In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between ...In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between which are the radiative inter- mediate layers with uneven chemical abundances. Semiconvection would occur in the intermediate layers between the convective core and the homogeneous envelope in massive stars. We treat core convective overshooting and semiconvection together as a process. We found that when decreasing overshooting, the semiconvection is more pronounced. In these two processes, we introduce one diffusive parameter D, which is different from other authors who have introduced different parameters for these two zones. The influences of the turbulent diffusion process on chemical evolution and other quantities of the stellar structure are shown in the present paper.展开更多
One-dimensional(1 D)model atmospheres are still the most commonly used tool for the determination of stellar chemical composition.Convection in the model is usually treated by mixing-length theory(MLT).The mixing-leng...One-dimensional(1 D)model atmospheres are still the most commonly used tool for the determination of stellar chemical composition.Convection in the model is usually treated by mixing-length theory(MLT).The mixing-length parameterαis generally calibrated from the Sun and applied to all other stars.The metal-poor giant,HD 122563,is an important benchmark star to test stellar atmosphere and interior physics.We investigate the influence of the convection mixing-length parameterαon the determination of chemical abundances of Na,Mg,Al,Si,Ca,Sc,Ti,Cr,Mn,Co,Ni,Sr,Y,Zr and Ba in the case of HD 122563,taking advantage of a high resolution and high signal-to-noise ratio HARPS spectrum.The abundance discrepanciesΔ[X/H]that occur due toαvariation rarely exceed 0.05 dex and most are less than 0.03 dex.We calculate the discrepancyΔ[X/H]using a line-by-line differential analysis.The abundance discrepancies do not have direct relation with either line strength or the excitation potential.For 1 D stellar atmospheric analysis of HD 122563,the accuracy of abundance determination does not strongly depend on the choice of mixing-length parameterα(causing average discrepancies of<0.03 dex),while the uncertainties in the effective temperature and surface gravity play a more important role.展开更多
Type II and Ib/c supernovae (SNe II and Ib/c) have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here w...Type II and Ib/c supernovae (SNe II and Ib/c) have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here with the help of recently developed numerical simulations of Galactic chemical evolution in the solar neighborhood to un- derstand the contributions of SNe II and Ib/c by comparing the stellar nucleosynthetic yields obtained by two leading groups in this field. These stellar nucleosynthetic yields differ in terms of their treatment of stellar evolution and nucleosynthesis. The formu- lation describing Galactic chemical evolution is developed with the recently revised solar metallicity of -0.014. Furthermore, the recent nucleosynthetic yields of stellar models based on the revised solar metallicity are also used. The analysis suggests that it could be difficult to explain, in a self-consistent manner, the various features asso- ciated with the elemental evolutionary trends over Galactic timescales by any single adopted stellar nucleosynthetic model that incorporates SNe II and Ib/c.展开更多
High resolution (R^40,000) and high signal-to-noise ratio (】150) spectra of two solar twins, HD146233 and HD195034, are obtained with the Coude Echelle Spectrograph at the 2.16 m telescope of the National Astronomica...High resolution (R^40,000) and high signal-to-noise ratio (】150) spectra of two solar twins, HD146233 and HD195034, are obtained with the Coude Echelle Spectrograph at the 2.16 m telescope of the National Astronomical Observatories of Chinese Academy of Sciences (Xinglong, China). Based on the detailed spectrum match, comparisons of chemical composition and chromospheric activity, HD146233 and HD195034 are confirmed that they are similar to the Sun except for lithium abundance, which is higher than the solar value. Moreover, among nine solar twin candidates (including HD146233 and HD195034) found in the previous works, we have picked out six good solar twin candidates based on newly-derived homogenous parameters, and collected their colors in the Johnson/Cousins, Tycho, 2MASS and Strmgren system from the literature. The average color are (B-V)⊙=0.644 mag, (V-Ic)⊙=0.707 mag, (BT-VT)⊙=0.725 mag, (J-H)⊙=0.288 mag, (H-K)⊙=0.066 mag, (v-y)⊙=1.028 mag, (v-b)⊙=0.619 mag, (u-v)⊙=0.954 mag and (b-y)⊙=0.409 mag, which represent the solar colors with higher precision than previous works.展开更多
基金co-sponsored by the National Natural Science Foundation of China (Grant Nos.11333006 and 10973035)the Chinese Academy of Sciences (Grant No.KJCX2-YW-T24)
文摘In massive stars, convection in the interior is different from that of inter- mediate and small mass stars. In the main-sequence phase of small mass stars, there is a convective core and a radiative envelope, between which are the radiative inter- mediate layers with uneven chemical abundances. Semiconvection would occur in the intermediate layers between the convective core and the homogeneous envelope in massive stars. We treat core convective overshooting and semiconvection together as a process. We found that when decreasing overshooting, the semiconvection is more pronounced. In these two processes, we introduce one diffusive parameter D, which is different from other authors who have introduced different parameters for these two zones. The influences of the turbulent diffusion process on chemical evolution and other quantities of the stellar structure are shown in the present paper.
基金the National Natural Science Foundation of China(Grant Nos.11988101,11890694,11773033)the National Key R&D Program of China(No.2019YFA0405502)。
文摘One-dimensional(1 D)model atmospheres are still the most commonly used tool for the determination of stellar chemical composition.Convection in the model is usually treated by mixing-length theory(MLT).The mixing-length parameterαis generally calibrated from the Sun and applied to all other stars.The metal-poor giant,HD 122563,is an important benchmark star to test stellar atmosphere and interior physics.We investigate the influence of the convection mixing-length parameterαon the determination of chemical abundances of Na,Mg,Al,Si,Ca,Sc,Ti,Cr,Mn,Co,Ni,Sr,Y,Zr and Ba in the case of HD 122563,taking advantage of a high resolution and high signal-to-noise ratio HARPS spectrum.The abundance discrepanciesΔ[X/H]that occur due toαvariation rarely exceed 0.05 dex and most are less than 0.03 dex.We calculate the discrepancyΔ[X/H]using a line-by-line differential analysis.The abundance discrepancies do not have direct relation with either line strength or the excitation potential.For 1 D stellar atmospheric analysis of HD 122563,the accuracy of abundance determination does not strongly depend on the choice of mixing-length parameterα(causing average discrepancies of<0.03 dex),while the uncertainties in the effective temperature and surface gravity play a more important role.
文摘Type II and Ib/c supernovae (SNe II and Ib/c) have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here with the help of recently developed numerical simulations of Galactic chemical evolution in the solar neighborhood to un- derstand the contributions of SNe II and Ib/c by comparing the stellar nucleosynthetic yields obtained by two leading groups in this field. These stellar nucleosynthetic yields differ in terms of their treatment of stellar evolution and nucleosynthesis. The formu- lation describing Galactic chemical evolution is developed with the recently revised solar metallicity of -0.014. Furthermore, the recent nucleosynthetic yields of stellar models based on the revised solar metallicity are also used. The analysis suggests that it could be difficult to explain, in a self-consistent manner, the various features asso- ciated with the elemental evolutionary trends over Galactic timescales by any single adopted stellar nucleosynthetic model that incorporates SNe II and Ib/c.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10821061 and 10673015)the National Basic Research Program of China (Grant No. 2007CB815103/815403)the National High Technology Research and Development Program of China (Grant No. 2006AA01A120)
文摘High resolution (R^40,000) and high signal-to-noise ratio (】150) spectra of two solar twins, HD146233 and HD195034, are obtained with the Coude Echelle Spectrograph at the 2.16 m telescope of the National Astronomical Observatories of Chinese Academy of Sciences (Xinglong, China). Based on the detailed spectrum match, comparisons of chemical composition and chromospheric activity, HD146233 and HD195034 are confirmed that they are similar to the Sun except for lithium abundance, which is higher than the solar value. Moreover, among nine solar twin candidates (including HD146233 and HD195034) found in the previous works, we have picked out six good solar twin candidates based on newly-derived homogenous parameters, and collected their colors in the Johnson/Cousins, Tycho, 2MASS and Strmgren system from the literature. The average color are (B-V)⊙=0.644 mag, (V-Ic)⊙=0.707 mag, (BT-VT)⊙=0.725 mag, (J-H)⊙=0.288 mag, (H-K)⊙=0.066 mag, (v-y)⊙=1.028 mag, (v-b)⊙=0.619 mag, (u-v)⊙=0.954 mag and (b-y)⊙=0.409 mag, which represent the solar colors with higher precision than previous works.