We investigate the relationships between infrared excess(IRX = LIR/LUV) and Balmer decrement(Hα/Hβ) as indicators of dust attenuation for 609 H II regions at scales of ~50–200 pc in NGC 628, utilizing data from Ast...We investigate the relationships between infrared excess(IRX = LIR/LUV) and Balmer decrement(Hα/Hβ) as indicators of dust attenuation for 609 H II regions at scales of ~50–200 pc in NGC 628, utilizing data from AstroSat, the James Webb Space Telescope(JWST) and Multi Unit Spectroscopic Explorer. Our findings indicate that about three-fifths of the sample H II regions reside within the regime occupied by local star-forming galaxies(SFGs) along the dust attenuation correlation described by their corresponding color excess parameters E(B-V)IRX= 0.51 E(B-V)Hα/Hβ. Nearly 27% of the sample exhibits E(B-V)IRX> E(B-V)Hα/Hβ, while a small fraction(~13%) displays significantly lower E(B-V)IRXcompared to E(B-V)Hα/Hβ. These results suggest that the correlation between the two dust attenuation indicators no longer holds for spatially resolved H II regions. Furthermore, the ratio of E(B-V)IRXto E(B-V)Hα/Hβremains unaffected by various physical parameters of the H II regions, including star formation rate(SFR), SFR surface density, infrared luminosity(LIR),LIRsurface density, stellar mass, gas-phase metallicity, circularized radius, and the distance to the galactic center.We argue that the ratio is primarily influenced by the evolution of the surrounding interstellar medium of the starforming regions, transitioning from an early dense and thick phase to the late blown-away stage.展开更多
The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because rec...The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because recent results seem also to show that these stars are distributed across the regions least affected by interstellar absorption and reproduce the observed composite star field density map, we carried out a detailed spectroscopic analysis of a number of chemical element abundances of tidal tail star candidates in order to investigate the relationship between them and NGC 6362. From European Southern Observatory's VLT@FLAMES spectra we found that the red giant branch stars selected as the cluster's tidal tail stars neither have overall metallicities nor abundances of Mg, Ca, Sc, Ti, Cr, Ni and Ba similar to the cluster's ones. Moreover, they are mainly alike to stars that belong to the Milky Way thick disk, some of them could be part of the thin disk and a minor percentage could belong to the Milky Way halo star population. On the other hand, since the resulting radial velocities do not exhibit a distribution function similar to that of the cluster's stars, we concluded that looking for kinematic properties similar to those of the cluster would not seem to be as suitable of an approach for selecting the cluster's tidal tail stars as previously thought.展开更多
In this paper,~12 yr long-term Pass 8 data from Fermi Large Area Telescope for the 157 globular clusters are carefully re-analyzed.Besides the 31 globular clusters reported in the fourth Fermi Large Area Telescope cat...In this paper,~12 yr long-term Pass 8 data from Fermi Large Area Telescope for the 157 globular clusters are carefully re-analyzed.Besides the 31 globular clusters reported in the fourth Fermi Large Area Telescope catalog Data Release 2,NGC 1851 is identified as a gamma-ray emitter and the significant gamma-ray emissions from NGC 6715 and NGC 6723 are detected.Especially NGC 6715 is located at a distance of 26.8 kpc,so far it is the farthest globular cluster detected in gamma-rays.A detailed analysis for these three globular clusters has been performed,but their gamma-ray pulsation emissions or flux variabilities are not found.The numbers of millisecond pulsars(MSPs)in these globular clusters are estimated under the assumption that each MSP inside globular clusters emits a similar amount of gamma-rays.Some possible origins of gamma-ray emission from globular clusters,such as MSPs,pulsar binary systems and/or dark matter,are discussed.展开更多
利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带...利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带来的影响,在数据预处理阶段将3个分量的数据统一标准化至[0,1]区间.利用第k个最近邻点距离方法分析了1046颗恒星样本在标准化无量纲3D速度空间的分布特征,再根据第k个最近邻点距离随k值的变化趋势确定了DBSCAN聚类算法的输入参数(Eps,MinPts),最后利用DBSCAN聚类算法分离出497颗3D运动学成员星.分析结果表明得到的3D运动学成员星是可靠的.展开更多
基金supported by the National Key Research and Development Program of China (2023YFA1608100)the National Science Foundation of China (NSFC, Grant Nos.12233005, 12073078, 12173088, and 12303015)+3 种基金the China Manned Space Program with grants nos. CMS-CSST-2025-A20 and CMS-CSST-2025-A08the support from the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology(2024yjrc104)the National Science Foundation of Jiangsu Province (BK20231106)the science research grants from the China Manned Space Project
文摘We investigate the relationships between infrared excess(IRX = LIR/LUV) and Balmer decrement(Hα/Hβ) as indicators of dust attenuation for 609 H II regions at scales of ~50–200 pc in NGC 628, utilizing data from AstroSat, the James Webb Space Telescope(JWST) and Multi Unit Spectroscopic Explorer. Our findings indicate that about three-fifths of the sample H II regions reside within the regime occupied by local star-forming galaxies(SFGs) along the dust attenuation correlation described by their corresponding color excess parameters E(B-V)IRX= 0.51 E(B-V)Hα/Hβ. Nearly 27% of the sample exhibits E(B-V)IRX> E(B-V)Hα/Hβ, while a small fraction(~13%) displays significantly lower E(B-V)IRXcompared to E(B-V)Hα/Hβ. These results suggest that the correlation between the two dust attenuation indicators no longer holds for spatially resolved H II regions. Furthermore, the ratio of E(B-V)IRXto E(B-V)Hα/Hβremains unaffected by various physical parameters of the H II regions, including star formation rate(SFR), SFR surface density, infrared luminosity(LIR),LIRsurface density, stellar mass, gas-phase metallicity, circularized radius, and the distance to the galactic center.We argue that the ratio is primarily influenced by the evolution of the surrounding interstellar medium of the starforming regions, transitioning from an early dense and thick phase to the late blown-away stage.
基金Based on observations collected at the European Southern Observatory under ESO program(s)113.2661.001.
文摘The inner Milky Way disk globular cluster NGC 6362 appears to exhibit tidal tails composed of stars that have proper motions and positions in the color–magnitude diagram similar to those of cluster stars. Because recent results seem also to show that these stars are distributed across the regions least affected by interstellar absorption and reproduce the observed composite star field density map, we carried out a detailed spectroscopic analysis of a number of chemical element abundances of tidal tail star candidates in order to investigate the relationship between them and NGC 6362. From European Southern Observatory's VLT@FLAMES spectra we found that the red giant branch stars selected as the cluster's tidal tail stars neither have overall metallicities nor abundances of Mg, Ca, Sc, Ti, Cr, Ni and Ba similar to the cluster's ones. Moreover, they are mainly alike to stars that belong to the Milky Way thick disk, some of them could be part of the thin disk and a minor percentage could belong to the Milky Way halo star population. On the other hand, since the resulting radial velocities do not exhibit a distribution function similar to that of the cluster's stars, we concluded that looking for kinematic properties similar to those of the cluster would not seem to be as suitable of an approach for selecting the cluster's tidal tail stars as previously thought.
基金supported in part by the National Key R&D Program of China under Grant No.2018YFA0404204the National Natural Science Foundation of China Nos.12163006 and 12233006+1 种基金the Basic Research Program of Yunnan Province No.202201AT070137the joint foundation of Department of Science and Technology of Yunnan Province and Yunnan University No.202201BF070001-020。
文摘In this paper,~12 yr long-term Pass 8 data from Fermi Large Area Telescope for the 157 globular clusters are carefully re-analyzed.Besides the 31 globular clusters reported in the fourth Fermi Large Area Telescope catalog Data Release 2,NGC 1851 is identified as a gamma-ray emitter and the significant gamma-ray emissions from NGC 6715 and NGC 6723 are detected.Especially NGC 6715 is located at a distance of 26.8 kpc,so far it is the farthest globular cluster detected in gamma-rays.A detailed analysis for these three globular clusters has been performed,but their gamma-ray pulsation emissions or flux variabilities are not found.The numbers of millisecond pulsars(MSPs)in these globular clusters are estimated under the assumption that each MSP inside globular clusters emits a similar amount of gamma-rays.Some possible origins of gamma-ray emission from globular clusters,such as MSPs,pulsar binary systems and/or dark matter,are discussed.
文摘利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带来的影响,在数据预处理阶段将3个分量的数据统一标准化至[0,1]区间.利用第k个最近邻点距离方法分析了1046颗恒星样本在标准化无量纲3D速度空间的分布特征,再根据第k个最近邻点距离随k值的变化趋势确定了DBSCAN聚类算法的输入参数(Eps,MinPts),最后利用DBSCAN聚类算法分离出497颗3D运动学成员星.分析结果表明得到的3D运动学成员星是可靠的.
