分类： 天文学 >> 天体力学 分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2024-04-20
摘要： 本文简要介绍新的对称形式的质点动力学方程对天体动力学理论的系统性改进。 首先，对于开放的多体系统，无法找到近似程度非常高的惯性系，在传统理论中不得不引入惯性系的近似，而对称新方程因为可以直接适用于任意的平动参考系而避免了惯性系的近似，从而可以提高理论预言的精度。其次，对于束缚的多体系统，传统理论的动力学应用是先引入质心参考系，在质心参考系中应用牛顿第二定律，然后通过坐标变换再转化到实体参考系，比如太阳系的行星摄动方程。 但是，应用对称新方程则可以一步到位推导得到行星摄动方程。最后，如果进一步考虑行星受到临时推力或者冲击力，甚至为了进一步提高计算精度进而考虑来自束缚系统外的作用力，则一个可以叠加非微扰作用力的行星摄动的修正方程在本文得到了确立。
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-18 合作期刊: 《天文技术与仪器（英文）》
摘要：Radioheliographs can obtain solar images at high temporal and spatial resolution, with a high dynamic range. These are among the most important instruments for studying solar radio bursts, understanding solar eruption events, and conducting space weather forecasting. This study aims to explore the effective use of radioheliographs for solar observations, specifically for imaging coronal mass ejections (CME), to track their evolution and provide space weather warnings. We have developed an imaging simulation program based on the principle of aperture synthesis imaging, covering the entire data processing flow from antenna configuration to dirty map generation. For grid processing, we propose an improved non-uniform fast Fourier transform (NUFFT) method to provide superior image quality. Using simulated imaging of radio coronal mass ejections, we provide practical recommendations for the performance of radioheliographs. This study provides important support for the validation and calibration of radioheliograph data processing, and is expected to profoundly enhance our understanding of solar activities.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-18 合作期刊: 《天文技术与仪器（英文）》
摘要：Ancient China recorded a wealth of astronomical observations, notably distinguished by the inclusion of empirical measurements of stellar observations. However, determining the precise observational epochs for these datasets poses a formidable challenge. This study employs the generalized Hough transform methodology to analyze two distinct sets of observational data originating from the Song and Yuan dynasties, allowing accurate estimation of the epochs of these stellar observations. This research introduces a novel and systematic approach, offering a scholarly perspective for the analysis of additional datasets within the domain of ancient astronomical catalogs in future investigations.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-18 合作期刊: 《天文技术与仪器（英文）》
摘要：The high frequency-very high frequency (HF-VHF) frequency band is of significant importance in astronomical observations, with applications studying various phenomena such as space weather, solar radio emissions, planetary eruptions in the solar system, pulsars, transient sources, and reionization of the early universe. This article introduces the HF-VHF frequency band multifunctional radio astronomical terminal system based on a dual-channel high-speed acquisition board with a frequency observation range of 1−250 MHz and a sampling rate of 500 Msps (Mega samples per second). The maximum quantization bit of the system is 14 bits, with a maximum time resolution of 0.1 s and a maximum spectral resolution of 16 kHz. The system combines spectral analysis of solar radio signals and recording of time-domain data of signals interfering with long baselines, and adopts a server-client separation mode to allow remote operation with separate permissions. It is used in the China-Malaysia joint astronomy project, which can carry out single-site observation of solar radio signals as well as interferometric observation of signals from multiple sites.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-18 合作期刊: 《天文技术与仪器（英文）》
摘要：Optical frequency combs, as powerful tools for precision spectroscopy and research into optical frequency standards, have driven continuous progress and significant breakthroughs in applications such as time-frequency transfer, measurement of fundamental physical constants, and high-precision ranging, achieving a series of milestone results in ground-based environments. With the continuous maturation and evolution of femtosecond lasers and related technologies, optical frequency combs are moving from ground-based applications to astronomical and space-based applications, playing an increasingly important role in atomic clocks, exoplanet observations, gravitational wave measurements, and other areas. This paper, focusing on astronomical and space-based applications, reviews research progress on astronomical frequency combs, optical clock time-frequency networks, gravitational waves, dark matter measurement, dual-comb large-scale absolute ranging, and high-resolution atmospheric spectroscopy. With enhanced performance and their gradual application in the field of space-based research, optical frequency combs will undoubtedly provide more powerful support for astronomical science and cosmic exploration in the future.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-18 合作期刊: 《天文技术与仪器（英文）》
Lanqiang Zhang
Xuejun Rao
Hua Bao
Youming Guo
Jinsheng Yang
Nanfei Yan
Xian Ran
Dingkang Tong
Xinlong Fan
Zhongyi Feng
Changhui Rao
摘要：Adaptive optics (AO) is essential for high-quality ground-based observations with large telescopes because it counters the impact of wavefront aberrations caused by atmospheric turbulence. The new vacuum solar telescope（NVST） is one of the most important high-resolution solar observation instruments in the world. Three sets of solar adaptive optics systems have been developed and installed on this telescope: conventional adaptive optics, ground layer adaptive optics, and multi- conjugate adaptive optics. These have been in operation from 2018 to 2023. This paper details the development and application of solar adaptive optics on the NVST and discusses the newest instrumentation.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-18 合作期刊: 《天文技术与仪器（英文）》
摘要：Strong atmospheric turbulence reduces astronomical seeing, causing speckle images acquired by groundbased solar telescopes to become blurred and distorted. Severe distortion in speckle images impedes image phase deviation in the speckle masking reconstruction method, leading to the appearance of spurious imaging artifacts. Relying only on linear image degradation principles to reconstruct solar images is insufficient. To solve this problem, we propose the multiframe blind deconvolution combined with non-rigid alignment (MFBD-CNRA) method for solar image reconstruction. We consider image distortion caused by atmospheric turbulence and use non-rigid alignment to correct pixel-level distortion, thereby achieving nonlinear constraints to complement image intensity changes. After creating the corrected speckle image, we use the linear method to solve the wavefront phase, obtaining the target image. We verify the effectiveness of our method results, compared with others, using solar observation data from the 1 m new vacuum solar telescope (NVST). This new method successfully reconstructs high-resolution images of solar observations with a Fried parameter r0 of approximately 10 cm, and enhances images at high frequency. When r0 is approximately 5 cm, the new method is even more effective. It reconstructs the edges of solar graining and sunspots, and is greatly enhanced at mid and high frequency compared with other methods. Comparisons confirm the effectiveness of this method, with respect to both nonlinear and linear constraints in solar image reconstruction. This provides a suitable solution for image reconstruction in ground-based solar observations under strong atmospheric turbulence.
分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-16 合作期刊: 《天文技术与仪器（英文）》
Peng Jiang
Rurong Chen
Hengqian Gan
Jinghai Sun
Boqin Zhu
Hui Li
Weiwei Zhu
Jingwen Wu
Xuelei Chen
Haiyan Zhang
Tao An
摘要：The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) Core Array is a proposed extension of FAST, integrating 24 secondary 40-m antennas implanted within 5 km of the FAST site. This original array design will combine the unprecedented sensitivity of FAST with a high angular resolution (4.3" at a frequency of 1.4 GHz), thereby exceeding the capabilities at similar frequencies of next-generation arrays such as the Square Kilometre Array Phase 1 or the next-generation Very Large Array. This article presents the technical specifications of the FAST Core Array, evaluates its potential relatively to existing radio telescope arrays, and describes its expected scientific prospects. The proposed array will be equipped with technologically advanced backend devices, such as real-time signal processing systems. A phased array feed receiver will be mounted on FAST to improve the survey efficiency of the FAST Core Array, whose broad frequency coverage and large field of view（ FOV） will be essential to study transient cosmic phenomena such as fast radio bursts and gravitational wave events, to conduct surveys and resolve structures in neutral hydrogen galaxies, to monitor or detect pulsars, and to investigate exoplanetary systems. Finally, the FAST Core Array can strengthen China's major role in the global radio astronomy community, owing to a wide range of potential scientific applications from cosmology to exoplanet science.
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 类星体有剧烈、大幅度的光变现象, 光变研究有助于建立与观测相符的理论模型. 这篇文章从密歇根大学射电天文台数据库收集了类星体3C 446射电4.8、8.0和14.5\;GHz波段的长期观测数据. 传统的线性方法难以分析复杂的光变现象, 文章采用了集合经验模态分解(Ensemble Empirical Mode Decomposition, EEMD)方法和非线性分析方法相结合, 从混沌动力学特性、分形特性和周期性多角度对类星体光变随时间演化的规律进行了较全面的分析, 并重点对比分析了除去周期成分或混沌成分前后, 光变的周期性和非线性特性是否存在明显区别. 分析结果表明, 类星体3C 446射电波段光变资料由周期成分、趋势成分和混沌成分组成, 光变具有周期性、混沌性和分形特性. 除去混沌成分和趋势成分后的光变周期与原始光变资料的周期完全相同, 而两者的混沌和分形特性有明显不同. 从饱和关联维数来看, 重构动力学系统时, 除去周期成分和趋势成分后的光变资料比原始光变资料需要更多的独立参量, Kolmogorov熵值表明前者信息的损失率比后者大, 系统的混沌程度更高, 系统也更复杂, Hurst值表明后者自相似性和长程相关性比前者略强.
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 年轻脉冲星多处于超新星遗迹(Supernova Remnant, SNR)中, 其分为转动供能脉冲星(Rotation-powered SNR-PSR)、磁星(Magnetar)和中心致密天体(Central Compact Object, CCO), 这3类年轻脉冲星有着不同的自旋周期及磁场强度分布. 其中, 遗迹磁星(SNR-Magnetar)的平均自旋周期比转动供能遗迹脉冲星大近一个量级, 平均磁场强度高近两个量级. 同时, 中心致密天体比转动供能遗迹脉冲星的平均磁场强度低近两个量级. 这3类年轻脉冲星不同的物理性质, 可能源于其不同的前身星或不同的超新星爆发过程, 也可能源于其中子星诞生后的不同演化过程. 此外, 转动供能遗迹脉冲星比年轻的转动供能非遗迹脉冲星具有更快的平均自旋周期、更大的平均磁场强度和更短的平均特征年龄. 这暗示新诞生的中子星经时间约为105--106\;yr的演化过程, 其自旋速度将减小近一半, 同时其磁场强度也将衰减近一半.
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 利用中国科学院新疆天文台南山观测站26\;m射电望远镜, 在中心频率1556\;MHz, 对Crab脉冲星(PSR B0531+21)进行了长达12.6\;h的连续观测, 观测带宽为512\;MHz, 时间分辨率为32\;\upmus, 研究了巨脉冲辐射的等待时间分布特征. 观测共探测到2097个信噪比大于10的巨脉冲, 对应的流量密度大于100\;Jy. 巨脉冲的爆发率表现为高度的间歇性, 在较短的时间内具有较高的爆发率, 在相对长的宁静期内巨脉冲的爆发率较低, 尤其是中间脉冲相位内的巨脉冲爆发. 相邻两个巨脉冲的等待时间分布表现为幂律分布特征, 可以用一个非稳态的泊松过程进行模拟, 这表明巨脉冲的爆发是一种独立的随机事件. 此外, 主脉冲和中间脉冲相位上的巨脉冲具有不同的等待时间分布特征, 这意味着脉冲星不同磁极的巨脉冲辐射机制可能是不同的. 这些观测结果对于理解脉冲星的射电辐射机制具有重要意义.
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 低表面亮度星系(Low Surface Brightness Galaxy, LSBG)的特征对于理解星系整体特征非常重要, 通过现代的机器学习特别是深度学习算法来搜寻扩充低表面亮度星系样本具有重要意义. LSBG因特征不明显而难以用传统方法进行自动和准确辨别, 但深度学习确具有自动找出复杂且有效特征的优势, 针对此问题提出了一种可用于在大样本巡天观测项目中搜寻LSBG的算法---YOLOX-CS (You Only Look Once YOLOX-CS在扩充前后两个数据集中搜索LSBG的召回率和AP (Average Precision)值都有较好的测试结果, 其在未扩充数据集的测试集中的召回率达到97.75\%, AP值达到97.84\%, 在DCGAN模型扩充的数据集中, 同样测试集下进行实验的召回率达到99.10\%, AP值达到98.94\%, 验证了该算法在LSBG搜索中具有优秀的性能. 最后, 将该算法应用到SDSS部分测光数据上, 搜寻得到了765个LSBG候选体.version X-CS). 首先通过实验对比5种经典目标检测算法并选择较优的YOLOX算法作为基础算法, 然后结合不同注意力机制和不同优化器, 构建了YOLOX-CS的框架结构. 数据集使用的是斯隆数字化巡天(Sloan Digital Sky Survey, SDSS)中的图像, 其标签来自于\alpha.40-SDSS DR7 (40\%中性氢苜蓿巡天与第7次数据发布的斯隆数字化巡天的交叉覆盖天区)巡天项目中的LSBG, 由于该数据集样本较少, 还采用了深度卷积生成对抗网络(Deep Convolutional Generative Adversarial Networks, DCGAN)模型扩充了实验测试数据. 通过与一系列目标检测算法对比后,
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 星系的形态与星系的形成和演化息息相关, 其形态学分类是星系天文学后续研究的重要一环. 当前海量天文观测数据的出现使得天文数据自动分析方法越来越得到重视, 针对此问题, 利用先进的深度学习骨干网络EfficientNetV2, 分析不同的注意力机制类型和使用节点对网络性能的影响, 构建了一种命名为EfficientNetV2-S-Triplet7 (即在EfficientNetV2-S stage7的1\times1卷积层后加入Triplet模块)的改进算法模型来实现星系形态学的自动分类. 使用第二期星系动物园(Galaxy Zoo 2, GZ2)中超过24万张的测光图像作为初始数据进行实验测试. 在对数据进行预处理时采取了尺寸抖动、翻转、色彩畸变等图像增强手段来解决图像数量的不平衡问题. 在同一系列经典和前沿的深度学习算法模型AlexNet、ResNet-34、MobileNetV2、RegNet进行对比实验后, 得出EfficientNetV2-S-Triplet7算法在分类准确率、查全率和F1分数等指标上具有最好的测试结果. 在9375张测试图像中的3项指标值分别可达到89.03\%、90.21\%、89.93\%, 查准率达到89.69\%, 在其他模型中排在第3位. 该结果表明将EfficientNetV2-S-Triplet7算法应用于大规模星系数据的形态学分类任务中有很好的效果.
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 随着天文探测技术的快速发展, 海量的星系图像数据不断产生, 能够及时高效地对星系图像进行形态分类对研究星系的形成与演化至关重要. 针对传统的星系形态分类模型特征选择困难、分类速度慢、准确率受限等难题, 提出一种以Inception-v3神经网络为主干结构, 融合压缩激励(Squeeze and Excitation Network, SE)通道注意力机制的星系形态分类模型. 该模型在斯隆数字巡天(Sloan Digital Sky Survey, SDSS)样本的测试集准确率高达99.37\%. 旋涡星系、圆形星系、中间星系、雪茄状星系与侧向星系的F1值分别为99.33\%、99.58\%、99.33\%、99.41\%与99.16\%. 该模型与Inception-v3、MobileNet (Mobile Neural Network)和ResNet (Residual Neural Network)网络模型相比, SE-Inception-v3宽度和深度优势表现出更强的特征提取能力, 可以高效识别不同形态的星系, 为未来大型巡天计划的大规模星系形态分类问题提供了一种新方法.
分类： 天文学 提交时间： 2024-04-12 合作期刊: 《天文学报》
摘要： 地基光学天文望远镜是人类探索与研究宇宙的重要手段, 对已有地基光学台址的光学观测环境进行监测分析, 可以为后期设备针对性改造以及观测者调整观测策略提供参考依据, 对提升地基光学设备的观测效能具有重要的意义. 吉林天文观测基地(简称``基地'')隶属于中国科学院国家天文台长春人造卫星观测站, 位于吉林省吉林市大绥河镇小绥河村南沟约5 km处(东经126.3{\circ}, 北纬43.8{\circ}, 海拔高度313\;m). 基地大气视宁度均值范围约为1.3''--1.4''、天顶附近V波段的天光背景亮度为20.64\;mag\,\cdot\,arcsec {-2}、年晴夜数最高可达270余天, 具有良好的天文观测条件. 吉林天文观测基地于2016年投入运行, 现有1.2\;m光电望远镜、迷你光电阵列望远镜、大视场光电望远镜阵列、新型多功能阵列结构光电探测平台等多台(套)光电望远镜设备. 利用上述设备, 主要围绕空间目标探测与识别、精密轨道确定、光电探测新方法以及变源天体的多色测光等开展相关研究工作, 与多家国内高校及科研院所保持着良好的合作关系.
分类： 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类： 天文学 >> 天文学 提交时间： 2024-04-11
摘要： The electromagnetic fields of point sources with time varying charges moving in the vacuum are derived using the Liénard-Wiechert potentials. The properties of the propagation velocities and the Doppler effect are discussed based on their far fields. The results show that the velocity of the electromagnetic waves and the velocity of the sources cannot be added like vectors; the velocity of electromagnetic waves of moving sources are anisotropic in the vacuum; the transverse Doppler shift is intrinsically included in the fields of the moving sources and is not a pure relativity effect caused by time dilation. Since the fields are rigorous solutions of the Maxwell’s equations, the findings can help us to abort the long-standing misinterpretations concerning about the classic mechanics and the classic electromagnetic theory. Although it may violate the theory of the special relativity, we show mathematically that, when the sources move faster than the light in the vacuum, the electromagnetic barriers and the electromagnetic shock waves can be clearly predicted using the exact solutions. Since they cannot be detected by observers in the region outside their shock wave zones, an intuitive and reasonable hypothesis can be made that the superluminal sources may be considered as a kind of electromagnetic blackholes.
分类： 天文学 >> 天文学史 分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-10
摘要： 中国古代保留着丰富的天文观测记录，其中尤为宝贵的是大量实测的恒星观测数据。然而，确定这些观测数据的年代是一个相当复杂的问题。本文以宋元时代的两组观测数据为基础，运用广义霍夫变换的技术手段对数据进行计算和分析。我们成功地获得了对恒星观测年代的较为准确的估算结果。这一方法为未来分析更多古代天文星表数据提供了新的途径和视角。
分类： 天文学 >> 天文学史 分类： 天文学 >> 天文仪器与技术 提交时间： 2024-04-10
摘要： 中国古代保留着丰富的天文观测记录，其中尤为宝贵的是大量实测的恒星观测数据。然而，确定这些观测数据的年代是一个相当复杂的问题。本文以宋元时代的两组观测数据为基础，运用广义霍夫变换的技术手段对数据进行计算和分析。我们成功地获得了对恒星观测年代的较为准确的估算结果。这一方法为未来分析更多古代天文星表数据提供了新的途径和视角。
分类： 天文学 >> 天文学 提交时间： 2024-03-30
Niankun Yu
Zheng Zheng
Chao-Wei Tsai
Pei Zuo
Sara L. Ellison
David V. Stark
Di Li
Jingwen Wu
Karen L. Masters
Ting Xiao
Yinghui Zheng
Zongnan Li
Kai Zhang
Hongying Chen
Shu Liu
Sihan Jiao
Fanyi Meng
摘要： The atomic-to-molecular gas conversion is a critical step in the baryon cycle of galaxies, which sets the initial conditions for subsequent star formation and influences the multi-phase interstellar medium. We compiled a sample of 94 nearby galaxies with observations of multi-phase gas contents by utilizing public H I, CO, and optical IFU data from the MaNGA survey together with new FAST H I observations. In agreement with previous results, our sample shows that the global molecular-to-atomic gas ratio ($R_{\rm mol} \equiv$ log $M_{\rm H_2}/M_{\rm H\ I}$) is correlated with the global stellar mass surface density $\mu_*$ with a Kendall's $\tau$ coefficient of 0.25 and $p < 10^{-3}$, less tightly but still correlated with stellar mass and NUV$-$ r color, and not related to the specific star formation rate (sSFR). The cold gas distribution and kinematics inferred from the H I and CO global profile asymmetry and shape do not significantly rely on $R_{\rm mol}$. Thanks to the availability of kpc-scale observations of MaNGA, we decompose galaxies into H II, composite, and AGN-dominated regions by using the BPT diagrams. With increasing $R_{\rm mol}$, the fraction of H II regions within 1.5 effective radius decreases slightly; the density distribution in the spatially resolved BPT diagram also changes significantly, suggesting changes in metallicity and ionization states. Galaxies with high $R_{\rm mol}$ tend to have high oxygen abundance, both at one effective radius with a Kendall's $\tau$ coefficient of 0.37 ($p < 10^{-3}$) and their central regions. Among all parameters investigated here, the oxygen abundance at one effective radius has the strongest relation with global $R_{\rm mol}$, but the dependence of gas conversion on gas distribution and galaxy ionization states is weak.
分类： 天文学 >> 天文学 提交时间： 2024-03-29
摘要： 针对长期有争议的万有引力问题,论述了空间物体从小、大至星体的发展是以物体的转动惯量(I)为特征的自然进化过程.用时间、路径、质量三个因素说明I这一特征:时间说明I物体从小至今的持续时长;路径说明I是一种自然匀速行进的惯性物体,但在行进中其惯性作用在空间产生了以空间介质为媒介的惯介力矩,该力矩通过空间介质与另一物体产生关联逐渐形成了椭圆轨道;质量说明了质量的变化情况,在I与其他物体关联后会渐渐地归并另外物体,使其质量增加，则I相应增强. 给出了两个在空间相关星体的惯量平衡方程,由方程解出两物体的空间平衡点,通过地球、月球系统的真实数据和平衡点数据获得双方对应的运行轨迹、用以测定两者的紧密程度的刚性惯力与惯介力的比值、和两个星体的加速度原理及各自加速度计算值,经比对证明惯动平衡方程的正确性.这一成果对进一步理解太阳系的惯性特征将会有很大的促进作用.
点击量
待评议
点击量
下载量
评论
通过
