Table of contents

The effective observation of burst events in solar radio research has been impeded by various interference signals, especially interference signals with a wide frequency range and high intensity, as they can partially or completely obscure the observation of burst events. Image processing methods that directly remove the interference signal channels and subtract the average of the interference signal channel are not suitable for processing all types of interference signals. This paper proposes the use of a specific kind of recurrent neural networks, called long short-term memory networks, to predict the value of the radio frequency interference signals with high intensity of the burst event in the solar radio spectrum. The predicted interference can then be removed in accordance with the principle that signals can be linearly added. Therefore, predicted value is subtracted from the data containing the burst event signals and the RFI signals (The radio frequency interference signals to be processed in this article refer to the signal of the broadcast signal that can be received in the frequency range, the signal transmitted by the mobile phone, and the signal transmitted by the sea vessel, and the like) to remove the interference. Then, in order to reduce the error caused by the stepwise prediction in the network and further improve the prediction accuracy, this paper analyzes the characteristics of the value of the radio interference and applies the digital mapping method to convert the prediction problem into the classification problem in the time series. The experimental results show that the proposed method can effectively remove the radio interference in the solar spectrum and clearly show the burst events.

The Square Kilometre Array (SKA) would be the world's largest radio telescope with eventually over a square kilometre of collecting area. However, there are enormous challenges in its data processing. The use of modern distributed computing techniques to solve the problem of massive data processing in the SKA is one of the most important challenges. In this study, basing on the Dask distribution computational framework, and taking the visibility function integral processing as an example, we adopt a multi-level parallelism method to implement distributed averaging over time and channel. Dask Array was used to implement super large matrix or arrays with supported parallelism. To maximize the usage of memory, we further exploit the data parallelism provided by Dask that intelligently distributes the computational load across a network of computer agents and has a built-in fault tolerance mechanism. The validity of the proposed pattern was also verified by using the Common Astronomy Software Application (CASA), wherein we analyze the smearing effects on images reconstructed from different resolution visibilities.

In order to evaluate the ground-based infrared telescope sensitivity affected by the noise from the atmosphere, instruments and detectors, we construct a sensitivity model that can calculate limiting magnitudes and signal-to-noise ratio (S/N). The model is tested with tentative measurements of M'-band sky brightness and atmospheric extinction obtained at the Ali and Daocheng sites. We find that the noise caused by an excellent scientific detector and instruments at −135° C can be ignored compared to the M'-band sky background noise. Thus, when S/N = 3 and total exposure time is 1 second for 10 m telescopes, the magnitude limited by the atmosphere is 13.01^m at Ali and 12.96^m at Daocheng. Even under less-than-ideal circumstances, i.e., the readout noise of a deep cryogenic detector is less than 200e⁻ and the instruments are cooled to below −87.2° C, the above magnitudes decrease by 0.056^m at most. Therefore, according to observational requirements with a large telescope in a given infrared band, astronomers can use this sensitivity model as a tool for guiding site surveys, detector selection and instrumental thermal-control.

The portable adaptive optics (PAO) device is a low-cost and compact system, designed for 4- meter class telescopes that have no adaptive optics (AO) system, because of the physical space limitation at the Nasmyth or Cassegrain focus and the historically high cost of conventional AO. The initial scientific observations of the PAO are focused on the direct imaging of exoplanets and sub-stellar companions. This paper discusses the concept of PAO and the associated high-contrast imaging performance in our recent observational runs. PAO deliver a Strehl ratio better than 60% in H band under median seeing conditions of 1''. Combined with our dedicated image rotation and subtraction (IRS) technique and the optimized IRS (O-IRS) algorithm, the averaged contrast ratio for a 5 ≤ V_mag ≤ 9 primary star is 1.3 × 10⁻⁵ and 3.3 × 10⁻⁶ at angular distance of 0.36'' with exposure time of 7 minutes and 2 hours, respectively. PAO has successfully revealed the known exoplanet of κ And b in our recent observation with the 3.5-meter ARC telescope at Apache Point Observatory. We have performed the associated astrometry and photometry analysis of the recovered κ And b planet, which gives a projected separation of 0.984'' ± 0.05'', a position angle of 51.1° ± 0.5° and a mass of ${10.15}_{-1.255}^{+2.19}{M}_{{\rm{Jup}}}$. These results demonstrate that PAO can be used for direct imaging of exoplanets with medium-sized telescopes.

Making use of quasar spectra from LAMOST, in the spectral data around the Mg ii emission lines, research described in this paper has detected 217 Mg ii narrow absorption lines (NALs) with ${W}_{r}^{\lambda 2796}\ge 3{\sigma }_{w}$ and ${W}_{r}^{\lambda 2803}\ge 2{\sigma }_{w}$ in a redshift range of 0.4554 ≤ z_abs ≤ 2.1110. For quasars observed by both LAMOST and SDSS, we find that 135 Mg ii NALs were obviously observed in the LAMOST spectra, 347 Mg ii NALs were were apparent in the SDSS spectra, and 132 Mg ii NALs were clearly present in both the SDSS and LAMOST spectra. The missed Mg ii NALs are likely ascribed to low signal-to-noise ratios of corresponding spectra. Among the Mg ii NALs obviously observed in SDSS or LAMOST spectra, eight Mg ii NALs were significantly changed with $|\Delta {W}_{r}^{\lambda 2796}|\ge 3{\sigma }_{w}$ in time intervals of Δ MJD/(1 + z_em) = 359 – 2819 d.

In this paper, we present four sets of photometric V RI light curves, and several LAMOST low and medium resolution spectra of contact binary CC Com. We revised the orbital parameters by simultaneously combining with previously published radial velocity measurements using the Wilson-Devinney program. We used light curves at different observational times to obtain the starspot parameters. The values of the starspot radius are variable in short- and long-term scales, and their longitudes are stable. We updated the orbital period change of CC Com, and analyzed the periodic variation. The period of CC Com decreases at a rate of 4.66 (±0.20) × 10⁻¹¹ d yr⁻¹, which may be due to mass transfer from the secondary component to the primary component. The oscillation of its orbital period with a period of 17.18(0.08) years and amplitude of 0.0018(1) d may be caused by the light time effect (LITE) via a third body of 0.06 M_⊙ dwarf or magnetic activity cycle. Furthermore, we obtained one optical spectrum from the LAMOST survey, which gives the spectral type of CC Com as K7±2V. Strong emissions exist in the Hα, and Ca ii H&K lines in the observed spectrum, indicating strong chromospheric activity on CC Com. In the 12 LAMOST medium-resolution spectra, the EWs of Hα line are variable along the phase and time, which may be a plage or flare event.

The very low frequency (VLF) regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources, transients, and so on. However, the nontransparency of the Earth's ionosphere, ionospheric distortion and artificial radio frequency interference (RFI) have made it difficult to detect the VLF celestial radio emission with ground-based instruments. A straightforward solution to overcome these problems is a space-based VLF radio telescope, just like the VLF radio instruments onboard the Chang'E-4 spacecraft. But building such a space telescope would be inevitably costly and technically challenging. The alternative approach would be then a ground-based VLF radio telescope. Particularly, in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a 'calm' state, it will provide us a good chance to perform VLF ground-based radio observations. Anticipating such an opportunity, we built an agile VLF radio spectrum explorer co-located with the currently operationalMingantu Spectra Radio Heliograph (MUSER). The instrument includes four antennas operating in the VLF frequency range 1–70 MHz. Along with them, we employ an eight-channel analog and digital receivers to amplify, digitize and process the radio signals received by the antennas. We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.

Scattering of anisotropic radiation by atoms, ions or molecules is sufficient to generate linear polarization observable in stars' and planets' atmospheres, circumstellar environments, and in particular in the Sun's atmosphere. This kind of polarization is called scattering polarization (SP) or second solar spectrum (SSS) if it is formed near the limb of the solar photosphere. Generation of linear SP can typically be reached more easily than circular SP. Interestingly, the latter is often absent in observations and theories. Intrigued by this, we propose to demonstrate how circular SP can be created by anisotropic collisions if a magnetic field is present. We also demonstrate how anisotropic collisions can result in the creation of circular SP if the radiation field is anisotropic. We show that under certain conditions, linear SP creation is accompanied by the emergence of circular SP which can be useful for diagnostics of solar and astrophysical plasmas. We treat an example and calculate the density matrix elements of tensorial order k = 1 which are directly associated with the presence of circular SP. This work should encourage theoretical and observational research to be increasingly oriented towards circular SP profiles in addition to linear SP in order to improve our analysis tools of astrophysical and solar observations.

In the work presented here, the impact of magnetic field on the dynamical evolution of cometary globules Sim 129 and Sim 130 in the Sh2-236 HII region and the ionized gas streaming out of their surfaces is investigated. The magnetic field morphology in the region associated with these globules is inferred using optical polarization measurements with the Sampurnanand Telescope at ARIES. The nebular emission is probed through radio continuum mapping at 1.4 GHz with the archival National Radio Astronomy Observatory (NRAO) Very Large Array (VLA) Sky Survey (NVSS) data. The correlation of these measurements suggests that photoevaporated gas from the surfaces of Sim 129 and Sim 130 accumulates in clouds and starts streaming along the magnetic field lines. The ¹²CO (J=1–0) molecular line observations are performed towards NGC 1893 from the 14-m single dish radio telescope in Taeduk Radio Astronomy Observatory (TRAO). The velocity dispersion in the ¹²CO (J=1–0) molecular line and the dispersion in polarization angles are considered in the Davis-Chandrasekhar-Fermi formulation to estimate the magnetic field strength towards two Sim nebulae. The average value of field strength is found to be ∼60 μG with uncertainty of 0.5 times the estimated value.

Phased array feeds (PAFs), which illuminate the dish with digitally synthesized beams instead of separated horns, provide the capability for wider and continuous field-of-view surveys. As a promising technology for next generation radio telescopes, PAFs will provide the Qi Tai Telescope (QTT), which will be next world-class fully steerable radio telescope, an opportunity of reaching several cutting-edge science goals. This paper presents a brief introduction of the wideband PAF for QTT, and the detailed design and simulation of the cryogenic system. Based on this design, a scaled prototype of the spherical vacuum window, which is the key part of the cryogenic system, has been built and the performance is verified.

A new method of light curve inversion with bipartite regularization (LIBR), which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio, is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1- Q17 data set. The Markov Chain Monte Carlo (MCMC) method was applied to find the best profile of the reconstructed surface. The known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 d. Because of the nature of the light curve inversion, the spot model is limited to the equatorial region. We also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC method. Combined with the LIBR inversion results, it was found that the star spots typically last from one to several stellar rotations. From the time evolution of the spot size, a magnetic cycle period of 437 d can be derived. This value is comparatively shorter than the solar cycle which might be a consequence of the younger age (∼ 1.78 Gyr) of Kepler-17. The light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare activity. An interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter, Kepler-17b, via a lower-level energy release process.

We apply the jet-powered ILOT scenario to two recently studied intermediate luminosity optical transients (ILOTs), and find the relevant shell mass and jets' energy that might account for the outbursts of these ILOTs. In the jet-powered ILOT scenario, an accretion disk around one of the stars of a binary system launches jets. The interaction of the jets with a previously ejected slow shell converts kinetic energy to thermal energy, part of which is radiated away. We apply two models of the jet-powered ILOT scenario. In the spherical shell model, the jets accelerate a spherical shell, while in the cocoon toy model the jets penetrate into the shell and inflate hot bubbles, the cocoons. We find consistent results. For the ILOT (ILRT: intermediate luminosity red transient) SNhunt120 we find the shell mass and jets' energy to be M_s ≃ 0.5 − 1 M_⊙ and E_2j ≃ 5 × 10⁴⁷ erg, respectively. The jets' half opening angle is α_j ≃ 30° − 60°. For the second peak of the ILOT (luminous red nova) AT 2014ej we find these quantities to be M_s ≃ 1 − 2 M_⊙ and E_2j ≃ 1.5 × 10⁴⁸ erg, with α_j ≃ 20° − 30°. The models cannot tell whether these ILOTs were powered by a stellar merger that leaves one star, or by mass transfer where both stars survived. In both cases the masses of the shells and energies of the jets suggest that the binary progenitor system was massive, with a combined mass of M₁ + M₂ ≳ 10 M_⊙.

High resolution imaging of inner jets in Active Galactic Nuclei (AGNs) with Very Long Baseline Interferometry (VLBI) at millimeter wavelengths provides deep insight into the launching and collimation mechanisms of relativistic jets. The BL Lac object, PKS 1749+096, shows a core-dominated jet pointing toward the northeast on parsec-scales revealed by various VLBI observations. In order to investigate the jet kinematics, in particular, the orientation of the inner jet on the smallest accessible scales and the basic physical conditions of the core, in this work we adopted a super-resolution technique, the Bi-Spectrum Maximum Entropy Method (BSMEM), to reanalyze VLBI images based on the Very Long Baseline Array (VLBA) observations of PKS 1749+096within the VLBA-BU-BLAZAR 7mm monitoring program. These observations include a total of 105 epochs covering the period from 2009 to 2019. We found that the stacked image of the inner jet is limb-brightened with an apparent opening angle of 50 ° 0 ± 8 ° 0 and 42 ° 0 ± 6° 0 at the distances of 0.2 and 0.3 mas (0.9 and 1.4 pc) from the core, corresponding to an intrinsic jet opening angle of 5° 2 ± 1 ° 0 and 4° 3 ± 0° 7, respectively. In addition, our images show a clear jet position angle swing in \sr within the last ten years. We discuss the possible implications of jet limb brightening and the connection of the position angle with jet peak flux density and gamma-ray brightness.

The Chinese Space Station Telescope (CSST) spectroscopic survey plans to deliver high-quality low-resolution (R > 200) slitless spectra for hundreds of millions of targets down to a limiting magnitude of about 21 mag, covering a large survey area (17 500 deg²) and a wide wavelength range (255–1000 nm by three bands GU, GV, and GI). In this work, we use empirical spectra of the Next Generation Spectral Library to simulate the CSST stellar spectra at R = 250, and investigate their capabilities in measuring radial velocities. We find that velocity uncertainties depend strongly on effective temperature, weakly on metallicity for only FGK stars, and hardly on surface gravity. It is possible to deliver stellar radial velocities to a precision of about 3 km s⁻¹ for AFGKM stars, and about 10 km s⁻¹ for OB stars, at signal-to-noise ratio (SNR) of 100. Velocity uncertainties using single GU/GV/GI band spectra are also explored. Given the same SNR, the GU band performs best, the GV band the second best, and then the GI band. The effects of spectral normalization and the imperfect template on velocity measurements are investigated and found to be very weak. The uncertainties caused by wavelength calibration are considered and found to be moderate. Given the possible precision of radial velocities, the CSST spectroscopic survey can enable interesting science such as searching for hyper-velocity stars. Limitations of our results are also discussed.

Based on astrometric data from Gaia Data-Release 2 (DR2), we employ an unsupervised machine learning method to blindly search for open star clusters in the Milky Way within the Galactic latitude range of |b| < 20°. In addition to 2080 known clusters, 74 new open cluster candidates are found. In this work, we present the positions, apparent radii, parallaxes, proper motions and member stars of these candidates. Meanwhile, to obtain the physical parameters of each candidate cluster, stellar isochrones are fit to the photometric data. The results show that the apparent radii and the observed proper motion dispersions of these new candidates are consistent with those of open clusters previously identified in Gaia DR2.

We consider the problem of predicting the mid-term daily 10.7cm solar radio flux (F10.7), a widely-used solar activity index. A novel approach is proposed for this task, in which BoxCox transformation with a proper parameter is first applied to make the data satisfy the property of homoscedasticity that is a basic assumption of regression models, and then a multi-output linear regression model is used to predict future F10.7 values. The experiment shows that the BoxCox transformation significantly improves the predictive performance and our new approach works substantially better than the prediction from the US Airforce and other alternative methods like Auto-regressiveModel, Multi-layer Perceptron, and Support Vector Regression.

The change of sound speed has been found at the base of the convection during the solar cycles, which can be used to constrain the solar internal magnetic field. We aim to check whether the magnetic field generated by the solar dynamo can lead to the cyclic variation of the sound speed detected through helioseismology. The basic configuration of magnetic field in the solar interior was obtained by using a Babcock-Leighton (BL) type flux transport dynamo. We reconstructed one-dimensional solar models by assimilating magnetic field generated by an established dynamo and examined their influences on the structural variables. The results show that magnetic field generated by the dynamo is able to cause noticeable change of the sound speed profile at the base of the convective zone during a solar cycle. Detailed features of this theoretical prediction are also similar to those of the helioseismic results in solar cycle 23 by adjusting the free parameters of the dynamo model.

Since Sep. 2018, LAMOST has started the medium-resolution (R ∼ 7500) spectral survey (MRS). We proposed the spectral survey of Galactic nebulae, including H ii regions, HH objects, supernova remnants, planetary nebulae and the special stars with MRS (LAMOST MRS-N). LAMOST MRS-N covers about 1700 square degrees of the northern Galactic plane within 40° < l < 215° and –5° < b < 5°. In this 5-year survey, we plan to observe about 500 thousand nebulae spectra. According to the commissioning observations, the nebulae spectra can provide precise radial velocity with uncertainty less than 1 km s⁻¹. These high-precision spectral data are of great significance to our understanding of star formation and evolution.

Considering the importance of investigating the transit timing variations (TTVs) of transiting exoplanets, we present a follow-up study of HAT-P-12b. We include six new light curves observed between 2011 and 2015 from three different observatories, in association with 25 light curves taken from the published literature. The sample of the data used thus covers a time span of ∼ 10.2 years with a large coverage of epochs (1160) for the transiting events of the exoplanet HAT-P-12b. The light curves are utilized to determine the orbital parameters and conduct an investigation of possible TTVs. The new linear ephemeris shows a large value of reduced χ², i.e. ${\chi }_{{\rm{red}}}^{2}(23)$ = 7.93, and the sinusoidal fitting using the prominent frequency coming from a periodogram shows a reduced χ² around 4. Based on these values and the corresponding O – C diagrams, we suspect the presence of a possible non-sinusoidal TTV in this planetary system. Finally, we find that a scenario with an additional non-transiting exoplanet could explain this TTV with an even smaller reduced χ² value of around 2.

This paper introduces a technique for searching for bright massive stars in galaxies beyond the Local Group. To search for massive stars, we processed the results of stellar photometry from the Hubble Space Telescope (HST) images using the DAOPHOT and DOLPHOT packages. The results of such searches are demonstrated with examples of the galaxies DDO 68, M94 and NGC 1672. In the galaxy DDO 68, the LBV star changes its brightness, and massive stars in M94 can be identified by excess in the Hα band. For the galaxy NGC 1672, we measure the distance for the first time by the TRGB method, which enabled determining the luminosities of the brightest stars, likely hypergiants, in the young star formation region. So far, we have performed stellar photometry on HST images of 320 northern sky galaxies located at a distance less than 12 Mpc. This allowed us to identify 53 galaxies with probable hypergiants. Further photometric and spectral observations of these galaxies are planned to search for massive stars.

In this work, we train three decision-tree based ensemble machine learning algorithms (Random Forest Classifier, Adaptive Boosting and Gradient Boosting Decision Tree respectively) to study quasar selection in the variable source catalog in SDSS Stripe 82. We build training and test samples (both containing 1:1 of quasars and stars) using the spectroscopic confirmed sources in SDSS DR14 (including 8330 quasars and 3966 stars). We find that when trained with variation parameters alone, all three models can select quasars with similarly and remarkably high precision and completeness (∼ 98.5% and 97.5%), even better than trained with SDSS colors alone (∼ 97.2% and 96.5%), consistent with previous studies. By applying the trained models on the variable sources without spectroscopic identifications, we estimate the spectroscopically confirmed quasar sample in Stripe 82 variable source catalog is ∼ 93% complete (95% for m_i < 19.0). Using the Random Forest Classifier we derive the relative importance of the observational features utilized for classifications. We further show that even using one- or two-year time domain observations, variability-based quasar selection could still be highly efficient.

We present the first HI 21 cm spectroscopy detection of J030417.78+002827.4, which is an active galactic nucleus (AGN) with an intermediate-mass black hole (IMBH) in the center. The observations were carried out with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) last year. We relied on the ON-OFF observing approach with the 19-beam receiver covering 1.05 – 1.45 GHz. Within a total integration time of about 20 min, the root mean square (RMS) of our data reaches 1.2 mJy beam⁻¹, at a velocity resolution of 1.6 kms. Radio frequency interference (RFI) is checked and excluded during the data analysis. The detected HI spectroscopy shows a dual-horned profile with a line width of 223.5 kms, indicating gas rotation around this AGN. The redshift of this galaxy derived from our HI observation is 0.0447. We calculate the atomic gas mass by the integrated flux of the HI emission line. The total gas mass in this galaxy is estimated to be 1.8 × 10¹⁰M_⊙. We find the fraction of gas-to-stellar mass ratio in J030417.78+002827.4 is more than 50%. This ratio is much higher than the typical value found in other AGNs with supermassive black holes (SMBHs), and is comparable to some star-forming galaxies recently observed by FAST.

Deconvolution is used to eliminate imperfections in the point spread function, such as sidelobes caused by incomplete sampling of radio telescopes, and is a key technology for radio synthesis imaging. Modern telescopes have such high sensitivities that the observed celestial images may contain both compact and diffuse emission. This essentially requires deconvolution technology to have the ability to model both. In this paper, a deconvolution algorithm based on hybrid parameterization is proposed for the rapid reconstruction of complex celestial structures. In this algorithm, scale-free parameterization is utilized to reconstruct compact emission, while multi-scale parameterization is employed to reconstruct diffuse emission. Simulated data representing Square Kilometre Array (SKA) observations with realistic celestial brightness distributions are applied to test the performance of the algorithm. Our experiments show that, compared with other state-of-the-art deconvolution algorithms, the algorithm proposed in this paper can reconstruct complex celestial structures well and provide competitive reconstruction results while greatly improving the reconstruction speed.

S5 0716+714 and 3C 273 are frequently studied blazars, which show obvious optical variabilities with different timescales. Using the 1.0 m telescope at the Yunnan Observatory, we monitored the two sources. For S5 0716+714, we report 990 observations during the monitoring duration from JD 2458536 to JD 2458540. For 3C 273, there are 884 observations during the monitoring duration from JD 2458539 to JD 2458542. Based on those observations, we obtain the following results. (1) For S5 0716+714, there lie intra-day optical variabilities (IDVs), with timescales from 0.31 hours to 2.64 hours. For 3C 273, it is possible that there lie IDVs, with timescales from 0.36 hours to 0.49 hours. (2) The time delay of S5 0716+714 is τ_RI = 3.46 min between R and I bands, and the time delay of 3C273 is τ_IV = 6.42 min between I and V bands. (3) We find that, for S5 0716+714, there lies a suspected intra-day period, P ≈ 185.78 min; for 3C 273, there lie intra-day periods, which are about ∼60 min and ∼80 min.

It is well known that a flat radio spectrum is a common property in the spectral energy distribution of blazars. Although one-zone leptonic models are generally successful in explaining the multi-wave band emission, they are problematic in reproducing the radio spectrum. In the study of Mrk 421, one-zone models suggest that in order to avoid overproducing the radio flux, the minimum electron Lorentz factor should be larger than a few hundred at least, even considering the synchrotron self-absorption effect. This result suggests that the model predicted spectral index in the radio band of Mrk 421 should be -1/3. On the basis of this result, by assuming there is a neglected region that will also contribute the radio emission and its electron energy index naturally originates from the simplest first-order Fermi acceleration mechanism, we can get a superimposed flat radio spectrum. In this paper, a two-zone model is proposed to reproduce the quiescent state spectral energy distribution of Mrk 421. In addition to taking into account the emission from a conventional radiation zone, we further consider emission from the acceleration zone in which particles are accelerated at a shock front. With the present model, our fitting result suggests that the low frequency flat radio spectrum of Mrk 421 might be explained as a superposition of the synchrotron emission from acceleration zone and radiation zone.

The complete orbital and spin period evolutions of the double neutron star (NS) system PSR J0737–3039 are simulated from birth to coalescence, which include the two observed radio pulsars classified as primary NS PSR J0737–3039A and companion NS PSR J0737–3039B. By employing the characteristic age of PSR J0737–3039B to constrain the true age of the double pulsar system, the initial orbital period and initial binary separation are obtained as 2.89 h and 1.44 × 10⁶ km, respectively, and the coalescence age or the lifetime from the birth to merger of PSR J0737–3039 is obtained to be 1.38 × 10⁸ yr. At the last minute of coalescence, corresponding to the gravitational wave frequency changing from 20 Hz to 1180 Hz, we present the binary separation of PSR J0737–3039 to be from 442 km to 30 km, while the spin periods of PSR J0737–3039A and PSR J0737–3039B are 27.10 ms and 4.63 s, respectively. From the standard radio pulsar emission model, before the system merged, the primary NS could still be observed by a radio telescope, but the companion NS had crossed the death line in the pulsar magnetic-field versus period (B – P) diagram at which point it is usually considered to cease life as a pulsar. This is the first time that the whole life evolutionary simulation of the orbit and spin periods for a double NS system is presented, which provides useful information for observing a primary NS at the coalescence stage.

In this paper, we report the observed temporal correlation between extreme-ultraviolet (EUV) emission and magneto-acoustic oscillations in an EUV moss region, which is the footpoint region only connected by magnetic loops with million-degree plasma. The result is obtained from a detailed multi-wavelength data analysis of the region with the purpose of resolving fine-scale mass and energy flows that come from the photosphere, pass through the chromosphere and finally heat the solar transition region or the corona. The data set covers three atmospheric levels on the Sun, consisting of high-resolution broad-band imaging at TiO 7057 Å and the line of sight magnetograms for the photosphere, high-resolution narrow-band images at helium i 10830 Å for the chromosphere and EUV images at 171 Å for the corona. The 10830 Å narrow-band images and the TiO 7057 Å broad-band images are from a much earlier observation on 2012 July 22 with the 1.6 meter aperture Goode Solar Telescope (GST) at Big Bear Solar Observatory (BBSO) and the EUV 171 Å images and the magnetograms are from observations made by Atmospheric Imaging Assembly (AIA) or Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We report the following new phenomena: (1) Repeated injections of chromospheric material appearing as 10830 Å absorption are squirted out from inter-granular lanes with a period of ∼ 5 minutes. (2) EUV emissions are found to be periodically modulated with similar periods of ∼ 5 minutes. (3) Around the injection area where 10830 Å absorption is enhanced, both EUV emissions and strength of the magnetic field are remarkably stronger. (4) The peaks on the time profile of the EUV emissions are found to be in sync with oscillatory peaks of the stronger magnetic field in the region. These findings may give a series of strong evidences supporting the scenario that coronal heating is powered by magneto-acoustic waves.

In the present work, we study the time evolution, significance of the N-S asymmetry excesses presented as a function of the solar cycle and prominent rotational periods (∼27 d) separately for the northern and southern hemispheres. We have investigated short-term variations of the hemispheric solar activity (sunspot numbers and sunspot areas) during the time period 2010–2015, which covers the ascending and the maximum phase of solar cycle 24. We have implemented the Lomb-Scargle periodogram and continuous wavelet transform power spectrum techniques to study the time evolution and dominant rotational periods separately for the northern and southern hemispheres, and whole solar disk. Our results showed that the northern hemisphere exhibited longer solar synodic periods than the southern hemisphere, indicating that the northern hemisphere has a lower rotation rate. Moreover, the northern hemisphere was found to be dominant before transferring to the southern hemisphere during mid-2013. Also, the sunspot areas clearly demonstrated a two-peak structure of solar activity in the northern and southern hemispheres respectively during 2012 and 2014. The statistical significance of the southern hemisphere affirmed enhanced excess during the maximum phase of solar cycle 24.