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Numerical methods have become a very important type of tool for celestial mechanics, especially in the study of planetary ephemerides. The errors generated during the computation are hard to know beforehand when applying a certain numerical integrator to solve a certain orbit. In that case, it is not easy to design a certain integrator for a certain celestial case when the requirement of accuracy were extremely high or the time-span of the integration were extremely large. Especially when a fixed-step method is applied, the caution and effort it takes would always be tremendous in finding a suitable time-step, because it is about whether the accuracy and time-cost of the final result are acceptable. Thus, finding the best balance between efficiency and accuracy with the least time cost appeared to be a major obstruction in the face of both numerical integrator designers and their users. To solve this problem, we investigate the variation pattern of truncation error and the pattern of rounding error distributions with time-step and time-span of the integration. According to those patterns, we promote an error estimation method that could predict the distribution of rounding errors and the total truncation errors with any time-step at any time-spot with little experimental cost, and test it with the Adams-Cowell method in the calculation of circular periodic orbits. This error estimation method is expected to be applied to the comparison of the performance of different numerical integrators, and also it can be of great help for finding the best solution to certain cases of complex celestial orbits calculations. [ABSTRACT FROM AUTHOR]

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) obs) is significantly different from that of the original orbit ((1 / a) ori), and the peak values are at (1 / a) obs ∼ 2 × 10 − 5 au − 1 and (1 / a) ori ∼ 6 × 10 − 5 au − 1 , respectively; large perihelion LPC (perihelion distance q > 3.1 au) and small perihelion LPC (perihelion distance q ≤ 3.1 au) have the same peak position of original orbit ((1 / a) ori), both located at 1 × 10 − 4 au − 1 ; the peak positions of original reciprocal semi-major axis of LPCs between JPL and MPC are the same, both at 1 × 10 − 4 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. [ABSTRACT FROM AUTHOR]

We study the machine learning method for classifying the basic shape of space debris in both simulated and observed data experiments, where light curves are used as the input features. In the dataset for training and testing, simulated light curves are derived from four types of debris within different shapes and materials. Observed light curves are extracted from Mini-Mega TORTORA (MMT) database which is a publicly accessible source of space object photometric records. The experiments employ the deep convolutional neural network, make comparisons with other machine learning algorithms, and the results show CNN (Convolutional Neural Network) is better. In simulational experiments, both types of cylinder can be distinguished perfectly, and two other types of satellite have around 90% probability to be classified. Rockets and defunct satellites can achieve 99% success rate in binary classification, but in further sub-classes classifications, the rate becomes relatively lower. [ABSTRACT FROM AUTHOR]

The qualitative description of the Neupert effect is that there is a causal relationship between the pulse component (hard X-ray, microwave burst) and the gradual component (soft X-ray emission) in a flare. The initial energy of the flare is released in the form of accelerating particles. The energetic particles produce HXR (hard X-ray) via nonthermal electron-ion bremsstrahlung as they lose their energies in the chromosphere. The SXR (soft X-ray) emission of the flare is the response of energetic particles injected into the chromosphere. According to the quantitative description of the classic Neupert effect, SXR should reach maximum instantly at the end of HXR emission (sign of nonthermal electron injection). However, previous observations have found that for quite a number of flares the SXR peak time (t 2) is significantly later than the end time of HXR (t 1) (τ = t 2 − t 1 , τ > 0), deviating from the classic Neupert effect. In order to study the events deviating from the classic Neupert effect or not, we checked the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) and GOES (Geostationary Operational Environmental Satellites) events list from 2002 to 2015, and found out flare samples that have simple lightcurves at 25–50 keV together with other criteria. A total of 276 flare samples were finally selected. We have analysed the τ distribution of these flares, as well as the relationship between the loop length (represented by the distance between two footpoint sources d) and τ. We found that: (1) 227 sample flares present τ > 0 , which means that about 82% of total samples deviate from the classical Neupert effect; (2) there is a roughly linear correlation between τ and d , that is, the longer the loop is, the later the maximum time of SXR with respect to the end of HXR; (3) there seems to have a critical distance, within which the classic Neupert effect works. These results confirm the necessity of modifying Neupert effect, and expound its physical significance. [ABSTRACT FROM AUTHOR]

The method for precisely determining the astronomical azimuth using the local hour angle (LHA) of Polaris is only applicable in northern middle latitudes. In addition, the meridian star pair method is limited by the conditions of star selection and matching. A new hour angle method for multiple meridian stars is proposed, which is suitable for any part of the global region. When multiple south and north stars have been observed, the influence of longitude error and timing error on the azimuth is modified by linear regression. A precise astronomical position is not required, and there is no limit to the specific position of the meridian stars. Therefore, both the number of observable stars and work efficiency are greatly increased. Our experiment indicates that the results of the new method can reach the first-order accuracy level; i.e., the root mean square error (RMSE) is less than 0.5 ″ , even when the amount of observed data is reduced to half that of the Polaris method. [ABSTRACT FROM AUTHOR]

A sample including 935 blazars with 415 Flat Spectrum Radio Quasars (FSRQs) and 520 BL Lac objects (BL Lacs) (233 HBLs (High synchrotron peak frequency BL Lacs), 144 IBLs (Intermediate synchrotron peak frequency BL Lacs), and 143 LBLs (Low synchrotron peak frequency BL Lacs)) is selected in Fermi 3FGL catalogue. The correlations between two flux densities of the radio 1.4 GHz and γ -ray at 0.1, 0.3, 1, 3, and 10 GeV are investigated for the samples of all blazars, FSRQs, BL Lacs, and subclasses of HBLs and LBLs, respectively. Results show that there are strong positive correlations between the two flux densities, with the correlation coefficients r = 0.48 ∼ 0.81 , and the chance probabilities p all less than 10 − 4. The correlation coefficient has different trends with the change of γ -ray emission frequency for different blazar samples, and the average correlation coefficients for all the samples at five respective bands decrease with the increase of γ -ray frequency. Therefore, with the increase of γ -ray frequency, the dominant mechanism of γ -ray radiation of blazar is changing, and at the same frequency the dominant mechanism is different for different samples. The γ -ray emission of HBLs may be mainly dominated by the synchrotron self-Compton, while the other mechanisms are responsible for the γ -ray emissions of LBLs. The origin of γ -ray in FSRQs is more complex than that of BL Lacs. [ABSTRACT FROM AUTHOR]

Two line element (TLE) released by the North American Aerospace Defense Command (NORAD) is widely used by aerospace workers, and the matched SGP4/SDP4 (Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4) model is used to propagate it. Nevertheless, no corresponding information about its accuracy and covariance is clearly given, thus the application of the TLE data is greatly restricted. In this paper, the determined and predicted orbits are compared to generate the orbit error data, based on the historical TLE data obtained from the Space-Track website and the SGP4/SDP4 model. By dividing different time bins, the fitting coefficients of the variation of orbit prediction error with time are given for each space object, and the characteristics of the error evolution are further discussed for the different types of orbits. The mean analytic model of the orbit prediction error evolution with time is given respectively for the four orbit types of space objects, which provides a valuable reference for extending the application of the TLE data. [ABSTRACT FROM AUTHOR]

A method for the determination of [ α /Fe] from low-resolution stellar spectra is presented. The proposed scheme includes the following three steps: firstly, the spectrum is decomposed by the multi-scale Haar wavelet, and the high-frequency components are removed to suppress the high-frequency noise; then, based on the correlation of the spectral data component with [ α /Fe], the spectral features are selected by the LASSO (Least Absolute Shrinkage and Selection Operator) algorithm; finally, [ α /Fe] is measured by the multiple linear regression method based on the MARCS stellar spectrum library. The effectiveness of the method is verified with the low-resolution stellar spectra of ELODIE, SDSS (Sloan Digital Sky Survey), LAMOST (Large Sky Area Multi-Object Fibre Spectroscopic Telescope), and four star clusters. The systematic deviations and accuracies are as follows: (0.04 dex, 0.064 dex) for the 317 ELODIE spectra; (0.16 dex, 0.065 dex) for the 412 SDSS spectra; (0.05 dex, 0.062 dex) for the 1276 LAMOST spectra (with the signal-noise ratio in the g band (SNRG) greater than 20). The averages of [ α /Fe] obtained for the likely members of the globular star clusters (M13, M15) and open star clusters (NGC2420, M67) are in agreement with the literature values. [ABSTRACT FROM AUTHOR]

Up to now, 17 Neptune Trojan asteroids have been detected with their orbits being well determined by continuous observations. This paper analyzes systematically their orbital dynamics. Our results show that except for two temporary members with relatively short lifespans on Trojan orbits, the vast majority of Neptune Trojans located within their orbital uncertainties may survive in the solar system age. The escaping probability of Neptune Trojans, through slow diffusion in the orbital element space in 4.5 billion years, is estimated to be ∼50%. The asteroid 2012 UW177 classified as a Centaur asteroid by the IAU Minor Planet Center currently is in fact a Neptune Trojan. Numerical simulations indicate that it is librating on the tadpole-shaped orbit around the Neptune's L 4 point. It was captured into the current orbit approximately 0.23 million years ago, and will stay there for at least another 1.3 million years in the future. Its high inclination of i ≈ 54∘ not only makes it the most inclined Neptune Trojan, but also makes it exhibit the complicated and interesting co-orbital transitions between the leading and trailing Trojans via the quasi-satellite orbit phase. [ABSTRACT FROM AUTHOR]

The observational data from radio to X-ray wavebands were collected from the SSDC (Italian Space Agency Science Data Center) for 68 Fermi blazars, and their spectral energy distributions (SEDs) were calculated by means of the least square fitting with a log-parabolic function. Based on the SED fitting parameters, the correlations of the synchrotron peak frequency, curvature and effective spectral index were discussed, and an empirical formula was also proposed to estimate the synchrotron peak frequencies by using the effective spectral indexes. The main results are as follows: (1) From the linear correlation between the synchrotron peak frequency (lg ν p) and the curvature (k), we find that the result supports the energy-dependent acceleration probability model for all BL Lac objects, while the result for the BL Lac objects of lg ν p > 15.3 is consistent with the model of fluctuation of fractional acceleration gain. (2) For the sources of nearly same lg ν p , a significant correlation between the effective spectral index α ro of the radio-optical waveband and the curvature is detected, while the effective spectral index α ox of the optical-x-ray waveband is not correlated with the curvature. According to the effective spectral index α ro , a relation between the synchrotron peak frequency and the curvature can be defined. [ABSTRACT FROM AUTHOR]

Abstract The X-ray emissions of blazars are located at the end of synchrotron radiation and the beginning of inverse Compton radiation. Therefore, the origin of the X-ray emissions is rather complex. The spectral energy distributions (SEDs) of blazars from radio to X-ray bands can be fitted approximatively by a parabolic function. If we consider approximately the fitting curves as the physical spectra of blazars to analyze the X-ray emissions of Fermi blazars, the results show that: (1) The X-ray emissions of blazars contain two components, i.e. the synchrotron radiation and inverse Compton radiation, which can be simply separated by these fitting curves; (2) the higher the synchrotron peak frequency of the source, the greater the synchrotron radiation component, and the less the inverse Compton radiation component; (3) at 1 keV of the X-ray waveband, the synchrotron radiation component accounts for 17%, 27%, and 73% of the total X-ray emission, for FSRQs (Flat Spectrum Radio Quasars), LBLs (Low synchrotron peak frequency BL Lac objects), and HBLs (High synchrotron peak frequency BL Lac objects), respectively; (4) there is a strong positive correlation between the synchrotron peak frequency and the synchrotron radiation flux density at 1 keV, while no correlation exists between the synchrotron peak frequency and the inverse Compton radiation flux density; (5) the radiation mechanism of LBLs may be similar to that of FSRQs in the X-ray waveband. [ABSTRACT FROM AUTHOR]

Abstract A group of successive evolutionary images of a sunspot were observed on 4th March 2014 at the Ca II H (396.85 nm) line by the telescope on board of the Hinode satellite. The calculated oscillation period of the sample point in the umbra is 149.75 s by using the Jurkevich (JK) method. A proper averaged value of the intensity profile is selected as the steady background radiation, then the distribution of the extreme values of oscillations in the umbra is analyzed by a statistical method. The results show that the valley values follow a normal distribution, while the peak values satisfy a partial normal distribution. The distribution of these extreme values indicates that the 3 min oscillation of the umbra may be caused by the propagation of a traveling wave with a period of about 5 min in the umbra. The variation of light intensity caused by the traveling wave may be proportional to the square of the displacement of the traveling wave, resulting in a 3 min period of the light intensity, which is one half of the period of traveling wave. [ABSTRACT FROM AUTHOR]

Abstract The multi-wavelength quasi-simultaneous data of 55 Fermi blazars are fitted by using the conical jet model, and the physical properties of blazar jets are also investigated. Through the X 2-minimization fitting procedure, the best-fit parameters of the conical jet model are obtained. Combined with the other parameters we collected, a statistical analysis is performed. The results of statistical analysis are summarized as follows: (1) The jet power obtained by the spectral energy distribution (SED) fitting is larger than the jet power calculated by using the extended radio luminosity; (2) There is no correlation between the Doppler factor 5 and the magnetic field strength B; (3) There is a correlation between the jet power and the accretion disk luminosity, and the Blandford-Znajek (BZ) mechanism can well explain the energy source of BL Lac jets rather than Flat Spectrum Radio Quasars (FSRQs); (4) The jet power is significantly correlated with the black hole mass. [ABSTRACT FROM AUTHOR]

Abstract The relations between the kinematics of satellites and the properties of hosts and satellites themselves are investigated in this paper. Our sample of hosts and satellites is selected from the Sloan Digital Sky Survey (SDSS) data by adopting a self-adapted method developed by van den Bosch et al. Consistent with the previous studies, the average velocity dispersion increases with the mass of host galaxy, and is larger for red hosts than for blue hosts. We find that, on average, the velocity dispersion is independent of satellite mass around red hosts, however it increases with the satellite mass around blue hosts, and red satellites have a larger velocity dispersion than their blue counterparts. Our further investigations show that in the same halo, the velocity dispersion is independent of satellite mass, regardless of the host color. Interestingly, around red hosts, the red satellites tend to have a smaller velocity dispersion than the blue ones. It implies some interesting processes. In addition, we also find that if host galaxies only have red or blue (high mass or low mass) satellites, the system with red (high mass) satellites has a larger velocity dispersion than that with blue (low mass) satellites. It suggests that satellite properties are important for the measurement of dark halo mass. [ABSTRACT FROM AUTHOR]

In the optical observation of space objects, multiple measurements often occur in the tracking gate, which brings about the uncertainty of tracking measurement and the reduction of tracking accuracy, causes the instability along the tracking path, and eventually leads to the interruption of tracking and the loss of the target. A new approach, combining the Kalman filter and probabilistic data association, is proposed in this paper for the adaptive tracking of space objects. In this method, the gate of association is predicted by the Kalman filter, while the equivalent measurement obtained from the probabilistic data association is adopted as an effective feed. The experiments show that this technique can effectively improve the tracking accuracy as well as the robustness for the automatic tracking of space objects. [ABSTRACT FROM AUTHOR]

Along with the development of the observing technology, the observation and study on the exoplanets’ oblateness and apsidal precession have achieved significant progress. The oblateness of an exoplanet is determined by its interior density profile and rotation period. Between its Love number k 2 and core size exists obviously a negative correlation. So oblateness and k 2 can well constrain its interior structure. Starting from the Lane-Emden equation, the planet models based on different polytropic indices are built. Then the flattening factors are obtained by solving the Wavre's integro-differential equation. The result shows that the smaller the polytropic index, the faster the rotation, and the larger the oblateness. We have selected 469 exoplanets, which have simultaneously the observed or estimated values of radius, mass, and orbit period from the NASA (National Aeronautics and Space Administration) Exoplanet Archive, and calculated their flattening factors under the two assumptions: tidal locking and fixed rotation period of 10.55 hours. The result shows that the flattening factors are too small to be detected under the tidal locking assumption, and that 28% of exoplanets have the flattening factors larger than 0.1 under the fixed rotation period of 10.55 hours. The Love numbers under the different polytropic models are solved by the Zharkov's approach, and the relation between k 2 and core size is discussed. [ABSTRACT FROM AUTHOR]

Time delay and phase fluctuation are produced when the signals of a spacecraft are transmitted through the ionosphere of the earth, which give rise to a great influence on the measurement precision of VLBI (Very Long Baseline Interferometry). Using the 1-year same-beam VLBI data of 2 satellites (Rstar and Vstar) in the Japanese lunar exploration project SELENE, we obtained a model of the relation between the fluctuation of double differential total electron content in the ionosphere and the angular distance of the two satellites. For the 6 baselines, the root mean square r of fluctuation (in units of TECU) and the angular distance of the two satellites θ (in units of ∘ ) has a relation of r = 0 . 773 θ + 0 . 562, and for the 4 VLBI stations, the relation is r = 0 . 554 θ + 0 . 399 from the baselines inversion. The results can serve as a reference for the derivation of differential phase delay and for the occultation observation and study of planetary ionospheres. [ABSTRACT FROM AUTHOR]

A new approach of the initial orbit determination for too-short-arc with angular measurements is implemented by building the probabilistic model in the solution space with the estimation of distribution algorithm. Without any assumption about distribution, the non-parametric kernel density estimation is employed in the model building. The method, unlike other evolutionary algorithms, such as the genetic algorithm and particle swarm optimization, considers the fitness as well as the characteristics of the solution space. Numerical experiments with real observations indicate that without any constraints, the proposed technique has a good performance for the observations of usual accuracy. [ABSTRACT FROM AUTHOR]

By statistically analyzing the masses of twelve double neutron star (DNS) systems, it is concluded that the weighted mean value of DNS masses is (1.339±0.042) M ⊙ , where the weighted mean masses of the primary and companion stars are respectively (1.439±0.036) M ⊙ and (1.239±0.020) M ⊙ . The mean value of the masses of primary stars is higher than that of companion stars, which indicates that the primary star may increase its mass by accretion, or the mass of its progenitor star is higher. Therefore, the physical process of supernova explosion through which the high-mass stars become NSs can be investigated hereby. Also it is found that the total masses of the DNSs span a narrow range of 2.5∼2.8 M ⊙ , implying that the companion stars might impact on the mass formation of DNSs. Moreover, the mass ratios of the DNSs (primaries to companions) approximate 1 (slightly larger than 1), indicating that the masses of the progenitors of primary stars are approximately equal to the masses of the progenitors of companion stars. By analyzing the distribution of the 12 DNSs in the surface magnetic field strength versus spin period ( B-P s ) diagram, it is found that the surface magnetic field strength in the primary stars of the DNSs is ∼ 10 10 Gs, and the spin period is ∼ 50 ms; while the two pulsars, i.e. PSR J1906+0746 and PSR J0737-3039B, are located in the region of normal pulsars in the B-P s diagram, their surface magnetic field strength is ∼ 10 12 Gs, suggesting that they might not be accelerated through accretion. [ABSTRACT FROM AUTHOR]

Deep learning is a typical learning method widely studied in the fields of machine learning, pattern recognition, and artificial intelligence. This work investigates the problem of stellar atmospheric parameterization by constructing a deep neural network with five layers, and the node number in each layer of the network is respectively 3821-500-100-50-1. The proposed scheme is verified on both the real spectra measured by the Sloan Digital Sky Survey (SDSS) and the theoretic spectra computed with the Kurucz's New Opacity Distribution Function (NEWODF) model, to make an automatic estimation for three physical parameters: the effective temperature ( T eff ), surface gravitational acceleration (lg g ), and metallic abundance (Fe/H). The results show that the stacked autoencoder deep neural network has a better accuracy for the estimation. On the SDSS spectra, the mean absolute errors (MAEs) are 79.95 for T eff /K, 0.0058 for (lg T eff /K), 0.1706 for lg ( g /(cm·s −2 )), and 0.1294 dex for the [Fe/H], respectively; On the theoretic spectra, the MAEs are 15.34 for T eff /K, 0.0011 for lg ( T eff /K), 0.0214 for lg( g /(cm · s −2 )), and 0.0121 dex for [Fe/H], respectively. [ABSTRACT FROM AUTHOR]

The multi-task learning takes the multiple tasks together to make analysis and calculation, so as to dig out the correlations among them, and therefore to improve the accuracy of the analyzed results. This kind of methods have been widely applied to the machine learning, pattern recognition, computer vision, and other related fields. This paper investigates the application of multi-task learning in estimating the stellar atmospheric parameters, including the surface temperature ( T eff ), surface gravitational acceleration (lg g ), and chemical abundance ([Fe/H]). Firstly, the spectral features of the three stellar atmospheric parameters are extracted by using the multi-task sparse group Lasso algorithm, then the support vector machine is used to estimate the atmospheric physical parameters. The proposed scheme is evaluated on both the Sloan stellar spectra and the theoretical spectra computed from the Kurucz's New Opacity Distribution Function (NEWODF) model. The mean absolute errors (MAEs) on the Sloan spectra are: 0.0064 for lg ( T eff /K), 0.1622 for lg ( g /(cm · s −2 )), and 0.1221 dex for [Fe/H]; the MAEs on the synthetic spectra are 0.0006 for lg ( T eff /K), 0.0098 for lg ( g /(cm · s −2 )), and 0.0082 dex for [Fe/H]. Experimental results show that the proposed scheme has a rather high accuracy for the estimation of stellar atmospheric parameters. [ABSTRACT FROM AUTHOR]

Solar flares belong to a kind of eruptive phenomena caused by the sudden release of magnetic energy nearby sunspots. It is found that similar flares occurred as well in many Sun-like stars (called as Sun-like star flares). From the data acquired by the Kepler space telescope the SC (Short Cadence) data are mainly selected to make analysis, in order to find the characteristic parameters of light curve profiles of the flares erupted from Sun-like stars for a statistical study, and to summarize the activity features of these stellar flares. The analyzed results show that the light curve profiles and characteristic timescales of the flares of Sun-like stars are quite similar to those of solar flares, which may indicate the same physical mechanism for these two kinds of flares. [ABSTRACT FROM AUTHOR]

Photospheric bright points (PBPs) are tiny short-lived brightening phenomena that can be seen within dark inter-granular lanes. In this paper, we develop a new method to identify and track a PBP in a 3D space-time cube. Different from the common-adopted strategy of “identifying-before-tracking”, this algorithm is based on the strategy of “identifying-by-tracking”. This method can identify a PBP when its intensity is still rather weak, and can avoid the discontinuous evolution of PBP caused by the algorithm of Laplacian morphological dilation (LMD) to recognize completely the evolutionary process of a PBP. The statistics on a group of G-band data observed by Hinode/SOT (Solar Optical Telescope) in quiet regions indicate that the average lifetime of isolated PBP is as long as 3 minutes, and the longest lifetime is up to 27 minutes, which means that the lifetime of PBPs is longer than that obtained by the previous LMD algorithm. Furthermore, it is also found that the mean intensity contrast of PBPs is 1.02 times of the mean photospheric intensity, which is weaker than that calculated by the LMD algorithm, and that the intensity of PBP exhibits a periodical oscillation of 2∼3 minute during the whole lifetime. [ABSTRACT FROM AUTHOR]

In this article, the hydrogen masers in the NTSC (National Time Service Center) timekeeping laboratory are tested. In order to avoid the impact of larger noise of caesium atomic clocks, TA( k) or UTC( k) is not used as reference, instead, the four hydrogen masers are mutually referred and tested. The frequency stability of hydrogen masers is analyzed using the four-cornered hat method, and the Allan standard deviations of each single hydrogen maser in different sample times are estimated. Then, according to the characteristics of hydrogen masers, by removing the trend term, excluding outliers, and smoothing the data with a mathematical method to separate the Gaussian noises of hydrogen masers, and finally by through the Kolmogorov-Smirnov test, the Gaussian noise of each hydrogen maser is estimated. [ABSTRACT FROM AUTHOR]

During the optical observation of space objects, it is difficult to enable the background stars to get matched when the telescope pointing error and tracking error are significant. Based on the idea of decreasing redundancy matching, an effective recognition method for background stars is proposed in this paper. The simulative images under different conditions and the observed images are used to verify the proposed method. The experimental results show that the proposed method has raised the rate of recognition and reduced the time consumption, it can be used to match star patterns accurately and rapidly. [ABSTRACT FROM AUTHOR]

In the data processing of optical space debris observations, the background stars may be mismatched or unable to get matched due to the influence of the telescope pointing error, then it is difficult to calculate the plate model and to determine accurately the object position. Based on the characteristics of debris CCD images, a multiple neighborhood matching method based on feature stars is proposed. The experimental results show that the influence of the telescope pointing error can be removed, and that the efficiency and correctness of background star map matching are improved significantly. Meanwhile, the time cost of this method is low, so it is beneficial to the real-time data reduction. [ABSTRACT FROM AUTHOR]

The multi-task learning approaches have attracted the increasing attention in the fields of machine learning, computer vision, and artificial intelligence. By utilizing the correlations in tasks, learning multiple related tasks simultaneously is better than learning each task independently. An efficient multi-task Lasso (Least Absolute Shrinkage Selection and Operator) regression algorithm is proposed in this paper to estimate the physical parameters of stellar spectra. It not only can obtain the information about the common features of the different physical parameters, but also can preserve effectively their own peculiar features. Experiments were done based on the ELODIE synthetic spectral data simulated with the stellar atmospheric model, and on the SDSS data released by the American large-scale survey Sloan. The estimation precision of our model is better than those of the methods in the related literature, especially for the estimates of the gravitational acceleration (lg g) and the chemical abundance ([Fe/H]). In the experiments we changed the spectral resolution, and applied the noises with different signal-to-noise ratios (SNRs) to the spectral data, so as to illustrate the stability of the model. The results show that the model is influenced by both the resolution and the noise. But the influence of the noise is larger than that of the resolution. In general, the multi-task Lasso regression algorithm is easy to operate, it has a strong stability, and can also improve the overall prediction accuracy of the model. [ABSTRACT FROM AUTHOR]

In the conventional orbit determination with optical measurements of space objects, some observations of different objects may be marked as the same object. For this kind of data, the process of orbit determination will be failed to converge or completely erroneous because of the composition of multiple objects. Here, a method is proposed from the viewing point of maximum likelihood, which combines the orbit improvement and object identification by employing the EM (Expectation Maximum) method, and in the implementation of this method, a robust estimation will be given. Corresponding numerical simulations indicate that this method is feasible, effective, and convenient. [ABSTRACT FROM AUTHOR]

Abstract: The electro-optical tracking of a space object is often interrupted by the dropped frames under the interference of stars. In this paper, the two stages of the tracking process, namely the state extrapolation and real-time sampling, are studied from a probabilistic point of view. Based on the theory of estimation, a new method is proposed, which improves the robustness of prediction by utiliz- ing the data-fusion property of Kalman filtering, and realizes the adjustment of the tracking window by the mean shift technique. The corresponding experiment shows that this method can effectively reduce the impact of interferences, and improve the robustness of the tracking process. [Copyright &y& Elsevier]

Abstract: The BATSE (Compton Gamma-ray Observatory/Bursts and Transient Source Experiment), Swift (Swift Gamma-ray Burst Explorer) and Fermi (Fermi Gamma-ray Space Telescope) satellites have provided us with a large amount of GRB sample. After a systematical study and comparison of the properties of the GRBs detected by these 3 kinds of instruments, it is found that although significant differences exist in the number of red-shifted bursts, the proportion of long bursts in total bursts and the photon flux distribution (lgN − lg P), but no significant difference exists in the duration time, the total flux of Gamma-ray radiation and the spectral hardness ratio. Considering that the observational energy bands of the Swift- and Fermi-detected bursts are different, after making corrections the difference in the lgN − lg P distribution can be basically eliminated. The differences in the number of red-shifted bursts and the proportion of long bursts in total bursts are caused by the different sensitivities of instruments. Namely, various instruments give different observed characteristics of GRBs, but they are consistent in nature. [Copyright &y& Elsevier]

Abstract: In order to study the statistical characters and physical significance of the color indexes and orbital parameters of Centaurs, we have analyzed the color and orbit parameter correlations by using statistical methods according to the known color indexes of 39 Centaurs and their respective orbital parameters. We find that all the correlations of B − V vs. V − R, V − R vs. R − I, B − V vs. R − I and B − R vs. R − I are strong. The Centaurs exhibit obvious redblue double-color property, and the point of demarcation is close to B − R =1.4. The distributions of the various color indexes of Centaurs exhibit the normal distribution. For the correlations between colors and orbital parameters, except for the weak correlations between B − V and the orbital inclination i as well as between V − R and the orbital semi-major axis a, no evident correlation has been found between color indexes and orbital parameters. [Copyright &y& Elsevier]