分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We systematically searched for open clusters in the solar neighborhood within 500 pc using pyUPMASK and HDBSCAN clustering algorithms based on {\it Gaia} DR3. Taking into consideration that the physical size for most open clusters is less than 50 pc, we adopted a slicing approach for different distance shells and identified 324 neighboring open clusters, including 223 reported open clusters and 101 newly discovered open clusters (named as OCSN, Open Cluster of Solar Neighborhood). Our discovery has increased the number of open clusters in the solar neighborhood by about 45\%. In this work, larger spatial extents and more member stars were attained for our cluster sample. We provided the member stars and the membership probabilities through the pyUPMASK algorithm for each cluster and derived their astrophysical, age, and structural parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： With the help of Gaia data, it is noted that in addition to the core components, there are low-density outer halo components in the extended region of open clusters. To study the extended structure beyond the core radius of the cluster ($\sim$ 10 pc), based on Gaia EDR3 data, taking up to 50 pc as the searching radius, we use the pyUPMASK algorithm to re-determine the member stars of the open cluster within 1-2 kpc. We obtain the member stars of 256 open clusters, especially those located in the outer halo region of open clusters. Furthermore, we find that most open clusters' radial density profile in the outer region deviates from the King's profile. To better describe the internal and external structural characteristics of open clusters, we propose a double components model for description: core components with King model distribution and outer halo components with logarithmic Gaussian distribution, and then suggest using four radii ( $r_c$, $r_t$, $r_o$, $r_e$) for describing the structure and distribution profile of star clusters, where $r_t$ and $r_e$ represent the boundaries of core components and outer halo components respectively. Finally, we provide a catalog of 256 clusters with structural parameters. In addition, our study shows the sizes of these radii are statistically linear related, which indicates that the inner and outer regions of the cluster are interrelated and follow similar evolutionary processes. Further, we show that the structure of two components can be used to better trace the cluster evolution properties in different stages.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： COIN-Gaia 13 is a newly discovered open cluster revealed by Gaia DR2 data. It is a nearby open cluster with a distance of about 513 pc. Combined with the five-dimensional astrometric data of Gaia EDR3 with higher accuracy, we use the membership assignment algorithm (pyUPMASK) to determine the membership of COIN-Gaia 13 in a large extended spatial region. The cluster has found 478 candidate members. After obtaining reliable cluster members, we further study its basic properties and spatial distribution. Our results show that there is an obvious extended structure of the cluster in the X-Y plane. This elongated structure is distributed along the spiral arm, and the whole length is about 270 pc. The cluster age is 250 Myr, the total mass is about 439 M$_\odot$, and the tidal radius of the cluster is about 11 pc. Since more than half of the member stars (352 stars) are located outside twice the tidal radius, it is suspected that this cluster is undergoing the dynamic dissolution process. Furthermore, the spatial distribution and kinematic analysis indicate that the extended structure in COIN-Gaia 13 is more likely to be caused by the differential rotation of the Galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We report 541 new open cluster candidates in Gaia EDR3 through revisiting the cluster results from an earlier analysis of the Gaia DR2, which revealed nearly a thousand open cluster candidates in the solar neighborhood (mostly d < 3 kpc) resideing at Galactic latitudes |b| < 20 degrees. A subsequent comparison with lists of known clusters shows a large increases of the cluster samples within 2 kpc from the Sun. We assign membership probabilities to the stars through the open source pyUPMASK algorithm, and also estimate the physical parameters through isochrone fitting for each candidate. Most of the new candidates show small total proper motion dispersions and clear features in the color-magnitude diagrams. Besides, the metallicity gradient of the new candidates is consistent with those found in the literature. The cluster parameters and member stars are available at CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via https://cdsarc.unistra.fr/viz-bin/cat/J/ApJS. The discovery of these new objects shows that the open cluster samples in Gaia data is still not complete, and more discoveries are expected in the future researches.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Chenyu He
Weijia Sun
Chengyuan Li
Lu Li
Zhengyi Shao
Jing Zhong
Li Chen
Richard de Grijs
Baitian Tang
Songmei Qin
Zara Randriamanakoto
摘要： In addition to the extended main-sequence turnoffs widely found in young and intermediate-age (~ 600 Myr-2 Gyr-old) star clusters, some younger clusters even exhibit split main sequences (MSs). Different stellar rotation rates are proposed to account for the bifurcated MS pattern, with red and blue MSs (rMS and bMS) populated by fast and slowly rotating stars, respectively. Using photometry from Gaia Early Data Release 3, we report a Galactic open cluster with a bifurcated MS, NGC 2422 ( ~ 90 Myr). We exclude the possibilities that the bifurcated MS pattern is caused by photometric noise or differential reddening. We aim to examine if stellar rotation can account for the split MSs. We use spectra observed with the Canada-France-Hawaii Telescope and the Southern African Large Telescope, and directly measured v sin i, the projected rotational velocities, for stars populating the bMS and rMS. We find that their v sin i values are weakly correlated with their loci in the color-magnitude diagram because of contamination caused by a large fraction of rMS stars with low projected rotational velocities. Based on the spectral energy distribution fitting method, we suggest that these slowly rotating stars at the rMS may hide a binary companion, which breaks the expected v sin i-color correlation. Future time-domain studies focusing on whether these slowly rotating stars are radial velocity variables are crucial to test the roles of stellar rotation and binarity in generating the split MSs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We systematically searched for open clusters in the solar neighborhood within 500 pc using pyUPMASK and HDBSCAN clustering algorithms based on {\it Gaia} DR3. Taking into consideration that the physical size for most open clusters is less than 50 pc, we adopted a slicing approach for different distance shells and identified 324 neighboring open clusters, including 223 reported open clusters and 101 newly discovered open clusters (named as OCSN, Open Cluster of Solar Neighborhood). Our discovery has increased the number of open clusters in the solar neighborhood by about 45\%. In this work, larger spatial extents and more member stars were attained for our cluster sample. We provided the member stars and the membership probabilities through the pyUPMASK algorithm for each cluster and derived their astrophysical, age, and structural parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiaoting Fu
Angela Bragaglia
Chao Liu
Huawei Zhang
Yan Xu
Ke Wang
Zhi-Yu Zhang
Jing Zhong
Jiang Chang
Lu Li
Li Chen
Yang Chen
Fei Wang
Eda Gjergo
Chun Wang
Nannan Yue
Xi Zhang
摘要： Open Clusters are born and evolve along the Milky Way plane, on them is imprinted the history of the Galactic disc, including the chemical and dynamical evolution. Chemical and dynamical properties of open clusters can be derived from photometric, spectroscopic, and astrometric data of their member stars. Based on the photometric and astrometric data from the Gaia mission, the membership of stars in more than 2000 Galactic clusters has been identified in the literature. The chemical and kinematical properties, however, are still poorly known for many of these clusters. In synergy with the large spectroscopic survey LAMOST (data release 8) and Gaia (data release 2), we report a new comprehensive catalogue of 386 open clusters. This catalogue has homogeneous parameter determinations of radial velocity, metallicity, and dynamical properties, such as orbit, eccentricity, angular momenta, total energy, and 3D Galactic velocity. These parameters allow the first radial velocity determination and the first spectroscopic [Fe/H] determination for 44 and 137 clusters, respectively. The metallicity distribution of majority clusters shows falling trends in the parameter space of the Galactocentric radius, the total energy, and the Z component of angular momentum -- except for two old groups that show flat tails in their own parameter planes. Cluster populations of ages younger and older than 500 Myrs distribute diversely on the disc. The latter has a spatial consistency with the Galactic disc flare. The 3-D spatial comparison between very young clusters (< 100 Myr) and nearby molecular clouds revealed a wide range of metallicity distribution along the Radcliffe gas cloud wave, indicating a possible inhomogeneous mixing or fast star formation along the wave. This catalogue would serve the community as a useful tool to trace the chemical and dynamical evolution of the Milky Way.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Wu-Zhen Li
Chen Yang
Zhi-Yuan Zhou
Yan Li
Yin-Hai Li
Su-Jian Niu
Zheng Ge
Li Chen
Guang-Can Guo
Bao-Sen Shi
摘要： The change in the relative phase between two light fields serves as a basic principle for the measurement of the physical quantity that guides this change. It would therefore be highly advantageous if the relative phase could be amplified to enhance the measurement resolution. One well-known method for phase amplification involves the use of the multi-photon number and path entangled state known as the NOON state; however, a high-number NOON state is very difficult to prepare and is highly sensitive to optical losses. Here we propose and experimentally demonstrate in principle a phase amplifier scheme with the assistance of a harmonic generation process. The relative phase difference between two polarization modes in a polarized interferometer is amplified coherently four times with cascaded second-harmonic generation processes. We demonstrate that these amplification processes can be recycled and therefore have the potential to realize much higher numbers of multiple amplification steps. The phase amplification method presented here shows considerable advantages over the method based on NOON states and will be highly promising for use in precision optical measurements.
分类： 生物学 >> 生物化学 提交时间： 2020-02-12
Yingxia Liu
Cong Zhang
Fengming Huang
Yang Yang
Fuxiang Wang
Jing Yuan
Zheng Zhang
Yuhao Qin
Xiaoyun Li
Dandan Zhao
Shunwang Li
Shuguang Tan
Zhaoqin Wang
Jinxiu Li
Chenguang Shen
Jianming Li
Ling Peng
Weibo Wu
Mengli Cao
Li Xing
摘要： 最近，在中国武汉爆发了肺炎病例，由一种名为2019-CoV的新型冠状病毒引起。我们之前的研究中，根据中国深圳的12例2019-nCoV感染患者的临床特征，所有病例均患有肺炎，一半病例发展为急性呼吸窘迫综合征（ARDS）。本文中，我们针对这12例患者的血浆因子表达谱进行了研究。我们测试了2019-nCoV感染患者血浆中的48个因子的表达，其中38个因子与健康个体相比显着升高；2019-nCoV感染的重症患者血浆中的高细胞因子血症水平显著低于A型流感病毒H7N9感染患者，而略高于细菌感染患者。在这38个细胞因子中，有17个与2019-CoV病毒载量相关，其中的15个（M-CSF，IL-10，IFN-α2，IL-17，IL-4，IP-10，IL-7，IL-1受体拮抗剂，G-CSF，IL-12 （p40），IFN-γ，IL-1α，IL-2，HGF和PDGF-BB）与肺损伤Murray评分高度相关，可用来预测2019-nCoV感染患者的疾病严重程度。我们的研究结果表明，这15种高细胞因子可能是衡量2019-nCoV感染患者疾病严重程度的潜在生物标志物，影响这些信号传递介质的因子可能是针对新型2019-nCoV大流行的潜在药物。
分类： 生物学 >> 生物化学 提交时间： 2020-02-08
Yingxia Liu
Yang Yang
Cong Zhang
Fengming Huang
Fuxiang Wang
Jing Yuan
Zhaoqin Wang
Jingxiu Li
Jianming Li
Cheng Feng
Zheng Zhang
Lifei Wang
Ling Peng
Li Chen
Yuhao Qin
Dandan Zhao
Shuguang Tan
Lu Yin
Jun Xu
Congzhao Zhou
摘要： 新型冠状病毒（2019-nCoV）自2019年12月在湖北省武汉市爆发，并迅速传播到中国多地及其他国家。在本研究中，我们报告了来自中国深圳早期的2019-nCoV感染患者的流行病学、临床指标、生化指标和影像学特征，以及可用于预测疾病严重程度的潜在生物标记物。所有12例2019-nCoV感染的肺炎患者均发展为肺炎，其中一半患者进一步发展为急性呼吸窘迫综合征（acute respiratory distress syndrome，ARDS）。最常见的实验室检测生化指标异常是低白蛋白（albumine，ALB）血症、淋巴细胞（lymphocytes，LYM）计数减少，淋巴细胞百分比和中性粒细胞（neutrophils，NEU）百分比降低，C反应蛋白（C-reactive protein，CRP）和乳酸脱氢酶（lactate dehydrogenase，LDH）水平升高，以及CD8细胞计数降低。从患者呼吸道特别是下呼吸道检测到的2019-nCoV病毒滴度与肺部疾病的严重程度正相关。 ALB、LYM、LYM（%）、LDH、NEU（％）和CRP的水平与急性肺损伤程度高度相关。年龄、病毒滴度、肺损伤评分和血液生化指标：ALB、CRP、LDH、LYM（%）、LYM和NEU（%）可能是疾病严重程度的预测指标。此外， 2019-nCoV感染患者的血浆血管紧张素II水平显着升高，并且与病毒滴度和肺损伤程度线性相关。我们的研究结果提供了多种潜在的可用于诊断的生物标志物， 并提出了血管紧张素 II受体阻滞剂（angiotensin II receptor blocker，ARB）药物或可作为治疗2019-nCoV感染的潜在药物进行深入研究。
分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2018-03-30
Jian Zhang
Xiaoying Qin
Di Li
Chunjun Song
Xiaoguang Zhu
Yongfei Liu
Hongxing Xin
Li Chen
Tianhua Zou
摘要： Gd-doped compounds CuGa1-xGdxTe2 (0x0.02) incorporated with tellurium nanoparticles are synthesized by fusion method. Their thermoelectric properties are investigated in the temperature range of 300-800K. The results indicate that the synergistic effect of Gd-doping and Te incorporation remarkably enhances the thermoelectric performance of CuGaTe2. Specially, the thermal conductivity of the specimen CuGa0.98Gd0.02Te2/0.7vol.%Te reduces to 0.45 Wm-1K-1 at 684K, which is ~74% smaller than that of pure CuGaTe2 (=1.76 Wm-1K-1 at 684K) due to the incorporation of nanostructure Te. The thermoelectric figure of merit value (ZT) reaches 0.75 at 737K for the specimen CuGa0.99Gd0.01Te2/0.7vol.%Te, which is ~115% larger than that of pure CuGaTe2.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
TiPei Li
ShaoLin Xiong
ShuangNan Zhang
FangJun Lu
LiMing Song
XueLei Cao
Zhi Chang
Gang Chen
Li Chen
TianXiang Chen
Yong Chen
YiBao Chen
YuPeng Chen
Wei Cui
WeiWei Cui
JingKang Deng
YongWei Dong
YuanYuan Du
MinXue Fu
GuanHua Gao
摘要： Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, osmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard Insight-HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area (~1000 cm2) and microsecond time resolution in 0.2-5 MeV. In addition, Insight-HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the nexpected weak and soft nature of GRB 170817A. Meanwhile, Insight-HXMT/HE provides one of the most stringent constraints (~10-7 to 10-6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.
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