Celestial Positions Research Articles

PSR J0210+5845: Ultra-wide binary pulsar with a B6 V main sequence star companion

We report on radio timing observations of PSR J0210+5845 that reveal large deviations from typical pulsar spin-down behaviour. We interpret these deviations as being due to the binary motion around the V = 13.5 star 2MASS J02105640+5845176, which is coincident in terms of its celestial position and distance with the pulsar. Archival observations and new optical spectroscopy have identified this object as a B6 V star, with a temperature of Teff ≈ 14 000 K and a mass of Mc = 3.5 to 3.8 M⊙, making it the lowest mass for a main sequence star known to be orbiting a non-recycled pulsar. We find that the timing observations constrain the binary orbit to be wide and moderately eccentric, with an orbital period of Pb = 47−14+40 yr and eccentricity of e = 0.46−0.07+0.10. We predict that the next periastron passage will occur between 2030 and 2034. Due to the low companion mass, we find that the probability for a system with the properties of PSR J0210+5845 and its binary companion to survive the supernova is low. We show that a low velocity and fortuitously directed natal kick is required for the binary to remain bound during the supernova explosion and we argue that an electron-capture supernova is a plausible formation scenario for the pulsar.

A new method for high-precision starlight refraction indirect horizon-sensing positioning of atmospheric flight vehicles

The starlight refraction indirect horizon-sensing positioning method is a new type of autonomous celestial navigation method with broad application prospects. In view of this method currently being limited to the spacecraft outside the atmosphere, this article derives and establishes a starlight refraction indirect horizon-sensing positioning model between the starlight refraction angle and the flight vehicle’s position inside the atmosphere. Based on this model, a new starlight refraction indirect horizon-sensing positioning method for the flight vehicle inside the atmosphere is proposed. According to the atmospheric refraction law and the spherical atmospheric model, the refracted optical path of starlight entering the atmosphere and reaching the flight vehicle is traced, so as to establish a starlight refraction positioning model that reflects the relationship between the refraction angle and the 3-D position of the flight vehicle inside the atmosphere. Subsequently, by employing star sensors on the flight vehicle to measure the starlight refraction angle, and combining the starlight refraction positioning model that maps the starlight refraction angle and the flight vehicle’s position, a starlight refraction indirect horizon-sensing autonomous celestial positioning method, tailored for the flight within the atmosphere, is proposed. Finally, the effectiveness of the proposed method is verified through ground semi physical experiments, and an analysis is conducted to explore the factors that affect the positioning accuracy of the starlight refraction indirect horizon-sensing positioning method within the atmosphere.

Likelihood of the sky

Catalogs with celestial positions and uncertainties are among the primary data products of observational astronomy. Consequently, the (cross-)matching problem, namely, the question of how many (and which) pairs of positions pertain to the same celestial source, remains a central part of this scientific exploitation. We address the matching problem for two catalogs from a purely geometric point of view by adopting the concept of point processes and nearest-neighbor distributions. Suitable expressions for the nearest-neighbor distributions were derived and used to model the distribution of spatial offsets in the sky. Thus, we are able to estimate a total number of matching pairs, along with individual matching probabilities between sources in any two catalogs of positions and uncertainties. We demonstrate the workings of the model using mock data and apply it to cross-matching the X-ray sources of the eROSITA Final Equatorial-Depth survey with opticalGaiacounterparts.

Gaia Data Release 3: Summary of the content and survey properties

We present the third data release of the European Space Agency's Gaia mission, GDR3. The GDR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. The GDR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photometry in the G, G$_{BP}$, and G$_{RP}$ pass-bands already present in the Early Third Data Release. GDR3 introduces an impressive wealth of new data products. More than 33 million objects in the ranges $G_{rvs} < 14$ and $3100 <T_{eff} <14500 $, have new determinations of their mean radial velocities based on data collected by Gaia. We provide G$_{rvs}$ magnitudes for most sources with radial velocities, and a line broadening parameter is listed for a subset of these. Mean Gaia spectra are made available to the community. The GDR3 catalogue includes about 1 million mean spectra from the radial velocity spectrometer, and about 220 million low-resolution blue and red prism photometer BPRP mean spectra. The results of the analysis of epoch photometry are provided for some 10 million sources across 24 variability types. GDR3 includes astrophysical parameters and source class probabilities for about 470 million and 1500 million sources, respectively, including stars, galaxies, and quasars. Orbital elements and trend parameters are provided for some $800\,000$ astrometric, spectroscopic and eclipsing binaries. More than $150\,000$ Solar System objects, including new discoveries, with preliminary orbital solutions and individual epoch observations are part of this release. Reflectance spectra derived from the epoch BPRP spectral data are published for about 60\,000 asteroids. Finally, an additional data set is provided, namely the Gaia Andromeda Photometric Survey (abridged)

Research on joint calibration and compensation of the inclinometer installation and instrument errors in the celestial positioning system

AbstractThe application of celestial navigation based on inclinometer to aircraft in near‐earth space and planetary rovers is a significant development direction. Due to the installation and instrument errors of the inclinometer, it is difficult for tilted platforms to obtain high‐precision positioning results. But the installation error of the inclinometer is coupled with the error of the instrument itself, and there is no effective way to measure the two errors separately. To improve the positioning accuracy of the tilted platform, a joint calibration and compensation algorithm of the inclinometer's installation and instrument errors is proposed. First, based on the principle of celestial positioning, the influence analysis model of the inclinometer error on the positioning accuracy is built according to the definition of inclinometer installation error and instrument error, which indicates the traditional algorithms are not suitable for tilted platforms. Then, a joint calibration and compensation algorithm for the inclinometer installation and instrument errors is presented based on coordinate transformation relationship and error propagation characteristics. Finally, a ground test platform is built and the experimental verification of the joint calibration and compensation algorithm of inclinometer error is accomplished. Experiment results show the root mean square errors of the longitude and latitude are and , and the mean distance error is 397.46 m, which is far less than the mean distance error 3629.27 m of the traditional calibration algorithm. It indicates the joint calibration and compensation algorithm can effectively compensate for the errors caused by the inclinometer and obtain higher positioning accuracy.

A Novel Analytical Solution Method for Celestial Positioning

Traditional celestial navigation adopts the intercept method or Sumner line method in order to solve the fix problems of celestial sight reduction. While an estimated position is often needed in order to complete celestial positioning, these methods are not rigorous and they have many shortcomings. Thus, this study has analyzed the geometry of the circle of equal altitude and the two-body problem. Furthermore, vector methods are proposed without using spherical trigonometry, in order to meet navigation needs. Finally, web mapping was used to display the results. The results show that the two methods that are proposed in this study had better accuracy, practical convenience, and faster computing speed than those which have been proposed by other studies. The two methods’ capability to avoid complicated manual calculations and chart work processes makes them highly suitable as an alternative to the use of global navigation satellite systems. These methods enable maritime school students to quickly understand the principles of celestial navigation through computing and graphical interfaces.

Testiranje funkcionalnosti i primjenjivosti pametnih uređaja za ručni sustav astronomske navigacije

In this paper, the functionality and applicability of smart devices for the purpose of handheld celestial navigation systems is investigated. The main instrument used to determine observer position (altitude measurements) in celestial navigation is the sextant. The use of a sextant and almanac or computer is a classical approach to determining the observer's celestial position. This approach has two significant limitations, firstly the time window for the measurements is short, and secondly, the view of the ocean horizon must be clear. With the use of smart devices, we can overcome these two obstacles and create a so-called handheld celestial navigation system. Currently, smart devices have very accurate sensors to measure various physical quantities such as acceleration, angular velocity, orientation, etc. We are particularly interested in validating the orientation sensor for measuring the altitude and azimuth of the celestial body. The altitude of the celestial body is the primary parameter in determining the celestial position using a sextant. The idea is to replace the sextant with a smart device to measure the altitude and possibly the azimuth of the celestial body. To test this idea, two types of experiments are designed. In the first, a system on a tripod to obtain the most accurate measurements possible is set. Such tests will provide detailed information about the accuracy of the smart device's sensors and its applicability in measuring altitude and azimuth. The test system will essentially resemble a theodolite device. In the second experiment, a hands-free measurement experiment that resembles a sextant to test the idea for practical use and functionality in the process of celestial positioning is set. The observed data show that the results of the measurements under controlled conditions are promising and within reasonable bounds for the accuracy of celestial positioning. Estimates of the position error by the graphical method are in the range of 10 Nm to 30 Nm. In order to obtain a fully functional stand-alone celestial positioning system, the proposed assembly needs to be improved through several unchallenging upgrades. A fully functional system can be considered as a cheap off-the-shelf handheld Celestial Navigational System (CNS).

Adaptive celestial positioning for the stationary Mars rover based on a self-calibration model for the star sensor

AbstractThis paper proposes a method for self-calibrating the star sensor on the Mars rover considering several years of exploration on the surface of Mars. The natural stars in the night sky are considered the control points, and a self-calibration model is deduced in detail according to an imaging model. An adaptive celestial positioning (ACP) algorithm is then introduced, and the calculation procedure is presented in detail to realise self-adjustment based on the self-calibration of the star sensor. Three field tests were conducted on Earth, the results of which show good self-calibration and celestial positioning performances. The positioning results indicate an obvious accuracy improvement using the ACP algorithm compared with that without calibration. Multiple positionings in one night can improve the celestial positioning accuracy to approximately 15 m. For future studies, this self-calibration model will be useful not only for star sensors but also for other optical sensors, such as sun sensors and binocular or stereo-vision cameras.

Guidance navigation and control technology for the lunar ascent vehicle of the Chang&amp;rsquo;e-5 mission

<p indent="0mm">The limitations of the remote control network and the lunar launch platform mean that many technologies differing from those of carrier rockets of the earth are required to transport samples from the hostile lunar environment. The Chang’e-5 mission uses some new techniques, such as the autonomous celestial positioning and orientating method, gravity measurement, and the adaptive powered explicit guidance algorithm, to improve the precision of entry into orbit. Furthermore, other techniques, including the fault diagnosis algorithm with threshold dynamic adjustment, thrust detection and reconstruction, non-interactive emergency guidance for ascent, and an autonomous orbit control strategy for salvage, are adopted to improve the safety of ascent from the lunar surface. These techniques enabled China to complete the moon launch successfully in the historic Lunar Sample Return mission.

The CHIME Pulsar Project: System Overview

We present the design, implementation and performance of a digital backend constructed for the Canadian Hydrogen Intensity Mapping Experiment (CHIME) that uses accelerated computing to observe radio pulsars and transient radio sources. When operating, the CHIME correlator outputs 10 independent streams of beamformed data for the CHIME/Pulsar backend that digitally track specified celestial positions. Each of these independent streams are processed by the CHIME/Pulsar backend system which can coherently dedisperse, in real-time, up to dispersion measure values of 2500 pc/cm$^{-3}$ . The tracking beams and real-time analysis system are autonomously controlled by a priority-based algorithm that schedules both known sources and positions of interest for observation with observing cadences as small as one day. Given the distribution of known pulsars and radio-transient sources, the CHIME/Pulsar system can monitor up to 900 positions once per sidereal day and observe all sources with declinations greater than $-20^\circ$ once every $\sim$2 weeks. We also discuss the science program enabled through the current modes of data acquisition for CHIME/Pulsar that centers on timing and searching experiments.

Gaia Early Data Release 3

We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (G_BP-G_RP) colour are also available. The passbands for G, G_BP, and G_RP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 percent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30--40 percent for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, G_BP, and G_RP is valid over the entire magnitude and colour range, with no systematics above the 1 percent level.

Functional Principal Component Analysis of Radio–Optical Reference Frame Tie

Abstract The Gaia optical reference frame is intrinsically undefined with respect to global orientation and spin, so it needs to be anchored in the radio-based International Celestial Reference Frame (ICRF) to provide a referenced and quasi-inertial celestial coordinate system. The link between the two fundamental frames is realized through two samples of distant extragalactic sources, mostly active galactic nuclei and quasars, but only the smaller sample of radio-loud ICRF sources with optical counterparts is available to determine the mutual orientation. The robustness of this link can be mathematically formulated in the framework of functional principal component analysis using a set of vector spherical harmonics to represent the differences in celestial positions of the common objects. The weakest eigenvectors are computed, which describe the greatest deficiency of the link. The deficient or poorly determined terms are specific vector fields on the sphere that carry the largest errors of absolute astrometry using Gaia in reference to the ICRF. This analysis provides guidelines for the future development of the ICRF maximizing the accuracy of the link over the entire celestial sphere. A measure of the robustness of a least-squares solution, which can be applied to any linear model fitting problem, is introduced to help discriminate between reference frame tie models of different degrees.

The star catalogue of Wilhelm IV, Landgraf von Hessen-Kassel

We analyse a manuscript star catalogue by Wilhem IV, Landgraf von Hessen-Kassel from 1586. From measurements of altitudes and of angles between stars, given in the catalogue, we find that the measurement accuracy averages 26″ for eight fundamental stars, compared to 49″ of the measurements by Brahe. The computation in converting altitudes to declinations and angles between stars to celestial positions is very accurate, with errors that are negligible with respect to the measurement errors. Due to an offset in the position of the vernal equinox, the positional error of the catalogue is slightly worse than that of Brahe’s catalogue; however, when a correction is made for the offset, which was known to 17th century astronomers, the catalogue is more accurate than that of Brahe by a factor of two. We provide machine-readable tables of the catalogue.

GaiaEarly Data Release 3

Context.We present the early installment of the thirdGaiadata release,GaiaEDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities fromGaiaDR2.Aims.A summary of the contents ofGaiaEDR3 is presented, accompanied by a discussion on the differences with respect toGaiaDR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use ofGaiaEDR3 results.Methods.The raw data collected with theGaiainstruments during the first 34 months of the mission have been processed by theGaiaData Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect toGaiaDR2 in terms of astrometric and photometric precision, accuracy, and homogeneity.Results. GaiaEDR3 contains celestial positions and the apparent brightness inGfor approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (GBP−GRP) colour are also available. The passbands forG,GBP, andGRPare provided as part of the release. For ease of use, the 7 million radial velocities fromGaiaDR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part ofGaiaDR3. Finally,GaiaEDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, theGaia-CRF3, which is based solely on extragalactic sources. The creation of the source list forGaiaEDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that forGaiaDR2, but it does feature new sources and there are some notable changes. The source list will not change forGaiaDR3.Conclusions. GaiaEDR3 represents a significant advance overGaiaDR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30–40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband forG,GBP, andGRPis valid over the entire magnitude and colour range, with no systematics above the 1% level

Late 19th century navigational uncertainties and their influence on sea surface temperature estimates

Accurate estimates of historical changes in sea surface temperatures (SSTs) and their uncertainties are important for documenting and understanding historical changes in climate. A source of uncertainty that has not previously been quantified in historical SST estimates stems from position errors. A Bayesian inference framework is proposed for quantifying errors in reported positions and their implications on SST estimates. The analysis framework is applied to data from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS3.0) in 1885, a time when astronomical and chronometer estimation of position was common but predated the use of radio signals. Focus is upon a subset of 943 ship tracks from ICOADS3.0 that report their position every two hours to a precision of 0.01∘ longitude and latitude. These data are interpreted as positions determined by dead reckoning that are periodically updated by celestial correction techniques. The posterior medians of uncertainties in celestial correction are 33.1 km (0.30∘ on the equator) in longitude and 24.4 km (0.22∘) in latitude, respectively. Celestial navigation uncertainties being smaller in latitude than longitude is qualitatively consistent with the relative difficulty of obtaining astronomical estimates. The posterior medians for two-hourly dead reckoning uncertainties are 19.2% for ship speed and 13.2∘ for ship heading, leading to random position uncertainties with median 0.18∘ (20 km on the equator) in longitude and 0.15∘ (17 km) in latitude. Reported ship tracks also contain systematic position uncertainties relating to precursor dead-reckoning positions not being updated after obtaining celestial position estimates, indicating that more accurate positions can be provided for SST observations. Finally, we translate position errors into SST uncertainties by sampling an ensemble of SSTs from the Multiscale Ultrahigh Resolution Sea Surface Temperature (MURSST) data set. Evolving technology for determining ship position, heterogeneous reporting and archiving of position information, and seasonal and spatial changes in navigational uncertainty and SST gradients together imply that accounting for positional error in SST estimates over the span of the instrumental record will require substantial additional effort.

Stereo celestial positioning of space-based double satellites to space target

Stereo celestial positioning of space-based double satellites to space target

Solar System Encounters with Open Star Clusters

The time and minimum distances of approaches were calculated more than 100 open star clusters (OSCs) near the Solar System over the past 5 Myr. It was shown that the closest proximity of the centers of the OSCs to the Solar System usually exceeded 60 pc. The Hyades cluster approached the Solar System at ~25 pc. The effect of such encounters on the comet motion in the outer regions of the Oort cloud is comparable and may even exceed the effect of encounters with individual stars. The celestial positions of the cluster antiapex were compared with the aphelia of long-period comets. Cases of its close positions were revealed for some comets and the interstellar asteroid 1I/2017 U1 (Oumuamua). The frequency of OSC passages in the vicinity of the Solar System was estimated. Encounters at a distance of 25 pc occur at a rate of ~20 times per billion years.

Influence of the Galactic Gravitational Field on the Positional Accuracy of Extragalactic Sources. II. Observational Appearances and Detectability

Abstract We consider the possibility of detecting the jitter effect of apparent celestial positions of distant sources due to local fluctuations of the Galaxy gravitational field. The observation of two samples of extragalactic sources (target and control) in different sky directions using the high-precision radio interferometry is proposed. It is shown that on a scale of ∼2 yr, it is possible to detect a systematic increase in the standard deviation of measured arc lengths of pairs of target sources compared to the control ones at the 3σ level if the accuracy of differential astrometric observations is around 10 μas. For the current state-of-the-art accuracy of 30 μas achieved at the KVN or VERA interferometers, which have shorter baselines in comparison with very long baseline interferometry, the target and control samples will differ only at the 2σ level on the scale of 10 yr. To achieve the 3σ level on this time interval, it is necessary to improve the accuracy up to ∼20 μas. Other possible effects that can also affect the arc length measurements between two sources are discussed, and an observational strategy to minimize them is suggested.

Extremely High Energy (E &gt; 1020 eV) Cosmic Rays: Potential Sources

One of the unsolved problems of cosmic ray physics is determining the nature and sources of ultrahigh energy cosmic rays (UHECRs, E > 1018 eV). The high degree of isotropy of the observed UHECR intensity caused mainly by the deviations of the UHECR trajectories in extragalactic and Galactic magnetic fields, as well as the significant uncertainty in their chemical composition (atomic mass), preclude one from tracing the observed events to their sources and finding the mechanisms for their acceleration. There are two ways to reduce the influence of magnetic deflection: by considering events with extremely high energy (EHECR, E > 1020 eV) and taking into account modern models of the Galactic magnetic field to correct its influence on the EHECR trajectory. In this study, the observed arrival directions of EHECRs from the Pierre Auger Observatory (PAO) and Telescope Array (TA) detectors' data are adjusted for the influence of Galactic and random extragalactic magnetic fields. New celestial positions of EHECRs are compared to the samples of potential sources used by the PAO—17 active galactic nuclei (AGNs) with powerful gamma radiation (from the 2FHL catalog) and 23 starburst galaxies (radio-flux-selected)—as well as with samples of 42 radio-galaxies from the parameterized catalog of radio-galaxies and magnetars. Taking into account the energy loss length of the nuclear component (H, He, C, Si, Fe) of EHECRs in the extragalactic environment and the expected typical distances to potential sources (~100 Mpc for H and Si-Fe and ~50 Mpc for He and C), the astrophysical objects that could be sources of relevant events were distinguished in the above samples. The potential acceleration mechanisms in the selected objects are analyzed, and the contribution of possible Galactic sources to the observed EHECR flux is evaluated.

Norm of the Position Shift of a Celestial Body in a Dynamical Astronomy Problem

The averaging method is widely used in celestial mechanics, in which a mean orbit is introduced and slightly deviates from an osculating one, as long as disturbing forces are small. The difference $$\delta {\mathbf{r}}$$ in the celestial body positions in the mean and osculating orbits is a quasi-periodic function of time. Estimating the norm $$\left\| {\delta {\mathbf{r}}} \right\|$$ for deviation is interesting to note. Earlier, the exact expression of the mean-square norm for one problem of celestial mechanics was obtained: a zero-mass point moves under the gravitation of a central body and a small perturbing acceleration $${\mathbf{F}}$$. The vector $${\mathbf{F}}$$ is taken to be constant in a co-moving coordinate system with axes directed along the radius vector, the transversal, and the angular momentum vector. Here, we solved a similar problem, assuming the vector $${\mathbf{F}}$$ to be constant in the reference frame with axes directed along the tangent, the principal normal, and the angular momentum vector. It turned out that $${{\left\| {\delta {\mathbf{r}}} \right\|}^{2}}$$ is proportional to $${{a}^{6}}$$, where $$a$$ is the semi-major axis. The value $${{\left\| {\delta {\mathbf{r}}} \right\|}^{2}}{{a}^{{ - 6}}}$$ is the weighted sum of the component squares of $${\mathbf{F}}$$. The quadratic form coefficients depend only on the eccentricity and are represented by the Maclaurin series in even powers of $$e$$ that converge, at least for $$e < 1$$. The series coefficients are calculated up to $${{e}^{4}}$$ inclusive, so that the correction terms are of order $${{e}^{6}}$$.