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International audience; The CHinense Exoplanet Searching Program from Antarctica is a ground-based wide-field photometric survey using the AST3 and CSTAR telescopes located at Dome A, Antarctica. Blessed with the unparalleled observing conditions on the highest point of the Antarctic plateau, three remotely controlled, fully automatic telescopes (AST3-I, AST3-II, and CSTAR-II) carried out continuous high-precision photometric surveys through the polar nights of 2016 and 2017. During the observing seasons of 2016, a total of 26,578 light curves were obtained for stars within the area of the southern continuous viewing zone of TESS, covering an i-band magnitude range from 7.5 to 15. At m i = 10, photometric precision reaches ∼2 mmag, allowing possible discoveries of sub-Jupiter-size exoplanets. Here we report 20 stellar flares with i-band energies larger than 1034 erg detected in the 2016 data set of AST3-II, all from different sources. We model the stellar flares and calculate the durations, amplitudes, energies, and skewnesses. The flare properties and the stellar properties of their sources are presented in this work.

Located at Dome A, the highest point of the Antarctic plateau, the Chinese Kunlun station is considered to be one of the best ground-based photometric sites because of its extremely cold, dry, and stable atmosphere(Saunders et al. 2009). A target can be monitored from there for over 40 days without diurnal interruption during a polar winter. This makes Kunlun station a perfect site to search for short-period transiting exoplanets. Since 2008, an observatory has been built at Kunlun station and three telescopes are working there. Using these telescopes, the AST3 project has been carried out over the last six years with a search for transiting exoplanets as one of its key programs (CHESPA). In the austral winters of 2016 and 2017, a set of target fields in the Southern CVZ of TESS (Ricker et al. 2009) were monitored by the AST3-II telescope. In this paper, we introduce the CHESPA and present the first data release containing photometry of 26,578 bright stars (m_i < 15). The best photometric precision at the optimum magnitude for the survey is around 2 mmag. To demonstrate the data quality, we also present a catalog of 221 variables with a brightness variation greater than 5 mmag from the 2016 data. Among these variables, 179 are newly identified periodic variables not listed in the AAVSO databasea), and 67 are listed in the Candidate Target List(Stassun et al. 2017). These variables will require careful attention to avoid false-positive signals when searching for transiting exoplanets. Dozens of new transiting exoplanet candidates will be also released in a subsequent paper(Zhang et al. 2018b)., 42 pages, 23 figures and 4 tables, ApJS accepted

We report first results from the CHinese Exoplanet Searching Program from Antarctica (CHESPA)---a wide-field high-resolution photometric survey for transiting exoplanets carried out using telescopes of the AST3 (Antarctic Survey Telescopes times 3) project. There are now three telescopes (AST3-I, AST3-II, and CSTAR-II) operating at Dome A---the highest point on the Antarctic Plateau---in a fully automatic and remote mode to exploit the superb observing conditions of the site, and its long and uninterrupted polar nights. The search for transiting exoplanets is one of the key projects for AST3. During the Austral winters of 2016 and 2017 we used the AST3-II telescope to survey a set of target fields near the southern ecliptic pole, falling within the continuous viewing zone of the TESS mission \citep{Ricker10}. The first data release of the 2016 data, including images, catalogs and lightcurves of 26578 bright stars ($7.5\le i \le15$) was presented in \citet{Zhang18}. The best precision, as measured by the RMS of the lightcurves at the optimum magnitude of the survey ($i=10$), is around 2\,mmag. We detect 222 objects with plausible transit signals from these data, 116 of which are plausible transiting exoplanet candidates according to their stellar properties as given by the TESS Input Catalog \citep{Stassun17}, Gaia DR2 \citep{Gaia18} and TESS-HERMES spectroscopy \citep{Sharma18}. With the first data release from TESS expected in late 2018, this candidate list will be a timely for improving the rejection of potential false positives., 49 pages, 23 figures, 3 tables

International audience; From the experiences learned in three decades of exoplanet search, wide-field transit surveys have proven to be one of the most effective ways to detect exoplanets. Wide field of view, however, suffers from high false-positive rates caused by blended eclipsing binaries. The chromaticity in eclipse depth is an effective feature to distinguish low-depth eclipsing binaries from transiting exoplanets, making multiple-band photometry follow-up advantageous before a target is passed onto more expensive spectroscopic follow-up. Moreover, a multiple-band photometric survey is itself a powerful method to find and vet planetary candidates and narrow down the candidate list of high-priority targets. In this work, we report the first results of a dual-band (Sloan-g and -i) wide-field photometry survey—the Chinese Small Telescope ARray II (CSTAR-II), an updated version of the original CSTAR. As a key component of the Chinese Exoplanet Searching Program from Antarctica, CSTAR-II has been tested thoroughly at a remote arctic site near Mohe during the winter of 2014. In total, 13,531 light curves with the best overall photometric precision of ∼3 mmag were extracted from 7721 stars in the Sloan-g and -i bands. Using a robust method, we have detected 63 variables, of which 48 are newly discovered. The dual-band photometric results as well as the stellar properties of the detected sources are provided in this work.

HEPS (Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone (HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M ⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.

Planetary systems can survive the stellar evolution, as evidenced by the atmospheric metal pollution and dusty disks of single white dwarfs. Recent observations show that 1 to 4 percent of single white dwarfs are accompanied by dusty disks, while the occurrence rate of metal pollution is about 25 to 50 percent . The dusty disks and metal pollution have been associated with accretion of remnant planetary systems around white dwarfs, yet the relation between these two phenomena is still unclear. Here we suggest an evolutionary scenario to link the two observational phenomena. By analyzing a sample of metal polluted white dwarfs, we find that the mass accretion rate onto the white dwarf generally follows a broken power law decay, which matches well with the theoretical prediction, if assuming dust accretion is primarily driven by Poynting-Robertson drag and the dust source is primarily delivered via dynamically falling asteroids perturbed by a Jovian planet. The presence of disks is mainly at the early stage (about 0.1 to 0.7 billion years) of the whole process of metal pollution, which is detectable until about 8 billion years, naturally explaining the fraction (about 2-16 percent) of metal-polluted white dwarfs having dusty disks. The success of this scenario also implies that the configuration of an asteroid belt with an outer gas giant might be common around stars of several solar masses., Comment: 33 pages, 3 figures, 10 supplementary figures, 3 supplementary tables. Published in Nature Astronomy

Proxima Centauri is known as the closest star from the Sun. Recently, radial velocity observations revealed the existence of an Earth-mass planet around it. With an orbital period of ~11 days, the surface of Proxima Centauri b is temperate and might be habitable. We took a photometric monitoring campaign to search for its transit, using the Bright Star Survey Telescope at the Zhongshan Station in Antarctica. A transit-like signal appearing on 2016 September 8th, is identified tentatively. Its midtime, $T_{C}=2,457,640.1990\pm0.0017$ HJD, is consistent with the predicted ephemeris based on RV orbit in a 1$\sigma$ confidence interval. Time-correlated noise is pronounced in the light curve of Proxima Centauri, affecting detection of transits. We develop a technique, in a Gaussian process framework, to gauge the statistical significance of potential transit detection. The tentative transit signal reported here, has a confidence level of $2.5\sigma$. Further detection of its periodic signals is necessary to confirm the planetary transit of Proxima Centauri b. We plan to monitor Proxima Centauri in next Polar night at Dome A in Antarctica, taking the advantage of continuous darkness. \citet{Kipping17} reported two tentative transit-like signals of Proxima Centauri b, observed by the Microvariability and Oscillation of Stars space Telescope in 2014 and 2015, respectively. The midtransit time of our detection is 138 minutes later than that predicted by their transit ephemeris. If all the signals are real transits, the misalignment of the epochs plausibly suggests transit timing variations of Proxima Centauri b induced by an outer planet in this system., Comment: 17 pages, 8 figures, 2 tables, accepted by The Astronomical Journal

When single cycle frequency is employed, the existing spectral correlation-signal subspace fitting (SC-SSF) algorithms usually contain two disadvantages: those single-cycle estimators cannot reach the best performance: it is inconvenient to be applied in practice since the right cycle frequency has to be selected. Based on the Jacobi-Anger expansion and the idea of focusing transform, a new approach exploiting multi-cycle frequencies of cyclostationary signal is discussed in this paper. Simulation results demonstrate the effectiveness of the new method.

Previous studies have shown that the neural network approach can be applied to identify defect-prone modules and predict the cumulative number of observed software failures. In this study we examine the effectiveness of the neural network approach in handling dynamic software reliability data overall and present several new findings. Specifically, we find 1. The neural network approach is more appropriate for handling datasets with `smooth' trends than for handling datasets with large fluctuations. 2. The training results are much better than the prediction results in general. 3. The empirical probability density distribution of predicting data resembles that of training data. A neural network can qualitatively predict what it has learned. 4. Due to the essential problems associated with the neural network approach and software reliability data, more often than not, the neural network approach fails to generate satisfactory quantitative results.

The exact compensation for the bias in the classical polar-to-Cartesian conversion is shown to be multiplicative and to depend on the statistics of the cosine of the angle measurement errors. An unbiased conversion is presented. A comparison between this unbiased conversion and the previously presented debiased conversion is made. The unbiased spherical-to-Cartesian conversion is also presented and evaluated.

GAIA leads us to step into a new era with a high astrometry precision of 10 uas. Under such a precision, astrometry will play important roles in detecting and characterizing exoplanets. Specially, we can identify planet pairs in mean motion resonances(MMRs) via astrometry, which constrains the formation and evolution of planetary systems. In accordance with observations, we consider two Jupiters or two super-Earths systems in 1:2, 2:3 and 3:4 MMRs. Our simulations show the false alarm probabilities(FAPs) of a third planet are extremely small while the real two planets can be good fitted with signal-to-noise ratio(SNR)> 3. The probability of reconstructing a resonant system is related with the eccentricities and resonance intensity. Generally, when SNR >= 10, if eccentricities of both planets are larger than 0.01 and the resonance is quite strong, the probabilities to reconstruct the planet pair in MMRs >= 80%. Jupiter pairs in MMRs are reconstructed more easily than super-Earth pairs with similar SNR when we consider the dynamical stability. FAPs are also calculated when we detect planet pairs in or near MMRs. FAPs for 1:2 MMR are largest, i.e., FAPs > 15% when SNR, 22 pages, 18 figures. Published in ApJ

This work is concerned with developing the timedelay-based jamming technology against SAR. Traditional time-delay echo jamming can only get a point or a line false imaging when through the SAR system, which can't protect distributed targets. This paper presents a modified time-delay echo jamming style, Time-delay Inter-pulse Jitter Echo jamming (TDIJEJ). The theoretic analysis and simulation show that this interference can obtain the fast time matched processing gain of SAR thus deduce the jamming power requirement, and generate a jamming swath output for the purpose of protecting distributed targets.

This work is concerned with developing the frequency-based jamming technology against SAR. Firstly, the shift frequency jamming to LFM radar and SAR is analyzed. Then a modified shift frequency jamming to SAR, stepped shift frequency jamming (SSFJ), is presented and discussed. The theoretic research and simulation show that the SSFJ is inter/intra partly coherent with the SAR system and has a region imaging output for protecting the distributed targets. Its jamming power is much less than other jamming styles such as noise jamming, random shift frequency jamming and etc.

The interacting multiple model (IMM) algorithm is combined with the square root unscented Kalman filter (SRUKF), and explored to track maneuvering emitter with a single passive observer, which processes Doppler frequency changing rate and angle measurements concurrently, thus the observer maneuver is not required. Computer simulations are performed to compare the SRUKF based IMM(SRUKF-IMM) tracker with the traditional extended Kalman filter based IMM (EKF-IMM) tracker. Simulation results reveal that the SRUKF-IMM tracker is more stable and effective.

Passive localization by a single observer, is a typical nonlinear and non-Gaussian filtering problem, and often suffers large initial estimation error, low observability and limited achievable measurements. Particle filter provides a means to achieve the state estimation in a nonlinear and non-Gaussian system, however it may be very inefficient when applied to single observe passive localization and tracking (SOPLAT) application. Considering that the measurements' likelihood distribution is more concentrated, a new algorithm of sampling from measurements' likelihood distribution is presented, in which the proposal likelihood distribution is approximated in modified polar coordinate by linear Kalman filtering with the measurements and is used as the proposal for particle filter. Simulation results of comparing the new algorithm with extended Kalman filter (EKF), unscented Kalman filter (UKF) and the EKF and UKF based hybrid particle filter, demonstrate that the new algorithm is superior in convergence speed, tracking precision and filtering stability to others, and the estimation error can approximate the Cramer-Rao lower bound.

The Chinese Small Telescope ARray (CSTAR) has observed an area around the Celestial South Pole at Dome A since 2008. About $20,000$ light curves in the i band were obtained lasting from March to July, 2008. The photometric precision achieves about 4 mmag at i = 7.5 and 20 mmag at i = 12 within a 30 s exposure time. These light curves are analyzed using Lomb--Scargle, Phase Dispersion Minimization, and Box Least Squares methods to search for periodic signals. False positives may appear as a variable signature caused by contaminating stars and the observation mode of CSTAR. Therefore the period and position of each variable candidate are checked to eliminate false positives. Eclipsing binaries are removed by visual inspection, frequency spectrum analysis and locally linear embedding technique. We identify 53 eclipsing binaries in the field of view of CSTAR, containing 24 detached binaries, 8 semi-detached binaries, 18 contact binaries, and 3 ellipsoidal variables. To derive the parameters of these binaries, we use the Eclipsing Binaries via Artificial Intelligence (EBAI) method. The primary and the secondary eclipse timing variations (ETVs) for semi-detached and contact systems are analyzed. Correlated primary and secondary ETVs confirmed by false alarm tests may indicate an unseen perturbing companion. Through ETV analysis, we identify two triple systems (CSTAR J084612.64-883342.9 and CSTAR J220502.55-895206.7). The orbital parameters of the third body in CSTAR J220502.55-895206.7 are derived using a simple dynamical model., 41 pages, 12 figures; published online in ApJS

Based on first-order and second-order phase difference, an algorithm for the modulation recognition is developed in this paper. A method based on instantaneous autocorrelation which can obtain the first-order phase difference is given in this paper, which needn't reveal the phase ambiguity. In order to improve the performance of recognition, N-overlapping phase difference is developed. Several simulations are also conducted and the simulation results indicate the efficiency of the given method

The unscented transformation (UT) based interacting multiple model (IMM) algorithm is explored to handle maneuvering emitter tracking by a single passive observer, which processes Doppler frequency changing rate and angle measurements concurrently, thus the observer maneuver is not required. Computer simulations are performed to compare the unscented kalman filter-interacting multiple model (UKF-IMM) estimator with the traditional extended kalman filter-interacting multiple model (EKF-IMM) estimator. Simulation results reveal that the UKF-IMM estimator is more stable and effective.

Passive location is a widely investigated problem. In this paper, a pseudo-linear algorithm for moving emitters passive location and tracking based on time of arrival (TOA), direction of arrival (DOA) and DOA changing rate measurements by a non-moving observer is given. This algorithm has high convergence speed and stability, so it is of great practicability. The observability conditions of location and tracking for moving emitters using TOA and DOA measurements are analyzed. Finally, the computer simulation results are presented.

A method used for estimation of the position of a moving pulse emitter with constant pulse repeat interval by a single observer is studied. The performance of the estimator depends on the emitter trajectory. A specific trajectory that is symmetrical about the closest point of approach is considered. Under this condition the Fisher information matrix has a simple form. The Cramer-Rao lower bound is then derived. >

The accurate debiasing processing for the bias in the classical conversion mainly depends on the first and second statistics of the cosine of the bearing measurement errors. An unbiased conversion is presented in this paper. Some comparison between the new unbiased conversion with the previously offered debiased conversion is made.

Bearings-only location is a nonlinear estimation problem. The maximum likelihood estimator (MLE) is usually used to obtain the optimal estimate. The MLE is realized by the Newton-Gauss iteration, which only has a local convergence. In this paper a new instrumental variables estimator is developed.

In this paper observability of single passive observer for target motion slate estimation is discussed. Passive observation systems are divided into bearing, time of arrival, Doppler, bearing and time of arrival, bearing and Doppler observation systems. For every type of systems, observability is analyzed in common observation model. The approximate equivalent relation in systems between time difference of arrival and Doppler is shown by comparing their observability degrees.

A radar target classifier based on modular neural networks is presented and its performance compared with that of a classifier based on non-modular neural networks. In this classifier, the response from an unknown target is sent to several waveform predictors that are BP neural networks trained by responses from known targets. The predictor errors are then sent to a classifier using the rule of maximum a posteriori or the rule of modified minimum squared errors. The simulation shows that the new classifier has a good performance on radar target recognition. The method also has other advantages such as easy realization, clear structure and easy expansion.

An array signal model exploiting first-order cyclostationarity of source signals is presented, and an efficient approach to estimate the DOA utilizing the least square (LS) method is developed in this paper. For the cases of single and multiple objects, simulations are made and the results indicate the efficiency of the given method.

For cyclostationary signals, a generalized sensor array data model is presented and a new angle-of-arrival (AOA) estimation method based on weighted cyclic spectrum - GSC-SSF is developed in this paper. The proposed algorithm is more convenient and effective in forming the data matrix or the covariance. matrix for the MUSIC or ESPRIT algorithm to estimate AOA and suppress noise. Simulation results show better performance for the new method.

At present, the feasible and pressing task is to adequately make use of the limited actual data of and human being's limited knowledge on the fight mechanism of radar system vulnerability to ECM (RSVECM) to obtain a better rather than a best solution or objective function to RSVECM directly with the aggregation method. That is, the turning point of the dominance of utilizing the electromagnetic spectrum, and the basic index of radar anti-ECM is the relative improvement factor (RIF) which is determined mainly by the statistical result of computer dynamic course simulation.