP 544 and HIP 46843, two nearby solar like stars. The discovery of these young stars at such a close distance to the Sun is really a surprising phenomenon. I...We present high-resolution optical echell spectroscopy of HIP 544 and HIP 46843, two nearby solar like stars. The discovery of these young stars at such a close distance to the Sun is really a surprising phenomenon. It will help us to have a better understanding of the structure and evolutionary history of the Milky Way. The radial velocities （RV） of HIP 544 and HIP 46843 are measured to be -6.88±0.13km s^-1 and 8.30±0.16km s^-1, respectively, which are more accurate than before. The equivalent widths （EW） of the Li I 6707.8A absorption line of HIP 544 and HIP 46843 are measured to be 110±5 mA and 195±5 mA respectively. Based on these properties, HIP 544 is estimated to be 100-800Myr old and HIP 46843 30-100Myr old using three relatively creditable methods.展开更多
Magnetic cataclysmic variables （CVs） contain a white dwarf （WD） with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV （CXOGSG J2155...Magnetic cataclysmic variables （CVs） contain a white dwarf （WD） with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV （CXOGSG J215544.4＋380116） from the Chandra archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source is a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2-M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass （~ 0.4 34⊙） and radius （~0.4 R⊙） for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/radius. The estimated low X-ray luminosity and accretion rate may suggest the source is a low-accretion-rate polar. In addition, Very Large Array observations reveal a possible radio counterpart to the X-ray source, but with a low significance. Further radio observations with high quality are needed to confirm the radio counterpart and explore the properties of this binary system.展开更多
This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources ...This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources all without previously known SiO detections. A tentative SiO emission was detected from the source IRAS18585+0900. The oxygen/carbonrichness of the circumstellar of IRAS18585+0900 is discussed with reference to its IRAS low resolution spectral (LRS) class 41. The low detection rate is discussed.展开更多
We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined r...We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined red clump feature than the APOGEE dataset in the Teff versus log g diagram. With this advantage, we have separated red clump stars from red giant stars, and attempt to establish calibrations between the two datasets for the two groups of stars. The results show that there is a good consistency in temperature with a calibration close to the one-to-one line, and we can establish a satisfactory metallicity calibration of[Fe/H]APOGEE= 1.18[Fe/H]LAMOST ＋ 0.11 with a scatter of ～ 0.08 dex for both the red clump and red giant branch samples. For gravity, there is no correlation for red clump stars between the two datasets, and scatters around the calibrations of red giant stars are substantial. We found two main sources of scatter in log g for red giant stars. One is a group of stars with 0.00253 × Teff- 8.67 〈 log g 〈 2.6 located in the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with position in the Teff versus log g diagram. After excluding stars in these two regions,we have established two calibrations for red giant stars, log g APOGEE = 0.000615 ×Teff,LAMOST＋ 0.697 × log g LAMOST- 2.208（σ = 0.150） for [Fe/H] 〉-1 and log gAPOGEE= 0.000874×Teff,LAMOST＋0.588×log g LAMOST-3.117（σ = 0.167）for [Fe/H] 〈-1. The calibrations are valid for stars with Teff = 3800- 5400 K and log g = 0- 3.8 dex, and are useful in work aiming to combine the LAMOST and APOGEE datasets in a future study. In addition, we find that an SVM method based on asteroseismic log g is a good way to greatly improve the accuracy of gravity for these two regions, at least in the LAMOST dataset.展开更多
This paper presents new CCD BV RI light curves of the newly discovered RS CVn eclipsing binary V1034 Her in 2009 and 2010, the shapes of which are different from previously published results. They show an asymmetric o...This paper presents new CCD BV RI light curves of the newly discovered RS CVn eclipsing binary V1034 Her in 2009 and 2010, the shapes of which are different from previously published results. They show an asymmetric outside eclipse, and we try to use a spot model to explain the phenomenon. Using the Wilson-Devinney program with a one-spot or two-spot model, photometric solutions of the system and starspot parameters were derived. Comparing the two results shows that the case of two spots is more successful in reproducing light-curve distortions. Looking at all the spot longitudes, the trend is towards active longitude belts and each active longitude belt may switch. Comparing the light curves from 2009 and 2010, we can see that the light curve changes over the long time scale of a year, especially in phase 0.25. In addition, we also collected the values of the maximum amplitudes of photometric distortion of the short-period RS CVn binary. We found for the first time that there is a trend of increasing activity with decreasing orbital period. Finally, fitting all available light minimum times including our newly obtained ones with a polynomial function confirmed that the orbital period of V1034 Her increased.展开更多
The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by mea...The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique, and find that the active regions shift oppositely along longitude on a time scale of one day. Combining with the observational data obtained by other groups, we discuss the evolution of spotted regions in the photosphere, and find that its starspots evolve not only on a short time scale but also on a long time scale. The pure chromospheric emissions for Ca IIHK and Hβ lines are derived by using the spectral subtraction technique. The variation of Ca IIHK lines＇ excess emission is spatially correlated to the starspot regions. There is no clear rotational modulation for the Hβ line＇s excess emission, probably due to the contamination of prominence emission.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
By means of a population synthesis code, we investigate the Mira variables. Their birth rate （over 0.65yr^-1） and their number （～ 130000） in the Galaxy are estimated. For all possible Mira variables, ranges of th...By means of a population synthesis code, we investigate the Mira variables. Their birth rate （over 0.65yr^-1） and their number （～ 130000） in the Galaxy are estimated. For all possible Mira variables, ranges of their initial masses,pulsating periods, mass losses and lifetimes are given. We check our model with the observed Mira variables near the Sun and our results prove to be valid.展开更多
文摘日冕物质抛射(coronal mass ejection,CME)是从太阳上抛出的大团等离子体云.在其他恒星上,类似的现象被称为星冕物质抛射(简称恒星CME).基于对日冕物质抛射的理解,人们相信,星冕物质抛射可能是恒星-系外行星系统中空间天气最主要的驱动源,因而是恒星影响其行星的一个关键途径,在太阳系外的宜居世界形成过程中占有重要地位.此外,在恒星演化的部分时期,频繁发生的CME还可能对恒星的质量和角动量损失有重要贡献.尽管从不同波段的观测数据中,人们认证出了少数的恒星CME候选体,但迄今尚无学界公认的、确切的恒星CME观测证据.本文总结了在不同波段探测恒星CME的可能方法,介绍了目前已经开展的关于恒星CME探测的有益尝试,以及恒星CME及其与系外行星相互作用的建模进展.在对现有研究不足之处进行分析的基础上,本文还探讨了未来恒星CME探测和建模研究的方向.
基金partly supported by the National Key Basic Research Program of China(Grant No.2014CB845700)the National Natural Science Foundation of China(Grant No.11390371)+1 种基金a National Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission.LAMOST is operated and managed by National Astronomical Observatories,Chinese Academy of Sciences
文摘We identify 108 M subdwarfs（sd Ms） out of more than two hundred thousand M type spectra from the second data release（DR2） of the LAMOST regular survey. This sample, among which 58 members are identified for the first time, includes 33 extreme subdwarfs（esd Ms） and 11 ultra subdwarfs（usd Ms）.The selection is based on the usual ratio of absorption depth of Ca H2, Ca H3 and TiO 5 band systems.We also emphasize the use of the Ca H1 band. We provide estimates of spectral subtype（SPT）, L′epine metallicity index ζ, effective temperature and [Fe/H]. Both ζ–[Fe/H] and SPT–Teff figures show reasonable consistency; compared to PHOENIX model spectra, average rounded values of [Fe/H] for sd Ms, esd Ms and usd Ms are respectively –0.5, –1 and –1.5. The photometric distances are estimated, indicating that most sources are located within 500 pc of the Sun and 350 pc of the Galactic disk. Velocities and 3D Galactic motions are also briefly discussed. Among the 108 subdwarfs, seven stars appear to be active with a significant Hα emission line. The source LAMOST J104521.52＋482823.3 is a white dwarf- M subdwarf binary, while LAMOST J123045.52＋410943.8, also active, exhibits carbon features in red.
文摘We present a method of 13 late-type main-sequence stars chromospheric flux observation data calculations. These Sun-like stars have well-determined cyclic flux variations similar to the 11-year solar activity cycle. Our flux prediction is based on chromospheric HK emission time series measurements from the Mount Wilson Observatory and comparable solar data. We show that solar three - component modeling explains well the stellar observations. We find that the 10 - 20% of K - stars disc’s surfaces are occupied by bright active regions.
基金the National Natural Science Foundation of China (Grant Nos.10173014 and NKBRSF G1999075406)
文摘The relationship between abundances and orbital parameters for 235 F- and G-type intermediate- and low- mass stars in the Galaxy is analyzed. We foundthat there are abundance gradients in the thin disk in both radial and verticaldirections (-0.116 dex kpc-1 and -0.309 dex kpc-1 respectively). The gradients appear to be flatter as the Galaxy evolves. No gradient is found in the thick disk based on 18 thick disk stars. These results indicate that the ELS model is mainly suitable for the evolution of the thin disk, while the SZ model is more suitable for the evolution of the thick disk. Additionally, these results indicate that in-fall and out-flow processes play important roles in the chemical evolution of the Galaxy.
基金the Space Science and Geospatial Institute (SSGI) -Entoto Observatory and Research Center (EORC)Astronomy and Astrophysics Department for supporting this research。
文摘In this study,we determined the physical parameters of W UMa type contact binaries and their stability of mass transfer with different stellar mass ranges over a broad space by applying the basic dynamical evolution equations of the W UMa type contact binaries using accretor and donor masses between 0.079 and 2.79 M_(⊙).In these systems,we have studied the three subclasses of W UMa systems of A-,B-and W-type contact binaries using the initial and final mass ranges and we investigated different stellar and orbital parameters for the subclasses of W UMa systems.We examined the stability of the W UMa type contact binaries using the orbital parameters such as critical mass ratio,Roche lobe radius of the donor star and mass ratio of these systems.Thus,we computed the observed and calculated physical parameters of A-,B-and W-type W UMa systems.Moreover,we determined the combined and color temperatures to classify the three subclasses of the systems.Also,we presented the result of the internal stellar structure and evolution of W UMa type contact binaries by using the polytropic model.
基金supported by the National Natural Science Foundation of China
文摘We present a spectroscopic catalog of 93 619 M dwarfs from the first data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST）general survey. During sample selection, M giant contamination was eliminated using2 MASS photometry and Ca H/TiO molecular indices. For each spectrum, the spectral subtype and values are provided including radial velocity, Hα equivalent width, a series of prominent molecular band indices, and the metal–sensitive parameter ζ, as well as distances and the space motions for high S/N objects. In addition, Hα emission lines are measured to examine the magnetic activity properties of M dwarfs and 7179 active ones are found. In particular, a subsample with significant variation in magnetic activity is revealed through observations from different epochs. Finally, statistical analysis for this sample is performed, including the metallicity classification, the distribution of molecular band indices and their errors.
基金supported by the National Natural Science Foundation of China(Grant No. 10773015)
文摘We present high-precision, multi-band CCD photometry of two less-studied close binaries V1123 Tau and V1128 Tau. Complete covered light curves and a number of new times of light minima of the two eclipsing systems were obtained, based on which, revised orbital elements and new ephemerides were given. By adopting the Wilson-Devinney method, the light curves were analyzed. The photometric solutions confirm the W UMa-type nature of the binary systems. With the less-massive secondary slightly cooler than the primary, V1123 Tau could be classified as an A- type contact system. While V1128 Tau is typically considered a W-type W UMa star, the surface temperature of its secondary component is determined to be absolutely higher than the primary by about 270 K. Combining with the results of radial-velocity solutions, we determined absolute parameters of the two systems. The mass, radius and luminosity for each component of V1123 Tau were derived as： 1.36 ±0.05M⊙, 1.37 ± 0.02R⊙, and 2.01± O.07L⊙ and 0.40±0.02M⊙, 0.80±0.01R⊙, and 0.67±0.04L⊙, respectively. For V1128 Tau, the absolute parameters were computed to be 1.09±0.03M⊙, 1.01±0.01R⊙, and 1.34±0.06Le and 0.58 ± 0.01M⊙, 0.76±0.01R⊙, and 0.91±0.05L⊙, respectively. Based on these results, the evolutionary status and the physical nature of the two binary systems are discussed, while also connecting with the theoretical models.
基金Supported by the National Natural Science Foundation of China.
文摘We monitored the light curves of 22 weak-line T Tauri stars （WTTSs） discovered among the X-ray sources in the field of the Taurus-Auriga cloud. For 12 of the 22 WTTSs photometric periodic variability is confirmed and their rational periods are determined using Phase Dispersion Minimization （PDM） and Fourier analysis. Most of them are found to have periods shorter than one day. This gives further evidence for the spin up of solar-type stars predicted by the models of angular momentum evolution of pre-main sequence stars.
基金Supported by the National Natural Science Foundation of China.
文摘We present high-resolution optical echell spectroscopy of HIP 544 and HIP 46843, two nearby solar like stars. The discovery of these young stars at such a close distance to the Sun is really a surprising phenomenon. It will help us to have a better understanding of the structure and evolutionary history of the Milky Way. The radial velocities （RV） of HIP 544 and HIP 46843 are measured to be -6.88±0.13km s^-1 and 8.30±0.16km s^-1, respectively, which are more accurate than before. The equivalent widths （EW） of the Li I 6707.8A absorption line of HIP 544 and HIP 46843 are measured to be 110±5 mA and 195±5 mA respectively. Based on these properties, HIP 544 is estimated to be 100-800Myr old and HIP 46843 30-100Myr old using three relatively creditable methods.
基金the National Natural Science Foundation of China(Grant Nos.11273028 and 11333004)support from National Astronomical Observatories,Chinese Academy of Sciences under the Young Researcher Grant
文摘Magnetic cataclysmic variables （CVs） contain a white dwarf （WD） with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV （CXOGSG J215544.4＋380116） from the Chandra archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source is a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2-M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass （~ 0.4 34⊙） and radius （~0.4 R⊙） for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/radius. The estimated low X-ray luminosity and accretion rate may suggest the source is a low-accretion-rate polar. In addition, Very Large Array observations reveal a possible radio counterpart to the X-ray source, but with a low significance. Further radio observations with high quality are needed to confirm the radio counterpart and explore the properties of this binary system.
文摘This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources all without previously known SiO detections. A tentative SiO emission was detected from the source IRAS18585+0900. The oxygen/carbonrichness of the circumstellar of IRAS18585+0900 is discussed with reference to its IRAS low resolution spectral (LRS) class 41. The low detection rate is discussed.
基金supported by the National Key Basic Research Program of China (973 program, No. 2014CB845700)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB01020300)the National Natural Science Foundation of China (Grant Nos. 11390371, 11222326 and 11233004)
文摘We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined red clump feature than the APOGEE dataset in the Teff versus log g diagram. With this advantage, we have separated red clump stars from red giant stars, and attempt to establish calibrations between the two datasets for the two groups of stars. The results show that there is a good consistency in temperature with a calibration close to the one-to-one line, and we can establish a satisfactory metallicity calibration of[Fe/H]APOGEE= 1.18[Fe/H]LAMOST ＋ 0.11 with a scatter of ～ 0.08 dex for both the red clump and red giant branch samples. For gravity, there is no correlation for red clump stars between the two datasets, and scatters around the calibrations of red giant stars are substantial. We found two main sources of scatter in log g for red giant stars. One is a group of stars with 0.00253 × Teff- 8.67 〈 log g 〈 2.6 located in the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with position in the Teff versus log g diagram. After excluding stars in these two regions,we have established two calibrations for red giant stars, log g APOGEE = 0.000615 ×Teff,LAMOST＋ 0.697 × log g LAMOST- 2.208（σ = 0.150） for [Fe/H] 〉-1 and log gAPOGEE= 0.000874×Teff,LAMOST＋0.588×log g LAMOST-3.117（σ = 0.167）for [Fe/H] 〈-1. The calibrations are valid for stars with Teff = 3800- 5400 K and log g = 0- 3.8 dex, and are useful in work aiming to combine the LAMOST and APOGEE datasets in a future study. In addition, we find that an SVM method based on asteroseismic log g is a good way to greatly improve the accuracy of gravity for these two regions, at least in the LAMOST dataset.
基金Supported by the National Natural Science Foundation of Chinasupported by Guizhou University (Grant No.2008036)+1 种基金the Guizhou Natural Science Foundation (Grant Nos.20092263 and 20104014)supported by the Joint Fund of Astronomy of the National Natural Science Foundation of China (Grant Nos.10978010 and 10963001)
文摘This paper presents new CCD BV RI light curves of the newly discovered RS CVn eclipsing binary V1034 Her in 2009 and 2010, the shapes of which are different from previously published results. They show an asymmetric outside eclipse, and we try to use a spot model to explain the phenomenon. Using the Wilson-Devinney program with a one-spot or two-spot model, photometric solutions of the system and starspot parameters were derived. Comparing the two results shows that the case of two spots is more successful in reproducing light-curve distortions. Looking at all the spot longitudes, the trend is towards active longitude belts and each active longitude belt may switch. Comparing the light curves from 2009 and 2010, we can see that the light curve changes over the long time scale of a year, especially in phase 0.25. In addition, we also collected the values of the maximum amplitudes of photometric distortion of the short-period RS CVn binary. We found for the first time that there is a trend of increasing activity with decreasing orbital period. Finally, fitting all available light minimum times including our newly obtained ones with a polynomial function confirmed that the orbital period of V1034 Her increased.
基金supported by the National Natural Science Foundation of China(Grant Nos.10373023 and 10773027)a grant from the Sik Sik Yuen of Hong Kong,China
文摘The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique, and find that the active regions shift oppositely along longitude on a time scale of one day. Combining with the observational data obtained by other groups, we discuss the evolution of spotted regions in the photosphere, and find that its starspots evolve not only on a short time scale but also on a long time scale. The pure chromospheric emissions for Ca IIHK and Hβ lines are derived by using the spectral subtraction technique. The variation of Ca IIHK lines＇ excess emission is spatially correlated to the starspot regions. There is no clear rotational modulation for the Hβ line＇s excess emission, probably due to the contamination of prominence emission.
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.
文摘By means of a population synthesis code, we investigate the Mira variables. Their birth rate （over 0.65yr^-1） and their number （～ 130000） in the Galaxy are estimated. For all possible Mira variables, ranges of their initial masses,pulsating periods, mass losses and lifetimes are given. We check our model with the observed Mira variables near the Sun and our results prove to be valid.
