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 >> 天体物理学 分类： 天文学 >> 恒星和银河系 提交时间： 2018-09-12
Dai, zhibin
Szkody, Paula
Kennedy, Mark
Su Jie
Medagangoda, N. Indika
Robinson, Edward L.
Garnavich, Peter M.
De Silva, L. Malith M.
摘要： We used the light curve code XRBinary to model the quiescent K2 light curves of three low-inclination cataclysmic variables (CVs): 1RXS\,J0632+2536 (J0632+2536), RZ\,Leo, TW\,Vir and the pre-CV WD\,1144+011. Optimized light curve models were obtained using a nonlinear fitting code NMfit and visualized by Phoebe 2.0. The disk model of J0632+2536 shows that one hotspot at the edge of the disk is enough to describe its light curve, while the other two dwarf nova (DN): RZ\,Leo and TW\,Vir require two hotspots. A typical pre-CV model with a weak irradiation effect for WD\,1144+011 can explain its single-hump modulation and the newly observed spectrum confirms its previous classification. The synthetic analyses for the DN clearly indicate that phase zero of the double-hump modulations occurs around the secondary minimum and the primary hump is mainly caused by the hotspot at the edge of the disk. The quiescent disk has a flat temperature distribution with a power index of $\sim0.11$. The disk model of RZ\,Leo implies a truncated disk, supporting its previously speculated classification as an intermediate polar (IP). Except for the IP model of RZ\,Leo, which lacks a component related to the inferred accretion curtain, the models of J0632+2536, TW\,Vir and WD\,1144+011 are consistent with results from the Gaia mission. The derived masses and radii of the secondaries of the three DN are consistent with the semi-empirical relations for CV donor stars, while their effective temperatures are higher than the predictions. Irradiation of the donor stars is investigated to explain this discrepancy.
分类： 天文学 >> 天体测量学 分类： 图书馆学、情报学 >> 情报学 分类： 物理学 >> 原子与分子物理学 提交时间： 2021-03-05
摘要： 2015年激光干涉仪引力波天文台（Laser Interferometer Gravitational-wave Observatory，LIGO）直接检测到引力波信号，为新物理学和天体物理学带来希望的同时，也掀起激光干涉仪引力波探测器发展的新浪潮。在激光干涉仪引力波探测器从地面到太空蓬勃发展的大背景下，本文从建设历程、技术特色和发展定位、运营模式等方面，开展各探测器的对比研究，归纳出激光干涉仪引力波探测器建设和运营的经验启示，即：激光干涉仪引力波探测器的建设是长期化工程，有助于推动科研容错机制和科学评价机制的完善发展；激光干涉仪引力波探测器的建设是高科技工程，有助于推动多学科技术协同发展；激光干涉仪引力波探测器的建设是国际化工程，有助于推动科研合作健康发展。
分类： 天文学 >> 天体物理学 分类： 天文学 >> 天文学 提交时间： 2023-08-31
摘要： The radiation mechanism of fast radio bursts (FRBs) has been extensively studied but still remains elusive. Coherent radiation is identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and the magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.
分类： 天文学 >> 恒星和银河系 提交时间： 2023-12-31
Hong-Liang Yan
Jian-Rong Shi
Yu-Tao Zhou
Yong-Shou Chen
Er-Tao Li
Suyalatu Zhang
Shao-Lan Bi
Ya-Qian Wu
Zhi-Hong Li
Bing Guo
Wei-Ping Liu
Qi Gao
Jun-Bo Zhang
Ze-Ming Zhou
Hai-Ning Li
Gang Zhao
摘要： About 1% of giants have anomalously high Li abundances in their atmospheres, conflicting directly with the prediction of the standard stellar evolution models. This finding makes the production and evolution of Li in the Universe intriguing, not only in the sense of Big Bang nucleosynthesis or the interstellar medium, but also for the evolution of stars. Decades of efforts have been put into explaining why such extreme objects exist, yet the origins of Lirich giants are still being debated. Here we report the discovery of the most Li-rich giant known to date, with a very high Li abundance of 4.51. This rare phenomenon was observed coincidentally with another short-term event: the star is experiencing its luminosity bump on the red giant branch. Such a high Li abundance indicates that the star might be at the very beginning of its Li-rich phase, which provides a great opportunity to investigate the origin and evolution of Li in the Galaxy. A detailed nuclear simulation is presented with up-to-date reaction rates to recreate the Li enrichment process in this star. Our results provide tight constraints on both observational and theoretical points of view, suggesting that low-mass giants can internally produce Li to a very high level through 7Be transportation during the red giant phase.
分类： 天文学 >> 恒星和银河系 提交时间： 2023-10-09
摘要： Symbiotic stars are interacting binary systems, making them valuable for studying various astronomical phenomena, such as stellar evolution, mass transfer, and accretion processes. Despite recent progress in the discovery of symbiotic stars, a significant discrepancy between the observed population of symbiotic stars and the number predicted by theoretical models. To bridge this gap, this study utilized machine learning techniques to efficiently identify new symbiotic stars candidates. Three algorithms (XGBoost, LightGBM, and Decision Tree) were applied to a dataset of 198 confirmed symbiotic stars and the resulting model was then used to analyze data from the LAMOST survey, leading to the identification of 11,709 potential symbiotic stars candidates. Out of the these potential symbiotic stars candidates listed in the catalog, 15 have spectra available in the SDSS survey. Among these 15 candidates, two candidates, namely V* V603 Ori and V* GN Tau, have been confirmed as symbiotic stars. The remaining 11 candidates have been classified as accreting-only symbiotic star candidates. The other two candidates, one of which has been identified as a galaxy by both SDSS and LAMOST surveys, and the other identified as a quasar by SDSS survey and as a galaxy by LAMOST survey.
分类： 天文学 >> 恒星和银河系 提交时间： 2022-04-20
摘要： We report the discovery of a massive protostar M17~MIR embedded in a hot molecular core in M17. The multiwavelength data obtained during 1993--2019 show significant mid-IR (MIR) variations, which can be split into three stages: the decreasing phase during 1993.03--mid-2004, the quiescent phase from mid-2004 to mid-2010, and the rebrightening phase from mid-2010 until now. The variation of the 22\,GHz H2O maser emission, together with the MIR variation, indicates an enhanced disk accretion rate onto M17~MIR during the decreasing and rebrightening phases. Radiative transfer modeling of the spectral energy distributions of M17~MIR in the 2005 epoch (quiescent) and 2017 epoch (accretion outburst) constrains the basic stellar parameters of M17~MIR, which is an intermediate-mass protostar (M~5.4 Msun) with accretion rate ~1.1x10^-5 Msun in the 2005 epoch and ~1.7x10^-3 Msun/yr in the 2017 epoch. The enhanced accretion rate during outburst induces the luminosity outburst L7600Lsun. In the accretion outburst, a larger stellar radius is required to produce accretion rate consistent with the value estimated from the kinematics of water masers. M17 MIR shows two accretion outbursts (t920 yr) with outburst magnitudes of 2 mag, separated by a 6 yr quiescent phase. The accretion outbusrt occupies 83\% of the time over 26 yr. The accretion rate in outburst is variable with amplitude much lower than the contrast between quiescent and outburst phases. The extreme youth of M17 MIR suggests that minor accretion bursts are frequent in the earliest stages of massive star formation.
分类： 天文学 >> 恒星和银河系 提交时间： 2017-08-17
摘要： Aims. The quiescent periodic photometric modulations of two low-inclination cataclysmic variables observed in Kepler K2 Campaigns 0 and 1, KZ Gem and TW Vir, are investigated. Methods. A phase-correcting method was successfully used to detect the orbital modulations of KZ Gem and TW Vir and improve their orbital periods. The light curve morphologies of both CVs were further analyzed by defining flux ratios and creating colormaps. Results. KZ Gem shows ellipsoidal modulations with an orbital period of 0.22242(1) day, twice the period listed in the updated RK catalogue (Edition 7.24). With this newly determined period, KZ Gem is no longer a CV in the period gap, but a long-period CV. A part of the quiescent light curve of TW Vir that had the highest stability was used to deduce its improved orbital period of 0.182682(3) day. The flat patterns shown in the colormaps of the flux ratios for KZ Gem demonstrate the stability of their orbital modulations, while TW Vir show variable orbital modulations during the K2 datasets. In TW Vir, the single versus double-peaked nature of the quiescent orbital variations before and after superoutburst may be related to the effect of the superoutburst on the accretion disk.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-12-08
摘要： This paper presents a morphological investigation of the early-type spiral galaxy M81 (NGC 3031) through decomposition by fitting radial profiles of surface brightness using the software GALFIT, aimed at exploring structural components of M81 and quantifying their morphology. In this work, we adopt 6 types of decompositions with different numbers of morphological components, among which the most complicated one contains 5 components such as a bulge, a disk, a pair of outer spiral arms, a pair of inner spiral arms, and a galactic nucleus. The results show that, M81 hosts a classical bulge with the Sersic index 5.0; the morphology and the luminosity for the bulge are almost constant in the different decomposition types. The disk of M81 has the Sersic index 1.2 but the morphology and the luminosity are found sensitive to the inclusion of the inner spiral arms in the decomposition or not. The results of this work indicate that the combination of individual substructures has a considerable impact on the morphology of the galaxy as a mixture. On the basis of the results, the usability of the different types of decomposition is suggested in this work. The three-component decomposition, i.e., bulge + disk + nucleus, is applicable to statistics of large samples of galaxies; more complicated decomposition with spiral arms taken into account is suitable for precise measurements of individual galaxies in small samples. This work is based on the single-band Spitzer-The Infrared Array Camera (IRAC) 4.5 m image. In the future, we will carry out multi-wavelength decomposition, for the purpose of investigating spectral energy distributions and stellar population properties for the galactic substructures, and thereby deduce their formation history and evolution processes.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-05-24
摘要： We analyse H(z) parameter data with some conditions by using Lagrange mean value theorem in Calculus. We find that: (1) there exists at least one decelerated phase at 1 $ sigma$ confidence level in the redshift range (0.38, 0.59); (2) the equation of motion of dark energy may be less than -1 at 1 confidence level at some redshifts in the redshift range (1.3, 1.53); (3) there exists at least one accelerated phase at 1 confidence level in the redshift range (1.037, 1.944). These results may provide possible evidences for physics beyond $ Lambd ACDM.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Qiuhan He
Ran Li
Carlos S. Frenk
James Nightingale
Shaun Cole
Nicola C. Amorisco
Richard Massey
Andrew Robertson
Amy Etherington
Aristeidis Amvrosiadis
Xiaoyue Cao
摘要： We rederive the number density of intervening line-of-sight haloes relative to lens subhaloes in galaxy-galaxy strong lensing observations, where these perturbers can generate detectable image fluctuations. Previous studies have calculated the detection limit of a line-of-sight small-mass dark halo by comparing the lensing deflection angles it would cause, to those caused by a subhalo within the lens. However, this overly simplifies the difference in observational consequences between a subhalo and a line-of-sight halo. Furthermore, it does not take into account degeneracies between an extra subhalo and the uncertain properties of the main lens. More in keeping with analyses of real-world observations, we regard a line-of-sight halo as detectable only if adding it to a smooth model generates a statistically significant improvement in the reconstructed image. We find that the number density of detectable line-of-sight perturbers has been overestimated by as much as a factor of two in the previous literature. For typical lensing geometries and configurations, very deep imaging is sensitive to twice as many line-of-sight perturbers as subhaloes, but moderate depth imaging is sensitive to only slightly more line-of-sight perturbers than subhaloes.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
摘要： In this paper we consider the effects of adding curvature in extended cosmologies involving a free-to-vary neutrino sector and different parametrizations of Dark Energy (DE). We make use of the Planck 2018 cosmic microwave background temperature and polarization data, Baryon Acoustic Oscillations and Pantheon type Ia Supernovae data. Our main result is that a non-flat Universe cannot be discarded in light of the current astronomical data, because we find an indication for a closed Universe in most of the DE cosmologies explored in this work. On the other hand, forcing the Universe to be flat can significantly bias the constraints on the equation of state of the DE component and its dynamical nature.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
摘要： Interstellar (ISM) and circumgalactic medium (CGM) around galaxies are linked to several physical processes that drive galaxy evolution. For example, the X-ray emission from the CGM gas around ellipticals has been linked to the AGN feedback occurring in the host. Upcoming telescopes such as HUBS, with ~ 1 eV resolution, can provide us with deep insights about the hot gas properties of such galaxies thus constrain these processes. In this project, we discuss X-ray emission of the ISM and CGM of elliptical galaxies simulated using MACER code. We generate X-ray emission data from the MACER simulations with various feedback models and produce mock observations for an instrument with high spectral resolution, which is a necessary step of selecting sources for the future observations with planned mission such as HUBS. More importantly, we establish connections between the physics of AGN and stellar feedback with the emission spectra from the ISM and CGM to investigate the possibility of using observations to constrain feedback models. We fit the X-ray spectra from these simulations with standard fitting procedures and compare the retrieved physical properties with their counterparts from the simulations to understand whether the future high-resolution observations can reliably reveal the properties of the gas in the galaxies.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Y. T. Yan
C. Henkel
K. M. Menten
Y. Gong
H. Nguyen
J. Ott
A. Ginsburg
T. L. Wilson
A. Brunthaler
A. Belloche
J. S. Zhang
N. Budaiev
D.Jeff
摘要： We report the discovery of widespread maser emission in non-metastable inversion transitions of NH_3 toward various parts of the Sagittarius B2 molecular cloud/star forming region complex: We detect masers in the J,K= (6,3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH_3 (6,3) maser in Sgr B2(NS), and NH_3 (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in A-configuration we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are >3000~K and reach up to several 10^5~K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or UCH{\scriptsize II} regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH{\scriptsize II} regions. Overall, Sgr B2 is unique in that it allows us to measure many NH_3 masers simultaneously, which may be essential to elucidate their so far poorly understood origin and excitation.
分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21
Guang Yang
W. N. Brandt
David M. Alexander
Médéric Boquien
Qingling Ni
Casey Papovich
Justin S. Spilker
Fabio Vito
Jonelle L. Walsh
Chengpeng Zhang
摘要： Recent studies have revealed a strong relation between sample-averaged black-hole (BH) accretion rate (BHAR) and star formation rate (SFR) among bulge-dominated galaxies, i.e., lockstep BH-bulge growth, in the distant universe. This relation might be closely related to the BH-bulge mass correlation observed in the local universe. To understand further BH-bulge coevolution, we present ALMA CO(2-1) or CO(3-2) observations of 7 star-forming bulge-dominated galaxies at z=0.5-2.5. Using the ALMA data, we detect significant (>3) CO emission from 4 objects. For our sample of 7 galaxies, we measure (or constrain with upper limits) their CO line fluxes and estimate molecular gas masses (M_{gas}). We also estimate their stellar masses (M_{star}) and SFRs by modelling their spectral energy distributions (SEDs). Using these physical properties, we derive the gas-depletion timescales (t_{dep} = M_{gas}/SFR) and compare them with the bulge/BH growth timescales (t_{grow} = M_{star}/SFR \sim M_{BH}/BHAR). Our sample generally has t_{dep} shorter than t_{grow} by a median factor of ≳4, indicating that the cold gas will be depleted before significant bulge/BH growth takes place. This result suggests that the BH-bulge lockstep growth is mainly responsible for maintaining their mass relation, not creating it. We note that our sample is small and limited to z<2.5; JWST and ALMA will be able to probe to higher redshifts in the near future.
分类： 物理学 >> 地球物理学、天文学和天体物理学 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 >> 星系和宇宙学 提交时间： 2022-11-03
摘要： 本文以物理学中标准钟和标准尺的定义实质和爱因斯坦的相对论物理为基础，从自然哲学层次出发讨论了物理的时空观。提出在已有的时空标度的概念基础上，应该进一步明确区分时空标度和时空背景。根据爱因斯坦相对论的实际逻辑可以作如下理解，满足相对论性变化的是时空标度，而时空标度是人为地根据物质实体中发生或存在的固有物理事件定义的，时空背景作为反映时空标度的长短或大小变化的必备基础和参考背景，应该是绝对的。空间标度的长短尺度在本质上应该理解为固有物理事件在空间的绝对背景上截取的线段的长度。最后以此时空观为基础，探讨了经典力学框架下的质点动力学方程，自然地得出了新形式的质点动力学方程。新动力学方程可以直接应用到任何实际的，（相对宇宙绝对背景）无转动的参考系中。而惯性力的本质正是作用到参考物体上的真实受力。这一经典质点动力学改造的本质是修正了牛顿第二定律传统体系中存在的一个理论缺陷。然而，可能更为重要的是，在形式上具备明显优越性的新质点动力学方程反过来强烈地暗示了时空背景的绝对性。文章最后结合广义相对论的引力几何化思想，探讨了引力对时空标度的物理效应。
分类： 物理学 >> 地球物理学、天文学和天体物理学 分类： 天文学 >> 星系和宇宙学 提交时间： 2020-09-09
摘要： Motivated by recent work on rotating black hole shadow [Phys. Rev. D101, 084029 (2020)], we investigate the shadow behaviors of rotating Hayward-de Sitter black hole for static observers at a finite distance in terms of astronomical observables. This paper uses the newly introduced distortion parameter in [arXiv:2006.00685] to describe the shadow's shape quantitatively. We show that the spin parameter would distort shadows and the magnetic monopole charge would increase the degree of deformation. At the same time, the distortion could be relieved because of the cosmological constant and the distortion would increase with the distance from the black hole. Besides, the spin parameter, magnetic monopole charge and cosmological constant increase will cause the shadow to shrink.
分类： 天文学 >> 星系和宇宙学 提交时间： 2018-04-25
摘要： 本文是[1]对冲突簇的延续和推广。我们研究冲突子群中的总、暗物质密度分布和关联。就像我们对纽曼星系团所做的那样。就像Newman星系团一样，我们发现密度分布受重子相互作用和能量的影响很大。角动量通过动态摩擦从重子转移到DM。大星系团的暗物质密度剖面的内斜率通常比纳瓦罗-弗伦克-白剖面内坡，最大值为-0.79，最小值为-0.30.如在Newman星系团的情况下，斜率α之间存在一系列的相关性。暗物质剖面，以及：A.团簇的核心半径；B.有效半径Re；C.最明亮的中央星系(BCG)的质量；D.总重子质量和恒星质量星系团。我们还发现了有效半径与病毒质量之间的关系。簇的结构，它们的总密度和密度分布，以及它们之间的相关性是：在两个阶段的情况下理解。在第一个耗散阶段，BGC形成。在第二耗散相，重子团与DM的相互作用动力摩擦(DF)使DM分布趋于平缓。这两个阶段的最终结果是不同DM分布、内部斜率及几种关联的簇的形成簇的特征量
分类： 天文学 >> 星系和宇宙学 提交时间： 2018-03-27
摘要： 在本文中，我们将展示重子物理是如何解决矮星中惊人的多样性问题的。 星系旋转曲线形状。为此，我们比较了SPARC样本的星系分布。 平面V2kpc-V最后(V2kpc是星系在2 kpc时的旋转速度，V是最外层的)。 我们模拟的星系考虑了重子效应。V2kpc-V上旋转曲线中的散射 平面上，SPARC样品的分布趋势与我们模拟星系的分布基本一致。大 解决“多样性”问题的关键在于重子过程产生非自相似光晕的能力。 只有DM的模拟。我们还发现，重子效应可以再现IC 2574等星系的自转曲线。 以半径上升缓慢为特征的。通过适当的处理，可以得到多样性问题的一个解。 考虑到重子物理效应。
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