Chinese Astronomy and Astrophysics最新文献

Coronal mass ejection (CME) is the large scale magnetized plasmoid ejected from the Sun, which brings huge amount of magnetic flux and plasma into interplanetary space. An earthward CME will interact with the magnetosphere of the Earth, and invokes the substorm and the other phenomena of the space weather as it approaches to the Earth. The 2-dimensional data provided by the current observational techniques cannot describe the true magnetic structure and the plasma distribution of CMEs comprehensively. We need to look into the 3-dimensional structure and the associated three components of CME speeds in order to predict the time when an ICME (Interplanetary CME) reaches the Earth, and the potential consequent impact on the Earth and the nearby environment. In this paper, 3D reconstruction methods of CME based on existing imaging observations are introduced, including two kinds of reconstruction methods based on coronagraph data and heliosphere imager data, and CME-driven shock wave 3D reconstruction methods with high correlation with CME imaging reconstruction. Each method shows apparent advantages in dealing with specific events, but its weakness and necessary constrains to its applications exist as well. Results obtained via various methods are compared in this work, and we found that CME velocities and moving directions deduced from these methods are fairly close to one another, which shows high reliability of these methods. Finally, the hot topics related to the 3-dimensional reconstruction of CME (ICME) and the relevant development in reconstructing methods are also discussed.

The ring focus antenna has special electromagnetic characteristics and application fields. The phase error of ring focus antenna is analyzed theoretically and simulatedly. The phase error caused by the position deviation of the feed and the subreflector, the compensation relationship between the main reflector and subreflector, and the optical path difference caused by the operation of the antenna in holographic measurement are derived. The results will provide theoretical basis and reference for accurate surface measurement and compensation of the ring focus antenna.

The Intra-Group/Cluster Light (IGL/ICL) can be used to study the dynamical evolution of galaxy groups and clusters. Hickson Compact Groups (HCGs) have a high density and a low velocity dispersion, providing a unique environment to study galaxies merger and properties of interacting galaxies. It is also a promising target for the study of IGL. The g and r band deep imaging data of HCG 95 were obtained with Chinese Near Object Survey Telescope (CNEOST). The IGL fraction in HCG 95 is measured with model fitting using GALFIT, giving an IGL fraction (defined by the ratio between the IGL luminosity and the group total luminosity) of 3.55% $\pm$ 0.38% and 3.78% $\pm$ 0.59% in the g and r band, respectively. When applying the surface brightness threshold method, the IGL fraction is 1.9%–10% and 1.5%–10% in the g an r band, respectively. The color of the IGL ($g-r=0.78\pm 0.37$) is similar to that of the HCG 95A and HCG 95C in the group ($g-r=0.82-0.85$), suggesting that it is composed by an old population. It is showed that the IGL in the group may be from the stripped material of interaction between HCG 95A and HCG 95C, with little recent accretion. Combined with the IGL fraction measurements from literatures, we find that the IGL fraction shows no clear correlation with the total mass of groups. A positive correlation is found between the IGL fraction and the early-type galaxies fraction of groups, suggesting that the IGL fraction is linked to the evolutionary stage of a group.

Based on comet observations from JPL (Jet Propulsion Laboratory) and MPC (Minor Planet Center), the orbits of long period comets (LPCs) were reverse-evolved to obtain their original orbits. The dynamic characteristics of LPC observation orbit and original orbit are analyzed. The results show that the distribution of reciprocal of the semi-major axis of LPC observation orbit (${(1/a)}_{\text{obs}}$) is significantly different from that of the original orbit (${(1/a)}_{\text{ori}}$), and the peak values are at ${(1/a)}_{\text{obs}}\sim 2\times {10}^{-5}{\text{au}}^{-1}$ and ${(1/a)}_{\text{ori}}\sim 6\times {10}^{-5}{\text{au}}^{-1}$, respectively; large perihelion LPC (perihelion distance $q>$ 3.1 au) and small perihelion LPC (perihelion distance $q$ $\le$ 3.1 au) have the same peak position of original orbit (${(1/a)}_{\text{ori}}$), both located at $1\times {10}^{-4}{\text{au}}^{-1}$; the peak positions of original reciprocal semi-major axis of LPCs between JPL and MPC are the same, both at $1\times {10}^{-4}{\text{au}}^{-1}$. Many Oort cloud comets have large perihelion distances (more than 50% of comets with $q>$ 3.1 au). It will provide information to understand the dynamical characteristics of long period comets and Oort cloud comets, and will also provide a research basis for future space missions targeting long period comets.

Radio observations of young supernova remnants (SNRs) can shed light on the early evolution of SNRs. We selected G1.9+0.3 which is the youngest SNR in the Milky Way Galaxy for a study. We compiled the radio flux densities currently available and converted them to the same frequency, which leaves us the evolution of the flux density for the past nearly 50 years. We found that the flux density increased before 2008 and decreased afterwards, meaning the flux density reaching the maximum at an age of about 150–155 yr. We attributed the brightening of the SNR to the increase of either magnetic field or the accelerated high energy electrons. Based on the age at which the flux density reached the peak, combined with the previous numerical simulation, we discussed the ejecta mass of the supernova and kinetic energy released by the supernova explosion.

The 1:1 mean motion resonance may be referred to as the lowest order mean motion resonance in restricted or planetary three-body problems. The five well-known libration points of the circular restricted three-body problem are five equilibriums of the 1:1 resonance. Coorbital motion may take different shapes of trajectory. In case of small orbital eccentricities and inclinations, tadpole-shape and horseshoe-shape orbits are well-known. Other 1:1 libration modes different from the elementary ones can exist at moderate or large eccentricities and inclinations. Coorbital objects are not rare in our solar system, for example the Trojans asteroids and the coorbital satellite systems of Saturn. Recently, dozens of coorbital bodies have been identified among the near-Earth asteroids. These coorbital asteroids are believed to transit recurrently between different 1:1 libration modes mainly due to orbital precessions, planetary perturbations, and other possible effects. The Hamiltonian system and the Hill’s three-body problem are two effective approaches to study coorbital motions. To apply the perturbation theory to the Hamiltonian system, standard procedures involve the development of the disturbing function, averaging and normalization, theory of ideal resonance model, secular perturbation theory, etc. Global dynamics of coorbital motion can be revealed by the Hamiltonian approach with a suitable expansion. The Hill’s problem is particularly suitable for the studies on the relative motion of two coorbital bodies during their close encounter. The Hill’s equation derived from the circular restricted three-body problem is well known. However, the general Hill’s problem whose equation of motion takes exactly the same form applies to the non-restricted case where the mass of each body is non-negligible, namely the planetary case. The Hill’s problem can be transformed into a “canonical shape” so that the averaging principle can be applied to construct a secular perturbation theory. Besides the two analytical theories, numerical methods may be consulted, for example the approach of periodic orbit, the surface of section, and the computation of invariant manifolds carried by equilibriums or periodic orbits.

The change of polar motion is closely related to a variety of excitations. These excitations include atmospheric surface pressure and atmospheric wind, seabed pressure and ocean currents, land water distribution, and sea level changes caused by climate warming, and can be estimated by the effective angular momentum function. In the polar motion prediction, the effective angular momentum function is included through the Liouville equation, and combined the least square and autoregressive method for data fitting and extrapolation. At the same time, more options are set for the adjustable parameters of the autoregressive model. In different phases of polar motion prediction, the predictions of each components are matched with optimized parameters, which effectively improves the prediction accuracy of polar motion. In 441 polar motion prediction experiments from 1 to 90 days, the short and medium term predictions were improved more obviously. In the 1–6 day and 7–30 day of the polar motion X (PMX) prediction results, there were 56.9% and 53.5% respectively better than the IERS (International Earth Rotation Service) prediction; in the 1–6 day and 7–30 day of the polar motion Y (PMY) prediction results, 66.5% and 59.7% are better than the IERS prediction, respectively. In General, the performance of PMY prediction is better than that of PMX. Taking IERS EOP (Earth Orientation Parameters) C04 as a reference, the MAE (Mean Absolute Error) of the polar motion X prediction on the 1st-day and 5th-day is improved by 2.6% and 33.0%, respectively compared with the IERS prediction. Compared with the IERS prediction, the MAE of Y prediction on the 1st-day and 5th-day is improved by 20.8% and 49.0%, respectively.

Considering the numerical continuation of periodic solutions, an efficient algorithm is proposed. This algorithm is based on the Broyden’s quasi-Newton method, and is verified by some examples of the periodic solutions of the Brusellator and the planar circular restricted three-body problem (PCRTBP). The Broyden’s method here includes the steps of linear search and the QR (quadrature rectangle) decomposition to solve the linear equations. For the general periodic solutions, the period as a parameter to be continued is included in the periodicity conditions. The period can be used to determine the integration time, then the solution is substituted into the periodicity conditions to get the integral nonlinear equations, which are solved by using the Broyden’s method iteratively until the initial values converge. According to the property that the orbit passing across a hyperplane twice perpendicularly is a symmetric periodic orbit, the interpolation method can be used to obtain the solution components that reach the hyperplane again, and the periodicity conditions are obtained, and then solved by the Broyden’s method. Associating with the symmetry of the Hamiltonian system and some classifications of the periodic orbits of the PCRTBP, a numerical study of the $2/1$, $3/1$ internal resonant periodic solution families is carried out. Finally, the algorithm and calculation results are summarized and discussed.

The ultra-wideband receivers face many technical challenges, and one of the key technical difficulties is the ultra-wideband low-noise amplifier (LNA). Using a gallium arsenide material-based 70 nm gate length metamorphic high electron mobility transistor and dual-supply bias 4-stage amplifier circuit structure, a 4–40 GHz ultra-wideband low-noise monolithic microwave integrated amplifier is designed, which completely covers 5 bands of C, X, Ku, K, and Ka. The design simulation results show that the amplifier gain is (40 $\pm$ 2.5) dB. The average noise temperature at room temperature is 95 K, the noise temperature of 4–12.5 GHz is lower than 83 K in the whole frequency band, and the DC (direct current) power consumption is 130.5 mW. The input reflection coefficient in the entire frequency band is typically - 10 dB, and the output reflection coefficient is typically - 15 dB, stable in the whole frequency range, no self-excited oscillation phenomenon. The device can be used in the ultra-wideband receivers and large-scale multi-beam receivers, which improve the observation efficiency of radio telescopes effectively.

We investigate the molecular gas properties, especially the dense molecular gas in NGC 1614, using the ALMA (Atacama Large Millimeter/ submillimeter Array) high resolution archival data of ${}^{12}$CO(1-0), ${}^{13}$CO(1-0), ${}^{12}$CO(3-2), ${}^{12}$CO(6-5), HCN(3-2), HCO${}^{+}$(3-2), HCN(4-3), and HCO${}^{+}$(4-3). From the high-resolution integrated intensity maps, a ring structure was detected in the central region ($<$ 1 kpc), and the molecular gas mainly distributes in the central region while there is little gas in the nucleus. The ${}^{12}$CO(1-0) shows an extended structure to the south, north, and southeast, and CO ($J⩾3$, $J$ is the quantum number of rotational vibration levels), HCN, and HCO${}^{+}$ show that the dense gas mainly concentrated in the central region. Similarly, HCN(4-3)/${}^{12}$CO(1-0) and HCO${}^{+}$(4-3)/${}^{12}$CO(1-0) ratio maps show that the dense molecular gas is mainly concentrated in the ring of the central region. The HCN/HCO${}^{+}$ ratios show that the different regions of the starburst ring might have different excitation conditions. The variations of HCN/HCO${}^{+}$ values in different region of central region may be due to the gas density and temperature. For HCN/HCO${}^{+}$(4-3) ratio map, the higher intensity values ($\sim$0.44 $\pm$ 0.04) were obtained in the eastern and western region of the ring, compared to the northern and southern region ($\sim$0.35 $\pm$ 0.03). For HCN/HCO${}^{+}$(3-2) ratio map, the higher values ($\sim$0.38 $\pm$ 0.04) are distributed at peak location of HCN(3-2) emission, while the lower values ($\sim$0.3 $\pm$ 0.03) are distributed at the northwestern and southeastern region of the ring. The mechanism of variations of HCN/HCO${}^{+}$