We report on the first investigation into kinematics and chromospheric activity of M dwarfs from the Guo Shou Jing Telescope （also called the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST） data ...We report on the first investigation into kinematics and chromospheric activity of M dwarfs from the Guo Shou Jing Telescope （also called the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST） data release one （DR1）. The sample comprises 71 304 M dwarfs. Their fundamental parameters such as spectral types, radial velocities, important molecular band indices and magnetic activities are measured. Their distances are determined by a spectroscopic parallax relation. Space motion （U, V, W） and Galactocentric cylindrical coordinates （R, θ, Z） for the M dwarfs are also computed. We examine velocity dispersion as a function of height from the Galactic plane and find that all three components of velocity dispersion in- crease with height as measured with respect to the Galactic plane. The investigation into chromospheric activities along the height from the Galactic plane confirms that M dwarfs closer to the Galactic plane are more likely to be active. We take a pure kinematical approach to select thin disk stars and thick disk stars from our sample, then to investigate the differences in properties between these two populations. Our analysis is in excellent agreement with previous studies and leads to a better understanding of the structure of the Galactic disk.展开更多
基于COSMOS(Cosmic Evolution Survey)天区的多波段测光数据和HST(Hubble Space Telescope)近红外高分辨率观测图像,利用质量限(恒星质量M*≥1010.5M⊙)选取了362个红移分布在1≤z≤3的星系样本,并对这些大质量星系的形态特征进行了分...基于COSMOS(Cosmic Evolution Survey)天区的多波段测光数据和HST(Hubble Space Telescope)近红外高分辨率观测图像,利用质量限(恒星质量M*≥1010.5M⊙)选取了362个红移分布在1≤z≤3的星系样本,并对这些大质量星系的形态特征进行了分类研究.来自UVJ(U-V和V-J)双色图分类系统、目视分类系统、非模型化分类系统(基尼系数G和矩指数M20)和模型化分类系统(S′ersic index,n)的分类结果彼此相一致.相比较于恒星形成星系(SFGs),通过UVJ双色图定义的宁静星系(QGs)表现出致密的椭圆结构,而且G和n值偏大,但M20和星系有效半径(re)偏小.不同星系分类系统(双色图分类系统、非模型化分类系统和模型化分类系统)定义的SFGs和QGs样本,都明显存在星系的大小随红移的演化关系,这种演化趋势QGs比SFGs更剧烈,而且不依赖于星系分类方法的选择.展开更多
Employing recent TP-AGB synthesis, we have carried out a detailed study of Mira variables by means of a population synthesis code. We estimate that the total number of Mira variables in the Galaxy is from about 100 00...Employing recent TP-AGB synthesis, we have carried out a detailed study of Mira variables by means of a population synthesis code. We estimate that the total number of Mira variables in the Galaxy is from about 100 000 to 600 000 and their average lifetimes are between about 150 000 and 830 000 yr. The ratio of the number of O-Mira variables to that of C-Mira variables ranges from about 0.68 to 6.2. The effects of input physical parameters （mass loss rate, the minimum core mass for the third dredge-up, the third dredge-up efficiency and theoretical criterion for selecting Mira variables） on the Mira population are discussed.展开更多
Since Baade＇s photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our invest...Since Baade＇s photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope （HST） based stellar population studies which have resolved red-giant branch （RGB） and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32＇s anomalously high central velocity dispersion for a dwarf galaxy （several times that of either NGC 147, NGC 185 or NGC 205） or existing planetary nebula observations （which suggest that M32 is more than twice as distant as M31） and also requires an elaborate physical explanation for M32＇s inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by： （1） a central velocity dispersion typical of intermediate galaxies, （2） the published planetary nebula observations, and （3） known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary.This suggests that current understanding of some relevant fields is still very far from adequate.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
We report a possible dipole anisotropy in acceleration scale g↑ with 147 rotationally supported galaxies in the local Universe. It is found that a monopole and dipole correction for the radial acceleration relation c...We report a possible dipole anisotropy in acceleration scale g↑ with 147 rotationally supported galaxies in the local Universe. It is found that a monopole and dipole correction for the radial acceleration relation can better describe the SPARC data set. The monopole term is negligible but the dipole magnitude is significant. It is also found that the dipole correction is mostly induced by anisotropy in the acceleration scale. The magnitude of the g↑-dipole reaches 0.25±0.04, and its direction is aligned to （l,b）=（171.30°±7.18°,-15.41°±4.87°）, which is very close to the maximum anisotropy direction from the hemisphere comparison method. Furthermore, a robust check shows that the dipole anisotropy could not be reproduced by an isotropic mock data set. However, it is still premature to claim that the Universe is anisotropic, due to the small data samples and uncertainty in the current observations.展开更多
基金Supported by the National Natural Science Foundation of China
文摘We report on the first investigation into kinematics and chromospheric activity of M dwarfs from the Guo Shou Jing Telescope （also called the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST） data release one （DR1）. The sample comprises 71 304 M dwarfs. Their fundamental parameters such as spectral types, radial velocities, important molecular band indices and magnetic activities are measured. Their distances are determined by a spectroscopic parallax relation. Space motion （U, V, W） and Galactocentric cylindrical coordinates （R, θ, Z） for the M dwarfs are also computed. We examine velocity dispersion as a function of height from the Galactic plane and find that all three components of velocity dispersion in- crease with height as measured with respect to the Galactic plane. The investigation into chromospheric activities along the height from the Galactic plane confirms that M dwarfs closer to the Galactic plane are more likely to be active. We take a pure kinematical approach to select thin disk stars and thick disk stars from our sample, then to investigate the differences in properties between these two populations. Our analysis is in excellent agreement with previous studies and leads to a better understanding of the structure of the Galactic disk.
基金funded by the National Natural Science Foundation of China(NSFC) under Nos. 10763001 and 10647003the Natural Science Foundation of Xinjiang underNo. 2009211B01the Scientific Research Program of the Higher Education Institution of Xinjiangunder No. XJEDU2008S12
文摘Employing recent TP-AGB synthesis, we have carried out a detailed study of Mira variables by means of a population synthesis code. We estimate that the total number of Mira variables in the Galaxy is from about 100 000 to 600 000 and their average lifetimes are between about 150 000 and 830 000 yr. The ratio of the number of O-Mira variables to that of C-Mira variables ranges from about 0.68 to 6.2. The effects of input physical parameters （mass loss rate, the minimum core mass for the third dredge-up, the third dredge-up efficiency and theoretical criterion for selecting Mira variables） on the Mira population are discussed.
文摘Since Baade＇s photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope （HST） based stellar population studies which have resolved red-giant branch （RGB） and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32＇s anomalously high central velocity dispersion for a dwarf galaxy （several times that of either NGC 147, NGC 185 or NGC 205） or existing planetary nebula observations （which suggest that M32 is more than twice as distant as M31） and also requires an elaborate physical explanation for M32＇s inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by： （1） a central velocity dispersion typical of intermediate galaxies, （2） the published planetary nebula observations, and （3） known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary.This suggests that current understanding of some relevant fields is still very far from adequate.
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Supported by National Natural Science Foundation of China(11675182,11690022,11603005)
文摘We report a possible dipole anisotropy in acceleration scale g↑ with 147 rotationally supported galaxies in the local Universe. It is found that a monopole and dipole correction for the radial acceleration relation can better describe the SPARC data set. The monopole term is negligible but the dipole magnitude is significant. It is also found that the dipole correction is mostly induced by anisotropy in the acceleration scale. The magnitude of the g↑-dipole reaches 0.25±0.04, and its direction is aligned to （l,b）=（171.30°±7.18°,-15.41°±4.87°）, which is very close to the maximum anisotropy direction from the hemisphere comparison method. Furthermore, a robust check shows that the dipole anisotropy could not be reproduced by an isotropic mock data set. However, it is still premature to claim that the Universe is anisotropic, due to the small data samples and uncertainty in the current observations.
