National Astronomical Observatories Of China Research Articles

A commentary of “Consistency radio bursts in the Milky Way”: 10 remarkable discoveries from 2020 in Nature

The first detection and deep follow-up of a Galactic fast radio burst (FRB) phenomenon were reported in three papers published in the journal Nature in November 2020. Interestingly, this FRB is accompanied by a X-ray burst. The observations from multiple space and ground-based telescopes were combined to accomplish this discovery and ascertain its association with a source in the Milky Way. As the name implies, a FRB is a transient bright pulse of radio waves with a burst duration measured in milliseconds. This phenomenon was first discovered in 2007. It is extremely difficult to detect and even more so to determine their position in the sky due to their brief existence. This is the first detection of a FRB with radiation other than radio waves, as well as the first of its kind in the Milky Way. For the first time, these observations have confirmed that the source(s) of FRBs can be a magnetar(s), which so far is the only verified celestial body capable of producing FRBs. It is worth noting that one of the papers was written by a Chinese research team, the co-first authors of which are Lin Lin from Beijing Normal University, Chunfeng Zhang from Peking University, and Pei Wang from the National Astronomical Observatories of China. The observations came from China's “Sky Eye”—the Five-hundred-meter Aperture Spherical radio Telescope (FAST).①①Original source in Chinese: Di Li, Consistency radio bursts in the Milky Way, Bulletin of National Natural Science Foundation of China. 35 (2) (2021) 243-244.

McatCS: A Highly Efficient Cross-matching Scheme for Multi-band Astronomical Catalogs

Multi-band astronomical catalog cross-matching has always been, and will continue to be, indispensable to astronomy research. However, the archived data volume in different wavebands is extremely huge, which results in the cross-matching process having high computational consumption and slow response. The complexity will also be augmented by the continuous growth of observational data. In this paper, we present mcatCS (multi-band catalog Cross-matching Scheme), a distributed cross-matching scheme to efficiently integrate celestial object data from billion-row multi-band astronomical catalogs. It is deployed on a cluster of commodity machines and provides a command-line-based interface to the end user. To allow fast cross-matching, the data in catalogs are reformatted into the Grouped Spatial Index File, which is a specially designed multi-band catalog uniform format. Furthermore, a min-conflicts data layout strategy is utilized to maximize the parallelization of cross-matching. Using real data, archived in the National Astronomical Observatories of China, we verify that mcatCS has good capabilities for performing efficient and reliable cross-matching between billion-row multi-band catalogs, and experimental results show that the query response speed is 38% to 45% greater than that of MongoDB and 21% to 32% greater than that of PostgreSQL with the HEALPix B-tree index. Moreover, although Q3C and H3C—the extension index packages for PostgreSQL—offer faster query response speed for less than 85 million sources, mcatCS proves to be advantageous after sources scale up to 100 million, and achieves a time reduction of 30.3% and 30.7% compared to Q3C and H3C for 200 million sources.

Internal Variations in Empirical Oxygen Abundances for Giant H ii Regions in the Galaxy NGC 2403

Abstract This paper presents a spectroscopic investigation of 11 regions in the nearby galaxy NGC 2403. The regions are observed with a long-slit spectrograph mounted on the 2.16 m telescope at XingLong station of National Astronomical Observatories of China. For each of the regions, spectra are extracted at different nebular radii along the slit-coverage. Oxygen abundances are empirically estimated from the strong-line indices R23, , , and N2 for each spectrophotometric unit, with both observation- and model-based calibrations adopted into the derivation. Radial profiles of these diversely estimated abundances are drawn for each nebula. In the results, the oxygen abundances separately estimated with the prescriptions on the basis of observations and models, albeit from the same spectral index, systematically deviate from each other; at the same time, the spectral indices R23 and are distributed with flat profiles, whereas N2 and exhibit apparent gradients with the nebular radius. Because our study naturally samples various ionization levels, which inherently decline at larger radii within individual regions, the radial distributions indicate not only the robustness of R23 and against ionization variations but also the sensitivity of N2 and to the ionization parameter. The results in this paper provide observational corroboration of the theoretical prediction about the deviation in the empirical abundance diagnostics. Our future work is planned to investigate metal-poor regions with measurable T e, in an attempt to recalibrate the strong-line indices and consequently disclose the cause of the discrepancies between the empirical oxygen abundances.

Numerical Studies of Astrophysical Objects at Fesenkov Astrophysical Institute (FAI)

Numerical studies of astrophysical objects are a relatively new direction in Fesenkov Astrophysical Institute (FAI) and is mainly represented by the Laboratory of Cosmology, Stellar Dynamics and Computational Astrophysics. The lab seeks to understand the evolution of gravitating systems at various scales – from star clusters to galaxies to large-scale structure of the universe as a whole, and tackles these problems both through analytical methods and through numerical simulations. The particular focus is on numerical simulations of star clusters, especially those found in active galactic nuclei – this is a topic of oldestablished collaboration with colleagues from Astronomisches Rechen-Institut (Heidelberg) and National Astronomical Observatories of China (Beijing). The prominent example is STARDISK project dedicated to the numerical research of active galactic nuclei as multicomponent systems composed of compact stellar cluster, gaseous accretion disk and a supermassive black hole. It is demonstrated that an accretion disk can noticeably decelerate stars and thus enhance the accretion rate onto the black hole. In 2013 FAI hosted the MODEST-13 International Workshop dedicated to modeling of star clusters. Recently a new project has been approved aimed at construction of triaxial equilibrium N-body systems that can be of great help in various numerical experiments with disk galaxies. There are also long standing plans to perform cosmological simulations of large scale structures to test a new approach to dark matter and energy actively developed at FAI. For numerical calculations, FAI has a small, but growing computer cluster consisting of several high-performance computing servers equipped with computational GPU cards.

Pulsations and period variations of the δ Scuti star AN Lyncis in a possible three-body system

Observations for the $\delta$ Scuti star AN Lyn have been made between 2008 and 2016 with the 85-cm telescope at Xinglong station of National Astronomical Observatories of China, the 84-cm telescope at SPM Observatory of Mexico and the Nanshan One meter Wide field Telescope of Xinjiang Observatory of China. Data in $V$ in 50 nights and in $R$ in 34 nights are obtained in total. The bi-site observations from both Xinglong Station and SPM Observatory in 2014 are analyzed with Fourier Decomposition to detect pulsation frequencies. Two independent frequencies are resolved, including one non-radial mode. A number of stellar model tracks are constructed with the MESA code and the fit of frequencies leads to the best-fit model with the stellar mass of $M = 1.70 \pm 0.05~\mathrm{M_{\odot}}$ , the metallicity abundance of $Z = 0.020 \pm 0.001$, the age of $1.33 \pm 0.01$ billion years and the period change rate $1/P\cdot \mathrm{d}P/\mathrm{d}t =1.06 \times 10^{-9} ~\mathrm{yr^{-1}} $, locating the star at the evolutionary stage close to the terminal age main sequence (TAMS). The O-C diagram provides the period change rate of $1/P \cdot \mathrm{d}P /\mathrm{d}t =4.5(8)\times10^{-7}~\mathrm{yr^{-1}}$. However, the period change rate calculated from the models is smaller in two orders than the one derived from the O-C diagram. Together with the sinusoidal function signature, the period variations are regarded to be dominated by the light-travel time effect of the orbital motion of a three-body system with two low-luminosity components, rather than the stellar evolutionary effect.

Automatic detection of solar features in HSOS full-disk solar images using guided filter

A procedure is introduced for the automatic detection of solar features using full-disk solar images from Huairou Solar Observing Station (HSOS), National Astronomical Observatories of China. In image preprocessing, median filter is applied to remove the noises. Guided filter is adopted to enhance the edges of solar features and restrain the solar limb darkening, which is first introduced into the astronomical target detection. Then specific features are detected by Otsu algorithm and further threshold processing technique. Compared with other automatic detection procedures, our procedure has some advantages such as real time and reliability as well as no need of local threshold. Also, it reduces the amount of computation largely, which is benefited from the efficient guided filter algorithm. The procedure has been tested on one month sequences (December 2013) of HSOS full-disk solar images and the result shows that the number of features detected by our procedure is well consistent with the manual one.

Transiting Exoplanet Monitoring Project (TEMP). II. Refined System Parameters and Transit Timing Analysis of HAT-P-33b

Abstract We present 10 R-band photometric observations of eight different transits of the hot Jupiter HAT-P-33b, which has been targeted by our Transiting Exoplanet Monitoring Project. The data were obtained by two telescopes at the Xinglong Station of National Astronomical Observatories of China (NAOC) from 2013 December through 2016 January, and exhibit photometric scatter of . After jointly analyzing the previously published photometric data, radial-velocity (RV) measurements, and our new light curves, we revisit the system parameters and orbital ephemeris for the HAT-P-33b system. Our results are consistent with the published values except for the planet to star radius ratio ( ), the ingress/egress duration (τ) and the total duration (T 14), which together indicate a slightly shallower and shorter transit shape. Our results are based on more complete light curves, whereas the previously published work had only one complete transit light curve. No significant anomalies in Transit Timing Variations (TTVs) are found, and we place upper mass limits on potential perturbers, largely supplanting the loose constraints provided by the extant RV data. The TTV limits are stronger near mean-motion resonances, especially for the low-order commensurabilities. We can exclude the existence of a perturber with mass larger than 0.6, 0.3, 0.5, 0.5, and near the 1:3, 1:2, 2:3, 3:2, and 2:1 resonances, respectively.

The Five‐hundred‐meter Aperture Spherical Radio Telescope project

AbstractThe Five‐hundred‐meter Aperture Spherical Radio Telescope (FAST) is a Chinese megascience project funded by the National Development and Reform Commission (NDRC) of the People's Republic of China. The National Astronomical Observatories of China (NAOC) is in charge of its construction and subsequent operation. Upon its expected completion in September 2016, FAST will surpass the 305 m Arecibo Telescope and the 100 m Green Bank Telescope in terms of absolute sensitivity in the 70 MHz to 3 GHz bands. In this paper, we report on the project, its current status, the key science goals, and plans for early science.

Automatic Recognition of Sunspots in HSOS Full-Disk Solar Images

AbstractA procedure is introduced to recognise sunspots automatically in solar full-disk photosphere images obtained from Huairou Solar Observing Station, National Astronomical Observatories of China. The images are first pre-processed through Gaussian algorithm. Sunspots are then recognised by the morphological Bot-hat operation and Otsu threshold. Wrong selection of sunspots is eliminated by a criterion of sunspot properties. Besides, in order to calculate the sunspots areas and the solar centre, the solar limb is extracted by a procedure using morphological closing and erosion operations and setting an adaptive threshold. Results of sunspot recognition reveal that the number of the sunspots detected by our procedure has a quite good agreement with the manual method. The sunspot recognition rate is 95% and error rate is 1.2%. The sunspot areas calculated by our method have high correlation (95%) with the area data from the United States Air Force/National Oceanic and Atmospheric Administration (USAF/NOAA).

Session 21.3 – Radio and Optical Site Protection

AbstractAdvancement in radio technology means that radio astronomy has to share the radio spectrum with many other non-astronomical activities, majority of which increase radio frequency interference (RFI), and therefore detrimentally affecting the radio observations at the observatory sites. Major radio facilities such as the SKA, in both South Africa and Australia, and the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China will be very sensitive, and therefore require protection against RFI.In the case of optical astronomy, the growing urbanisation and industrialisation led to optical astronomy becoming impossible near major cities due to light and dust pollution. Major optical and IR observatories are forced to be far away in remote areas, where light pollution is not yet extreme. The same is true for radio observatories, which have to be sited away from highly RFI affected areas near populated regions and major cities.In this review, based on the Focus Meeting 21 (FM21) oral presentations at the IAU General Assembly on 11 August 2015, we give an overview of the mechanisms that have evolved to provide statutory protection for radio astronomy observing, successes (e.g at 21 cm HI line), defeats and challenges at other parts of the spectrum. We discuss the available legislative initiatives to protect the radio astronomy sites for large projects like SKA (in Australia and South Africa), and FAST against the RFI. For optical protection, we look at light pollution with examples of its effect at Xinglong observing station of the National Astronomical Observatories of China (NAOC), Ali Observatory in Tibet, and Asiago Observatory in Italy, as well as the effect of conversion from low pressure sodium lighting to LEDs in the County of Hawaii.

Optical Turbulence Characterization by WRF model above Ali, Tibet

Atmospheric optical turbulence modeling and forecast for astronomy is a relatively recent discipline, but has played important roles in site survey, optimization of large telescope observing tables, and in the applications of adaptive optics technique. The numerical approach, by using of meteorological parameters and parameterization of optical turbulence, can provide all the optical turbulence parameters related, such as C2n profile, coherent length, wavefront coherent time, seeing, isoplanatic angle, and so on. This is particularly interesting for searching new sites without the long and expensive site testing campaigns with instruments. Earlier site survey results by the site survey team of National Astronomical Observatories of China imply that the south-west Tibet, Ali, is one of the world best IR and sub-mm site. For searching the best site in Ali area, numerical approach by Weather and Research Forecasting (WRF) model had been used to evaluate the climatology of the optical turbulence. The WRF model is configured over a domain 200km×200km with 1km horizontal resolution and 65 vertical levels from ground to the model top(10millibars) in 2010. The initial and boundary conditions for the model are provided by the 1° × 1° Global Final Analysis data from NCEP. The distribution and seasonal variation of optical turbulence parameters over this area are presented.

Correcting false structures in solar deep-integration magnetogram observations

The real-time correlation solar observation system with a deep integration technique has been operating since 2012 at the Huairou Solar Observation Station at the National Astronomical Observatories of China. However, some magnetograms show false granular structures. After analyzing these images, we believe that the false structures are generated in the last step of the magnetic field measurement: the subtraction of the right circular polarized accumulation image from the left one. Since the left or right image is aligned with the first or second frames by a shift and add technique, separately; the intensity difference between the fields of view (FOV) of the first and second frames cause the false structures. We propose a correction method. Two average FOVs of circular polarized accumulation images are selected as the reference images to replace the first and second frames. Since the average FOVs are determined by the displacement which was calculated and recorded during the alignment procedure, this method can be easily implemented in routine observation procedures. The experimental results prove that our method is successful and effective.

LONG-TERM OPTICAL OBSERVATIONS OF THE Be/X-RAY BINARY X PER

We present the optical spectroscopic observations of X Per from 1999 to 2013 with the 2.16m telescope at Xinglong Station and the 2.4m telescope at Lijiang station, National Astronomical Observatories of China. Combining with the public optical photometric data, we find certain epochs of anti-correlations between the optical brightness and the intensity of the H{\alpha} and HeI 6678 lines, which may be attributed to the mass ejections from the Be star. Alternative explanations are however also possible. The variability of FeII 6317 line in the spectra of X Per might be also caused by the shocked waves formed after the mass ejections from the Be star. The X-ray activities of the system might also be connected with the mass ejection events from the Be star. When the ejected materials were transported from the surface of the Be star to the orbit of neutron star, an X-ray flare could be observed in its X-ray light curves. We use the neutron star as a probe to constrain the motion of the ejected material in the circumstellar disk. With the diffusion time of the ejected material from the surface of Be star to the orbit of neutron star, the viscosity parameter {\alpha} of the circumstellar disk is estimated to be 0.39 and 0.28 for the different time, indicating that the disk around Be star may be truncated by the neutron star at the 2:1 resonance radius and Type I X-ray outburst is unlikely to be observed in X Per.

WW GEMINORUM: AN EARLY B-TYPE ECLIPSING BINARY EVOLVING INTO THE CONTACT PHASE

WW Gem is a B-type eclipsing binary with a period of 1.2378 days. The CCD photometry of this binary was performed in 2013 December using the 85 cm telescope at the Xinglong Stations of the National Astronomical Observatories of China. Using the updated W-D program, the photometric model was deduced from the VRI light curves. The results imply that WW Gem is a near-contact eclipsing binary whose primary component almost fills its Roche lobe. The photometric mass ratio is qph = 0.48(±0.05). All collected times of minimum light, including two newones,wereusedfortheperiodstudies.TheorbitalperiodchangesofWWGemcouldbedescribedbyanupward parabola, possibly overlaid by a light-time orbit with a period of Pmod = 7.41(±0.04)yr and a semi-amplitude of A = 0.0079 days(±0.0005 days), respectively. This kind of cyclic oscillation may be attributed to the light-travel time effect via the third body. The long-term period increases at a rate of dP/dt = +3.47(±0.04) ×10 −8 dayyr −1 , which may be explained by the conserved mass transfer from the less massive component to the more massive one. With mass transfer, the massive binary WW Gem may be evolving into a contact binary.

Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies

In recent years the number of worldwide 8∼10 m-class ground-based telescopes is continually increased, the 4 m-diameter or smaller telescopes have become the small and medium-sized telescopes. In order to obtain some noticeable scientific results by using these existing small and medium-sized telescopes, we have to consider very carefully what we can do, and what we can not. For this reason, the Time Allocation Committee of the 2.16 m telescope of the National Astronomical observatories of China (NAOC) has decided to support some key projects since 2013. The long-term project “Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies” proposed by us is one of three key projects, it is supported by the committee with 30 dark/grey nights in each of three years.The primary goal of this project is to make the spectroscopic observations of the star formation regions along the directions parallel and perpendicular to the main-axes of 20 nearby galaxies with the NAO 2.16 m telescope and the Hec-tospec multi-fiber spectrograph on the 6.5 m MMT (Multiple Mirror Telescope) via the Telescope Access Program (TAP). With the spectra of a large sample of star formation regions, combining with the exising multi-wavelength data from UV to IR, we can study the galaxy dust extinction, star formation rate, metal abundance, and the two-dimensional distributions of stellar population proper-ties, as well as the relationships of the galaxy two-dimensional properties with the galaxy morphologies and environments. As the first paper of this project, we describe here the scientific objectives, sample selection, observation strategy, and present the preliminary result of the spectroscopic observation towards the galaxy NGC 2403.

DEEP, LOW MASS RATIO OVERCONTACT BINARY SYSTEMS. XIII. DZ PISCIUM WITH INTRINSIC LIGHT VARIABILITY

New multi-color photometry for the eclipsing binary DZ Psc was performed in 2011 and 2012 using the 85 cm telescope at the Xinglong Station of the National Astronomical Observatories of China. Using the updated Wilson-Devinney (W-D) code, we deduced two sets of photometric solutions. The overcontact degree is f = 89.7(+/- 1.0)%, identifying DZ Psc as a deep, low mass ratio overcontact binary. The asymmetric light curves (i.e., LC2 in 2012) were modeled by a hot spot on the primary star. Based on all of the available light minimum times, we discovered that the orbital period of DZ Psc may be undergoing a secular period increase with a cyclic variation. The modulated period and semi-amplitude of this oscillation are P-mod = 11.89(+/- 0.19) yr and A = 0.0064(+/- 0.0006) days, which may be possibly attributed to either cyclic magnetic activity or light-time effect due to the third body. The long-term period increases at a rate of dP/dt = +7.43(+/- 0.17) x 10(-7) days yr(-1), which may be interpreted as conserved mass transfer from the less massive component to the more massive one. With mass transferring, DZ Psc will finally merge into a rapid-rotation single star when J(spin)/J(orb) > 1/3.

A new photometry and period analysis of the Algol-type binary XZ And

We present multi-color photometry of the eclipsing binary XZ And, obtained on 2010 October and November with the 60-cm telescope at Xinglong station of National Astronomical Observatories of China. Using the updated W–D program, the photometric elements were deduced from BVR light curves. The results imply that XZ And is a classic Algol-type binary, whose secondary component fills its Roche lobe. The mass ratio and fill-out factor of the primary are q=0.474(±0.003) and f1=68.3(±0.6)%, respectively.Based on photometric and CCD light minimum times, we constructed the O–C curve, which may be described by an upward parabolic line with a quasi-cyclic variation, i.e., light-time orbit. The period and semi-amplitude are Pmod=32.30(±0.06)yr and A=0.d0368(±0.d0008), respectively. This kind of cyclic variation may result from either magnetic activity of the secondary star or light-time effect due to the unseen third body. The long-term period increases at a rate of dP/dt=+5.37(±0.41)×10-7dyr-1, which may be interpreted by the conservative mass transfer from the secondary component to the primary one. With period increasing, the binary may become wider. Finally, XZ And (i.e., 2.15M⊙+1.02M⊙) will transformed into a binary system consisting of a WD and an unevolved companion.

New real-time correlation solar observing system based on GPU for acquiring the deep-integration magnetogram

A real-time correlation solar observing system (RCSOS) has been finished recently at Huairou Solar Observing Station (HSOS) in National Astronomical Observatories of China (NAOC). Graphic Processing Unit (GPU) with Compute Unified Device Architecture (CUDA) parallel programming environment is employed in this system to speed up correlation tracking (CT) process for acquiring deep integration magnetogram and improving the spatial resolution. Observers can choose an interesting area interactively for CT calculation, and then the registration and accumulation of observed images can be processed during the interval period of two images acquisition. In this paper, designing and implementation details of the system are described, and the time costs of all processing modules are analyzed as well. We conclude that the approach is very effective and successful in real-time correlation solar observation at HSOS.

The photometric system of the Tsinghua-NAOC 80-cm telescope at NAOC Xinglong Observatory

The Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at the Xinglong Observatory of NAOC, with the main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations taken on 12 photometric nights, spanning the period from 2004 to 2012, we derived an accurate transformation equation between the instrumental ubvri magnitudes and standard Johnson UBV and Cousins RI magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at the Xinglong Observatory became gradually worse over the period from 2005 to 2012 (e.g., ∼21.4 mag vs. ∼20.1 mag in the V band).

PHOTOMETRIC PROPERTIES FOR SELECTED ALGOL-TYPE BINARIES. V. V1241 TAURI

We present new photometry for the eclipsing binary V1241 Tau, which was obtained on six nights between 2011 December and 2012 January using the 85 cm telescope at the Xinglong station of the National Astronomical Observatories of China. By using the updated Wilson-Devinney code, photometric models with third lights were deduced from two sets of light curves. The result implies that V1241 Tau is an Algol-type near-contact binary (NCB), whose mass ratio and filling-out of the primary are q = 0.545 (± 0.003) and f 1 = 82.4% (± 0.2%), respectively. Based on all available times of minimum light spanning over 80 yr, the O – C curve of V1241 Tau appears to show a quasi-sinusoidal oscillation, i.e., a light-time orbit. The modulated period and amplitude are P mod = 47.4 (± 1.7) yr and A = 0.0087 (± 0.0005) days, respectively. This kind of period variation may be more likely attributed to the light-time effect via a presence of an unseen third body. From an analysis of 23 Algol-type NCBs with EB-type light curves, we determine that the fill-out for the primary f 1 will increase as the orbital period P decreases. With angular momentum loss, the orbit of the binary will shrink, which causes f 1 to increase. The primary component finally fills its Roche lobe, and the binary evolves into contact configuration. Therefore, this kind of Algol-type NCB with EB-type light curves, such as V1241 Tau, may be a progenitor of the A-type W UMa binary.