Celestial Coordinates Research Articles

Statistical Analysis on the Number of Discoveries and Discovery Scenarios of Near-Earth Asteroids

Near-Earth asteroids (NEAs) are a kind of small solar system bodies that may lead to potential hazard to the safety of the Earth. Currently, most of the NEAs are discovered with ground-based telescopes and the number is still growing. In order to provide references and experience to our future near-Earth asteroid discovery and monitoring, we perform a multi-dimensionally statistical analysis on the discovery data of NEAs with public database obtained from the website of Minor Planet Center (MPC). We find the constraint of observation ability can lead to selection effect on the discoveries, which causes a yearly dependence trend and a size-dependence characteristic of the relative proportion for different orbit types of discovered NEAs. Besides, combined with the orbits obtained from numerical simulations, we revisit the discovery scenarios of these objects. The position distribution of the objects under different celestial coordinate systems are obtained, and the dependence on seasons, observatory latitudes, and the diameters are analyzed. Finally, we quantify the impact of the Sun, the Moon, and the galactic plane on the discoveries by analyzing the observation data, and find that ground-based telescopes generally have difficulty in discovering NEAs within 90∘ from the Sun direction, and that this limitation generally has a greater impact on smaller-sized objects. The lunar position also has a significant effect on the discoveries, with the restriction on the nights before and after the full Moon resulting in 29% of NEAs being undiscovered, and analysis shows that objects found in the first half of the lunar calendar month are generally more difficult to be followed than those found in the second half. The galactic plane, especially the direction near the galactic center, also has an effect on the discoveries, resulting in a season-dependent “blind spot” for observations near the ecliptic.

Ultracool dwarfs in Gaia DR3

Context. Previous Gaia data releases offered the opportunity to uncover ultracool dwarfs (UCDs) through astrometric, rather than purely photometric, selection. The most recent, the third data release (DR3), offers in addition the opportunity to use low-resolution spectra to refine and widen the selection. Aims. In this work we use the Gaia DR3 set of UCD candidates and complement the Gaia spectrophotometry with additional photometry in order to characterise the global properties of the set. This includes the inference of the distances, their locus in the Gaia colour-absolute magnitude diagram, and the (biased through selection) luminosity function at the faint end of the main sequence. We study the overall changes in the Gaia RP spectra as a function of spectral type. We study the UCDs in binary systems, we attempt to identify low-mass members of nearby young associations, star-forming regions, and clusters, and we analyse their variability properties. Methods. We used a forward model and the Bayesian inference framework to produce posterior probabilities for the distribution parameters and a calibration of the colour index as a function of the absolute magnitude in the form of a Gaussian process. Additionally, we applied the hierarchical mode association clustering (HMAC) unsupervised classification algorithm for the detection and characterisation of overdensities in the space of celestial coordinates, projected velocities, and parallaxes. Results. We detect 57 young, kinematically homogeneous groups, some of which are identified as well-known star-forming regions, associations, and clusters of different ages. We find that the primary members of the 880 binary systems with a UCD belong to the thin and thick disc components of the Milky Way. We identify 1109 variable UCDs using the variability tables in the Gaia archive, 728 of which belong to the star-forming regions defined by HMAC. We define two groups of variable UCDs with extreme bright or faint outliers. Conclusions. The set of sources identified as UCDs in the Gaia archive contains a wealth of information that will require focused follow-up studies and observations. It will help advance our understanding of the nature of the faint end of the main sequence and the stellar-substellar transition.

Automatic Observation of Astronomical Coordinates Using the Shandong University of Science and Technology/National Astronomical Observatories Digital Zenith Tube

Abstract The digital zenith tube (DZT) is developed based on the astrogeodetic and photogrammetric theory. One prototype of DZT integrating techniques of global positioning system (GPS) and charge-coupled device (CCD) photogrammetry has been developed jointly by Shandong University of Science and Technology and National Astronomical Observatories of Chinese Science Academy, China. It can automatically estimate astronomical coordinates in real time by CCD star image processing and GPS data processing. The DZT’s errors are analyzed in three aspects, namely, the instrument error, observation error, and data processing error. Reliability and accuracy of DZT integrating GPS and CCD are verified by the practical field operations. Observing results on many unknown points by the repeated observations of each point show the internal precision of the astronomical latitude and longitude. Observing results on several known points and the comparison with the EGM2008-derived results verify the external accuracy of the DZT, and the differences of these points in astronomical latitude and longitude are within ±0.15″ and greater than 1″, respectively.

ANALYSIS OF SPHERICAL ASTRONOMY ALGORITHMS FOR PREDICTING THE SOLAR ECLIPSE BY W.M. SMART

A solar eclipse is an unusual natural occurrence. Muslims used the phenomenon of a solar eclipse as the season for prayer, which was only carried out during a solar eclipse from early in the phenomenon until the end. Although there is no statistically significant difference in estimating a solar eclipse, as the seasons change, a solar eclipse becomes increasingly important. Lots of alternatives can be used as a reference in the determination of a solar eclipse. Among the alternatives commonly used is the calculation of spherical astronomy. Despite its complexity, many people still use it as the foundation for calculations based on solar eclipse Pythagoras as well as the determination of the celestial coordinate system.

Optical features of rotating black hole with nonlinear electrodynamics

In this article, we considered the strong field approximation of nonlinear electrodynamics black hole and constructed its rotating counterpart by applying the modified Newman–Janis algorithm. The corresponding metric function in the strong field limit of the static black hole is identified in order to study the radius of photon sphere. However, the metric function for the rotating counterpart in the strong field limit is considered in order to study the horizon radius w.r.t spin parameter. We considered the Hamilton–Jacobi method to derive the geodesic equations for photon and constructed an orthonormal tetrad for deriving the equations for celestial coordinates in the observer’s sky. Shadows, distortions and energy emission rates are investigated and the results are compared for different values of nonlinear electrodynamics parameter, charge and spin. It is found that the presence of the nonlinear electrodynamics parameter affects the shape and size of the shadows and thus the distortion in the case of rotation. It is also found that the nonlinearity of electrodynamics diminishes the flatness in the shadow due to the effect of spin and other parameters.

The angular scale of homogeneity with SDSS-IV DR16 luminous red galaxies

We report measurements of the angular scale of cosmic homogeneity (θH ) using the recently released luminous red galaxy sample of the sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV LRG DR16). It consists of a model-independent method, as we only use the celestial coordinates of these objects to carry out such an analysis. The observational data is divided into thin redshift bins, namely 0.67 < z < 0.68, 0.70 < z < 0.71, and 0.73 < z < 0.74, in order to avoid projection biases, and we estimate our uncertainties through a bootstrap method and a suite of mock catalogues. We find that the LRGs exhibit an angular scale of homogeneity consistent with the predictions of the standard cosmology within the redshift interval studied. Considering the bootstrap method, in which the measurements are obtained in a model-independent way, we found at 1σ level that θH boot(0.675) = 7.57 ± 2.91 deg, θH boot (0.705) = 7.49 ± 2.63 deg and θH boot (0.735) = 8.88 ± 2.81 deg. Such results are in good agreement with the ones obtained using mock catalogues built under the assumption of the standard cosmological model.

Effect of peak sun hour on energy productivity of solar photovoltaic power system

A solar cell is a type of renewable energy engineering technology that can convert photons coming from the sun to be converted into electrical energy. The amount of energy that can be converted by a solar cell is determined by the effective insolation time. Peak sun hours (PSH) are the focus of this research. This PSH analysis aims to determine the potential for solar energy obtained in geographical locations throughout the year. Geographical location and the position of the astronomical coordinates of a certain area affect PSH. Therefore, the orientation of solar panel installation, including the height, slope, and latitude of the solar panel surface needs to be considered in order to get maximum solar energy. The results of this study can be used by technicians in determining the orientation of solar panel development in an area.

Effect of Galactic aberration on Earth orientation parameters: From the ICRF2 to the ICRF3

Aims. At the beginning of 2019 the third realization of the International Celestial Reference Frame (ICRF3) replaced the previous version (ICRF2). In the current International Celestial Reference Frame (ICRF), a major improvement is the inclusion of the Galactic aberration (GA) effect. The Earth orientation parameters (EOP), which link the celestial and terrestrial reference frames, are thus accordingly affected. This paper investigates the influence of the ICRF evolution and the modeling of the GA effect on the determination of the EOP. Methods. The EOP time series derived within the frame of two official ICRF realizations, as well as different ways of handling the GA effect, were estimated based on the very long baseline interferometry (VLBI) observational data obtained over the past 40 yr. The correlation between the station network and the GA contribution to the EOP was then analyzed by comparison of IVS R1 and R4 routine observations, which have a different distribution of antennas. We also studied the effect of GA on nutation and free core nutation amplitudes by least-squares fits. Results. The application of different reference frames (ICRF2 and ICRF3) in VLBI solutions leads to constant offsets of 315 microarcsec in the components of dX, dY, and dUT 1. This difference is mainly the reflection of the orientation offsets between the two realizations of the International Celestial Reference System. In a separate study of the GA effect, an approximate 0.3 ± 0.3 uas yr−1 bias is found in dY, while other components are not significantly affected. This bias results in an increasing offset in precession which is non-negligible after several tens of years. We further found that the bias caused by the GA effect will decrease when using a set of more uniformly distributed sources or stations in the most recent decades.

Elements of celestial conformal field theory

In celestial holography, four-dimensional scattering amplitudes are considered as two-dimensional conformal correlators of a putative two-dimensional celestial conformal field theory (CCFT). The simplest way of converting momentum space amplitudes into CCFT correlators is by taking their Mellin transforms with respect to light-cone energies. For massless particles, like gluons, however, such a construction leads to three-point and four-point correlators that vanish everywhere except for a measure zero hypersurface of celestial coordinates. This is due to the four-dimensional momentum conservation law that constrains the insertion points of the operators associated with massless particles. These correlators are reminiscent of Coulomb gas correlators that, in the absence of background charges, vanish due to charge conservation. We supply the background momentum by coupling Yang-Mills theory to a background dilaton field, with the (complex) dilaton source localized on the celestial sphere. This picture emerges from the physical interpretation of the solutions of the system of differential equations discovered by Banerjee and Ghosh. We show that the solutions can be written as Mellin transforms of the amplitudes evaluated in such a dilaton background. The resultant three-gluon and four-gluon amplitudes are single-valued functions of celestial coordinates enjoying crossing symmetry and all other properties expected from standard CFT correlators. We use them to extract OPEs and compare them with the OPEs extracted from multi-gluon celestial amplitudes without a dilaton background. We perform the conformal block decomposition of the four-gluon single-valued correlator and determine the dimensions, spin and group representations of the entire primary field spectrum of the Yang-Mills sector of CCFT.

The proper motion of stars in dwarf galaxies: distinguishing central density cusps from cores

ABSTRACT We show that measuring the proper motion of ∼2000 stars within a dwarf galaxy, with an uncertainty of 1 km s−1 at most, can establish whether the dark matter (DM) density profile of the dwarf has a central core or cusp. We derive these limits by building mock star catalogues similar to those expected from future astrometric Theia-like missions and including celestial coordinates, radial velocity and proper motion of the stars. The density field of the DM halo of the dwarf is sampled from an extended Navarro–Frank–White (eNFW ) spherical model, whereas the number density distribution of the stars is a Plummer sphere. The velocity field of the stars is set according to the Jeans equations. A Monte Carlo Markov chain algorithm applied to a sample of N ≳ 2000 stars returns unbiased estimates of the eNFW DM parameters within $10{{\ \rm per\, cent}}$ of the true values and with 1σ relative uncertainties ≲ 20 per cent. The proper motions of the stars lift the degeneracy among the eNFW parameters which appears when the line-of-sight velocities alone are available. Our analysis demonstrates that, by estimating the log-slope of the mass density profile estimated at the half-light radius, a sample of N = 2000 stars can distinguish between a core and a cusp at more than 8σ. Proper motions also return unbiased estimates of the dwarf mass profile with 1σ uncertainties that decrease, on average, from 2.65 dex to 0.15 dex when the size of the star sample increases from N = 100 to N = 6000 stars. The measure of the proper motions can thus strongly constrain the distribution of DM in nearby dwarfs and provides fundamental contribution to understanding the nature and the properties of DM.

Higher-dimensional charged black holes in f(R)-gravity's rainbow surrounded by cloud of strings: Exact solution, shadow, and effective potential barrier

We construct a new class of spherically symmetric black hole solutions in f(R)-gravity's rainbow1 framework which is surrounded by string cloud configuration. In the thermodynamic analysis, we show that the black hole's temperature grows up for such small values of b parameter and also big values of it, graphically. In addition to the mass and charge of the black holes, we show that the presence of the rainbow function gr(ε) and cloud's strength b can also affect the size of the shadow. For the black hole solution, it is shown that the shadow size increases with the parameter b, but decreases with the parameter gr(ε). In addition, we have shown that the energy emission rate decreases with increase in gr(ε) and decrease in b parameter. We have analyzed the concept of effective potential barrier by transforming the radial equation of motion into standard Schrodinger form. The most important result derived from this study is that the height of this potential increases with decrease in gr(ε) parameter and increases in the coupling constant λ and the b parameter. We also investigate the impact of these parameters on the other thermodynamical quantities like temperature and heat capacity. There is a minimum on that between for one special value of b. From the temperature diagram versus the b parameter (T−b) and analogy with T−r+ diagrams, we can say that the b parameter behaves as the event horizon radius r+. Regarding the cosmological constant as a thermodynamic pressure and its conjugate quantity as a thermodynamic volume, we investigate the critical behavior of our black hole solutions. In d=5, the P-V diagrams are more complex than that of the standard Van der Waals. These diagrams behave like the Born–Infeld-AdS P-V diagrams. When d=6, the P-V diagrams are also more complex than that of the standard Van der Waals and we decompose them into two parts. One part behaves like the standard Van der Waals system. The other part is similar to the Schwarzschild-AdS black hole P-V diagrams where the isotherms turn and enter a region with negative pressures. The null geodesic equations are computed in d=5 spacetime dimensions by using the concept of symmetries and Hamilton-Jacobi equation and Carter separable method. With the null geodesics in hand, we then evaluate the celestial coordinates (x, y) and the radius Rs of the black hole shadow and represent it graphically.

Grid, Geodetic and Astronomical Azimuth Conversions in Ghana

Astronomic azimuths had been used for orienting old surveys in Ghana. With technological advancement and the development of simpler but accurate equipment and techniques for measurement, this has been replaced by the use of the Global Navigational Satellite System (GNSS) techniques such as the Global Positioning System(GPS). However, the use of these for azimuth determinations results in a different type of azimuth as opposed to astronomic azimuths previously used. For retracing some of those old surveys based on Astronomical coordinates, the relationship and convertibility between the different azimuths is imperative. In this exploration, the relationship and precision of both techniques were tested on various baselines located in different parts of the country. This involved the computation of Astronomic, Geodetic and Grid Azimuths between pairs of points to form several baselines. These baselines span from the Southern to the Middle belt portions of the Country where triangulations have been done, as some of these triangulation stations were Laplace stations that have both astronomic and geodetic coordinates determined for them. The results were investigated in terms of effect of using the convergence and t-T correction to convert between the set of azimuths. The results show that Geodetic Azimuths could be converted to grid coordinates and vice versa to accuracies of mean 0° 0ʹ 0.56ʺ and standard deviation ± 5.6 seconds. However, for Astronomic to Grid Azimuths, without correcting for Deflection of vertical, the conversion is accurate only to mean differences of 0° 1ʹ 25.3ʺ with standard deviation ± 0° 8ʹ 21.5ʺ. The results show the necessity of the Laplace correction for vertical deflection in astronomic azimuths in addition to the convergence and t-T correction and recommends the provision of country-wide deflection corrections.

Geodesics and shadow formed by a rotating Gauss–Bonnet black hole in AdS spacetime

The latest findings of static and spherically symmetric black hole solution give a potential platform to investigate the novel four-dimensional Einstein Gauss–Bonnet gravity. In order to obtain a rotating black hole solution, we first adopt the Newman Janis algorithm and study the structure of its horizons. To analyze the said black hole shadow, we move forward to compute expressions of the celestial coordinates using the geodesic equations. Furthermore, we provide a detailed analysis of the shadow size and its distortion parameter, adopting the Hioki and Maeda method, together with the applications of a supermassive black hole shadow in the center of nearby galaxy Messier 87 and obtained constraints on the relationships of spin and charge. From the obtained results, we demonstrate that both spin and coupling parameters of the black hole have a substantial influence on shadow structure. The increment in the values of these parameters diminishes the shadow radius. We also study the energy emission rate using the Hawking temperature. Furthermore, it is shown that whenever the collision of two electrically neutral test particles takes place in the vicinity of the black hole horizon, the Gauss–Bonnet black hole may serve as a particle accelerator with an infinitely large center of mass energy.

An analysis of Ibn al-Shāṭir’s star table

Ibn al-Shāṭir’s (1306–1375/1376 AD) star table in his Jadīd zīj, comprising of the equatorial coordinates and magnitudes of 89 stars, is edited and analyzed in this paper on the basis of the extant manuscripts going back to the late 14th and early 15th centuries. It established a new tradition of arranging the celestial coordinates in the star tables in Egypt and Syria after him. The right ascensions (mean absolute error MAE = 20.0′, mean error μ = –2.8′, standard deviation σ = 29.1′) and the declinations ( MAE = 21.1′, μ = –3.2′, σ = 29.3′) are nearly of the same degree of precision. The stars in the region RA ~ 120°–180° generally have the least errors in both declination and right ascension. The declinations of the southern stars were measured more precisely than those of the northern ones. The values for the declinations of the stars in the region δ ~ –30°–0° (the middle of the sky towards the south of the horizon of Damascus) are significantly the most accurate. A systematic northward shift can be seen in the declinations of the southern stars. The declinations of 15 of 18 stars spreading out in RA ~ 67°–121° show a southerly, downward shift. More than 65% of the stars have the errors in both the declination and right ascension less than 32′. No outlier in the tabular coordinates exceeds ±98′. Also, Ibn al-Shāṭir measured the magnitudes of, at least, a few stars: he assigned a correct magnitude of +4 to λ Ori, a component of the star cluster in the Orion that was considered a nebulous object in the Almagest star catalogue, and presented more precise values for the magnitudes of α Sco, α Oph, β Cas, κ Ori, γ Gem, and β CMi than Ptolemy and al-Ṣūfi.

Rotating charged black hole shadow in quintessence

We analytically study the shadow of the charged rotating black hole in the presence of quintessence. The quintessential energy adequately affects the shape and size of the black hole shadow. The shadow of a rotating black hole spots a distorted dark disk. The shape and size of the black hole shadow depend on its mass M, spin parameter a, charge q, quintessential field parameter ωq, and normalization factor c. We derive the entire geodesic structure of photons near black holes using the Hamilton–Jacobi equation and Carter constant separable method. We relate the celestial coordinates to geodesic equations and plot the contour of the black hole shadow for the case ωq=−2/3. To find the effect of quintessential energy on the black hole shadow, we obtain observable i.e. shadow radius Rs and distortion parameter δs. We compare all our results with the Kerr black hole in quintessence, Kerr–Newman black hole and Bardeen–Kiselev black hole. Our study shows that for a fixed value of the spin parameter a and normalization factor c, the black hole shadow monotonically decreases and gets more distorted with charge q.

Study of circular geodesics and shadow of rotating charged black hole surrounded by perfect fluid dark matter immersed in plasma

In this work, we consider a rotating charged black hole surrounded by perfect fluid dark matter. We consider the system to be immersed in non-magnetised, pressureless plasma. First, we evaluate the null geodesics in order to study the co-rotating and counter rotating photon orbits. Further, we analyse the null geodesics to calculate the celestial coordinates (α, β). The celestial coordinates are used to determine the black hole shadow radius (R s). Thereafter, we observe and analyse the effects of black hole spacetime, perfect fluid dark matter and plasma parameters (a, Q, χ, k) on the black hole shadow in detail. Finally, we study the effect of plasma distribution on the effective potential (V eff) of the black hole spacetime as encountered by the photons. We also present bounds on the plasma parameter from the observational data from M87* central supermassive black hole.

Astrometric Calibration for All-sky Camera with Machine Learning

The night images obtained with an all-sky camera can provide spatial and time sampling, which can be used for measurement cloud coverage measurement and meteor monitoring. The astrometric calibration of an all-sky camera is necessary because of strong field distortions. We use machine learning to complete the calibration of an all-sky camera. In order to prepare the data sets needed for machine learning, a particle swarm optimization algorithm is used to determine the parameters of the method proposed by Borovicka in 1995. Machine learning can transform plate coordinates to celestial coordinates and transform celestial coordinates to plate coordinates. The actual test shows that the standard deviation of residuals is of the order of 1′ for the transformation from plate coordinates to celestial coordinates and the standard deviation of residuals is of the order of 0.3 px for the transformation from celestial coordinates to the plate coordinates.

Evaluation of the ICRF stability from a position time series analysis

Context. The celestial reference frame is established on the basis of the absolute positions of extragalactic sources that are assumed to be fixed in space. The fixing of the axes is one of the crucial points for the concept behind the International Celestial Reference System (ICRS). However, due to various effects such as its intrinsic activity, the apparent position of the extragalactic sources may vary with time, resulting in a time-dependent deviation of the frame axes that are defined by the positions of these sources. Aims. We aim to evaluate the axis stability of the third realization of the International Celestial Reference Frame (ICRF3). Methods. We first derived the extragalactic source position time series from observations of very long baseline interferometry (VLBI) at the dual S∕X-band (2.3/8.4 GHz) between August 1979 and December 2020. We measured the stability of the ICRF3 axes in terms of the drift and scatter around the mean: (i) we estimated the global spin of the ICRF3 axes based on the apparent proper motion (slope of the position time series) of the defining sources of the ICRF3; (ii) we also constructed the yearly representations of the ICRF3 through annually averaged positions of the defining sources of the ICRF3 and estimated the dispersion in the axes orientation of these yearly frames. Results. The global spin is no higher than 0.8 μas yr-1 for each ICRF3 axis with an uncertainty of 0.3 μas yr-1, corresponding to an accumulated deformation smaller than 30 μas for the celestial frame axes during 1979.6–2021.0. The axes orientation of the yearly celestial frame becomes more stable as time elapses, with a standard deviation of 10 μas–20 μas for each axis. Conclusions. The axes of the ICRF3 are stable at approximately 10 μas–20 μas from 1979.6–2021.0 and the axes stability does not degrade after the adoption of the ICRF3.

Influence of accretion flow and magnetic charge on the observed shadows and rings of the Hayward black hole

The feature of the observed shadows and rings of an astrophysical black hole (BH) may depend on its accretion flows and magnetic charge. We find that the shadow radii and critical impact parameters of the Hayward BH are decreased with the increase of the magnetic charge. Comparing the Schwarzschild BH with the Hayward BH using the ray-tracing method, we show that the density and deflection of lights increase with the magnetic charge, and the BH singularity does not affect the generation of the shadow. Based on three optically thin accretion flow models, the two-dimensional shadows in celestial coordinates are derived. It is found that the shadow and photon ring luminosities of a Hayward BH surrounded by infalling spherical accretion flow are dimmer than that of a static spherical accretion flow. Taking three kinds of inner radii at which the accretion flow stops radiating, we find that the observed luminosity of a Hayward BH surrounded by a thin disk accretion flow is dominated by the direct emission, and the photon ring emission has a weak influence on it. These results suggest that the size of the observed shadow is related to the space-time geometry, and the luminosities of both the shadows and rings are affected by the accretion flow property and the BH magnetic charge.

Ambidextrous light transforms for celestial amplitudes

Low multiplicity celestial amplitudes of gluons and gravitons tend to be distributional in the celestial coordinates z, overline{z} . We provide a new systematic remedy to this situation by studying celestial amplitudes in a basis of light transformed boost eigenstates. Motivated by a novel equivalence between light transforms and Witten’s half-Fourier transforms to twistor space, we light transform every positive helicity state in the coordinate z and every negative helicity state in overline{z} . With examples, we show that this “ambidextrous” prescription beautifully recasts two- and three-point celestial amplitudes in terms of standard conformally covariant structures. These are used to extract examples of celestial OPE for light transformed operators. We also study such amplitudes at higher multiplicity by constructing the Grassmannian representation of tree-level gluon celestial amplitudes as well as their light transforms. The formulae for n-point Nk−2MHV amplitudes take the form of Euler-type integrals over regions in Gr(k, n) cut out by positive energy constraints.