We report the discovery of an extremely metal-poor（EMP） giant,LAMOST J110901.22＋075441.8, which exhibits a large excess of r-process elements with [Eu/Fe] ～ ＋1.16. The star is one of the newly discovered EMP star...We report the discovery of an extremely metal-poor（EMP） giant,LAMOST J110901.22＋075441.8, which exhibits a large excess of r-process elements with [Eu/Fe] ～ ＋1.16. The star is one of the newly discovered EMP stars identified from the LAMOST low-resolution spectroscopic survey and a highresolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22＋075441.8. The abundance pattern of LAMOST J110901.22＋075441.8 in the range of C through Zn is in line with the ＂normal＂ population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22＋075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy match the scaled solar r-process pattern well.LAMOST J110901.22＋075441.8 provides the first detailed measurements of neutroncapture elements among r-II stars at such low metallicity with [Fe/H]-3.4, and exhibits similar behavior as other r-II stars in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu.展开更多
The East Asian Very Long Baseline Interferometry(VLBI) Network(EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China,Japan and Korea.EAVN aims at forming a joi...The East Asian Very Long Baseline Interferometry(VLBI) Network(EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China,Japan and Korea.EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions.After the combination of the Korean VLBI Network(KVN) and the VLBI Exploration of Radio Astrometry(VERA) into Ka VA,further expansion with the joint array in East Asia is actively promoted.Here we report the first imaging results(at 22 and 43 GHz) of bright radio sources obtained with Ka VA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China.To test the EAVN imaging performance for different sources,we observed four active galactic nuclei(AGN) having different brightness and morphology.As a result,we confirmed that the Tianma 65-m Radio Telescope(TMRT) significantly enhances the overall array sensitivity,a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of Ka VA only.The addition of the Nanshan 26-m Radio Telescope(NSRT) further doubled the east-west angular resolution.With the resulting high-dynamic-range,high-resolution images with EAVN(Ka VA+TMRT+NSRT),various fine-scale structures in our targets,such as the counter-jet in M87,a kink-like morphology of the 3 C 273 jet and the weak emission in other sources are successfully detected.This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general.Ongoing expansion of EAVN will further enhance the angular resolution,detection sensitivity and frequency coverage of the network.展开更多
A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light fr...A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.展开更多
Lithium is an ancient element that was first produced by the Big Bang Nucleosynthesis(BBN)a few minutes after the birth of the Universe.Lithium is a sensitive tracer for a number of processes in a variety of astrophys...Lithium is an ancient element that was first produced by the Big Bang Nucleosynthesis(BBN)a few minutes after the birth of the Universe.Lithium is a sensitive tracer for a number of processes in a variety of astrophysical environments due to its multi-channels of production and fragility.These features also make lithium a complex element at the center of many unsolved problems.The behavior of lithium in the low-mass evolved stars is one such issue.It is known that such stars not only destroy but also produce lithium,while neither the destruction details nor the production mechanisms over different evolutionary phases are clear.In this paper,we summarize the recent results obtained from the studies combining large-scale spectroscopic surveys,asteroseismology,and traditional high-resolution spectroscopy.We present the detailed evolution behaviors from the red giant branch(RGB)to the red clump(RC)phase characterized by the core helium-burning in the stellar interior.We show the new signatures discovered from the recent studies for the lithium-enhanced giants and also discuss various observational and theoretical constraints on lithium production in red clump stars.展开更多
基金the paper.H.N.L.and G.Z.acknowledge supports by the National Natural Science Foundation of China (Grant Nos.11103030, 11233004 and 11390371)W.A.and T.S.are supported by the JSPS Grant-in-Aid for Scientific Research (S: 23224004)+1 种基金S.H.is supported by the JSPS Grant-in-Aid for Scientific Research (c:26400231)N.C.acknowledges support from Sonderforschungsbereich 881 "The Milky Way System" (subproject A4) of the German Research Foundation (DFG)
文摘We report the discovery of an extremely metal-poor（EMP） giant,LAMOST J110901.22＋075441.8, which exhibits a large excess of r-process elements with [Eu/Fe] ～ ＋1.16. The star is one of the newly discovered EMP stars identified from the LAMOST low-resolution spectroscopic survey and a highresolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22＋075441.8. The abundance pattern of LAMOST J110901.22＋075441.8 in the range of C through Zn is in line with the ＂normal＂ population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22＋075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy match the scaled solar r-process pattern well.LAMOST J110901.22＋075441.8 provides the first detailed measurements of neutroncapture elements among r-II stars at such low metallicity with [Fe/H]-3.4, and exhibits similar behavior as other r-II stars in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu.
基金supported by The Graduate University for Advanced Studies (SOKENDAI)supported by the Japanese Government (MEXT) Scholarship+18 种基金supported by JSPS KAKENHI Grant Numbers JP18K03656 (M.K.),JP18H03721 (K.N.,K.H.and M.K.),JP19H01943 (K.H.,F.T.and Y.H.) and JP18KK0090 (K.H.and F.T.)supported by the Mitsubishi Foundation (grant number 201911019)supported by an EACOA Fellowship awarded by the East Asia Core Observatories Association,which consists of the Academia Sinica Institute of Astronomy and Astrophysics,the National Astronomical Observatory of Japan,the Center for Astronomical Mega-Science,the Chinese Academy of Sciencesthe Korea Astronomy and Space Science Institutethe financial support from the National Research Foundation (NRF) of Korea via Global Ph.D.Fellowship Grant 2014H1A2A1018695 and 2015H1A2A1033752,respectivelysupport from the NRF via Grant 2019R1F1A1059721supported by the Major Program of the National Natural Science Foundation of China (NSFC,Grant Nos.11590780 and 11590784)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.KJCX1-YW-18)the Scientific Program of Shanghai Municipality (08DZ1160100)Key Laboratory for Radio Astronomy,CASsupport from NSFC (Grant No.11803071)supported by the National Key R&D Program of China (Grant No.2018YFA0404602)the CAS ‘Light of West China’ Program (Grant No.2018-XBQNXZ-B021)the NSFC (Grant Nos.U2031212 and 61931002)the Youth Innovation Promotion Association of the CAS (Grant No.2017084)support from Fundamental Research Grant Scheme (FRGS) FRGS/1/2019/STG02/UM/02/6supported by the Max Planck Partner Group of the MPG and the CASthe support by the Key Program of the NSFC (Grant No.11933007)the Research Program of Fundamental and Frontier Sciences,CAS (Grant No.ZDBS-LY-SLH011)。
文摘The East Asian Very Long Baseline Interferometry(VLBI) Network(EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China,Japan and Korea.EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions.After the combination of the Korean VLBI Network(KVN) and the VLBI Exploration of Radio Astrometry(VERA) into Ka VA,further expansion with the joint array in East Asia is actively promoted.Here we report the first imaging results(at 22 and 43 GHz) of bright radio sources obtained with Ka VA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China.To test the EAVN imaging performance for different sources,we observed four active galactic nuclei(AGN) having different brightness and morphology.As a result,we confirmed that the Tianma 65-m Radio Telescope(TMRT) significantly enhances the overall array sensitivity,a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of Ka VA only.The addition of the Nanshan 26-m Radio Telescope(NSRT) further doubled the east-west angular resolution.With the resulting high-dynamic-range,high-resolution images with EAVN(Ka VA+TMRT+NSRT),various fine-scale structures in our targets,such as the counter-jet in M87,a kink-like morphology of the 3 C 273 jet and the weak emission in other sources are successfully detected.This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general.Ongoing expansion of EAVN will further enhance the angular resolution,detection sensitivity and frequency coverage of the network.
基金supported by a Grant-in-Aid for Scientific Research (No. 24540231)supported by the U.S. National Science Foundation under Award (No. 1009203)
文摘A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.
基金This work is supported by the National Natural Science Foundation of China(11988101,12090040,12090044,12022304,11833006,11973052,11973049,11890694,and U2031203)the National Key R&D Program of China(2019YFA0405502)+6 种基金support of the JSPS-CAS Joint Research Program.H.-L.Y.and H.L.acknowledge support from the Youth Innovation Promotion Association of the CAS(id.2019060 and Y202017,respectively)NAOC Nebula Talents Program.J.-H.Z.acknowledges support from NSFC(12103063)from China Postdoctoral Science Foundation funded project(2020M680672)Y.B.K acknowledges the support of the NSFC(11850410437)H.L.acknowledges support from the Strategic Priority Research Program of Chinese Academy of Sciences,(XDB34020205)Guoshoujing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST)is a National Major Scientific Project built by the Chinese Academy of Sciences.Funding for the project has been provided by the National Development and Reform CommissionLAMOST is operated and managed by the National Astronomical Observatories,Chinese Academy of Sciences.
文摘Lithium is an ancient element that was first produced by the Big Bang Nucleosynthesis(BBN)a few minutes after the birth of the Universe.Lithium is a sensitive tracer for a number of processes in a variety of astrophysical environments due to its multi-channels of production and fragility.These features also make lithium a complex element at the center of many unsolved problems.The behavior of lithium in the low-mass evolved stars is one such issue.It is known that such stars not only destroy but also produce lithium,while neither the destruction details nor the production mechanisms over different evolutionary phases are clear.In this paper,we summarize the recent results obtained from the studies combining large-scale spectroscopic surveys,asteroseismology,and traditional high-resolution spectroscopy.We present the detailed evolution behaviors from the red giant branch(RGB)to the red clump(RC)phase characterized by the core helium-burning in the stellar interior.We show the new signatures discovered from the recent studies for the lithium-enhanced giants and also discuss various observational and theoretical constraints on lithium production in red clump stars.
