We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM ...We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent- heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.展开更多
The effect of tidal torques on rotational mixing in close binaries is investigated. It is found that spin angular momentum can attain a high value due to a strong tidal torque. Nitrogen and helium enrichment occurs ea...The effect of tidal torques on rotational mixing in close binaries is investigated. It is found that spin angular momentum can attain a high value due to a strong tidal torque. Nitrogen and helium enrichment occurs early in the binary system that is triggered by tides. The stellar radius can reach a high value in the single star model with high initial velocities at the early stage of the evolution, but efficient rotational mixing can inhibit stellar expanding at the subsequent evolution. Central compactness is increased by the centrifugal force at the early stage of evolution but is reduced by rotational mixing induced by strong tides. The binary models with weak tides have high values of central temperature and stellar radius. Rotational mixing in single stars can slow down the shrinkage of convective cores, while convective cores can be expanded by strong tides in the binary system.Efficient rotational mixing induced by tides can cause the star to evolve towards high temperature and luminosity.展开更多
Understanding rotation,which has been identified as a very important factor in physics,is necessary in order to understand the evolution of massive stars[1,2].Rotation can drive mixing processes of chemical elements i...Understanding rotation,which has been identified as a very important factor in physics,is necessary in order to understand the evolution of massive stars[1,2].Rotation can drive mixing processes of chemical elements in the stellar interior[3-5].Nitrogen,a better tracer for rotational mixing during main sequence evolution,is produced in the hot interior layers by carbon conversion via CN-cycling on a very short time scale.On a longer time scale(about 1-2 Myr in the center of a 20M_⊙star)the CNO cycle comes into equilibrium,which leads to additional N at the expense of both carbon and oxygen.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11463002the Open Foundation of Key Laboratory for the Structure and Evolution of Celestial Objects of Chinese Academy of Sciences under Grant No OP201405the Western Project of State Scholarship Foundation by the China Scholarship Council
文摘We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent- heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.
基金Supported by the National Natural Science Foundation of China under Grant No 11463002the Open Foundation of key Laboratory for the Structure and evolution of Celestial Objects of Chinese Academy of Sciences under Grant No OP201405
文摘The effect of tidal torques on rotational mixing in close binaries is investigated. It is found that spin angular momentum can attain a high value due to a strong tidal torque. Nitrogen and helium enrichment occurs early in the binary system that is triggered by tides. The stellar radius can reach a high value in the single star model with high initial velocities at the early stage of the evolution, but efficient rotational mixing can inhibit stellar expanding at the subsequent evolution. Central compactness is increased by the centrifugal force at the early stage of evolution but is reduced by rotational mixing induced by strong tides. The binary models with weak tides have high values of central temperature and stellar radius. Rotational mixing in single stars can slow down the shrinkage of convective cores, while convective cores can be expanded by strong tides in the binary system.Efficient rotational mixing induced by tides can cause the star to evolve towards high temperature and luminosity.
基金supported by the National Natural Science Foundation of China(Grant No.11463002)the Open Foundation of the Key Laboratory for the Structure,and Evolution of Celestial Objects,Chinese Academy of Sciences(Grant No.OP201405)
文摘Understanding rotation,which has been identified as a very important factor in physics,is necessary in order to understand the evolution of massive stars[1,2].Rotation can drive mixing processes of chemical elements in the stellar interior[3-5].Nitrogen,a better tracer for rotational mixing during main sequence evolution,is produced in the hot interior layers by carbon conversion via CN-cycling on a very short time scale.On a longer time scale(about 1-2 Myr in the center of a 20M_⊙star)the CNO cycle comes into equilibrium,which leads to additional N at the expense of both carbon and oxygen.
