Astronomical Systems Research Articles

Observations of Near-Earth Optical Transients with the Lomonosov Space Observatory

The results of observations with the MASTER-SHOK robotic wide-field optical cameras onboard the Lomonosov Space Observatory carried out in 2016 are presented. In all, the automated transient detection system transmitted 22 181 images of moving objects with signal-to-noise ratios greater than 5 to the Earth. Approximately 84% of these images are identified with well-known artificial Earth satellites (including repeated images of the same satellite) and fragments of such satellites (space debris), according to databases of known satellites. The remaining 16% of the images are relate to uncatalogued objects. This first experience in optical space-based monitoring of near-Earth space demonstrates the high efficiency and great potential of using large-aperture cameras in space, based on the software and technology of the MASTER robotic optical complexes (the Mobile Astronomical System of TElescope-Robots (MASTER) global network of robotic telescopes of Lomonosov Moscow State University).

An efficient modeling of series‐parallel structure for the digital downconversion of pulsar signals in astronomical observation system

AbstractThis paper proposes an efficient modeling of series‐parallel structure for the digital downconversion (DDC) implemented in the field programmable gate array for astronomical observation system. The received signals by a radio telescope are of intermediate frequency, and they can be stored and analyzed only after having been converted into digital baseband signals. Although many algorithms have been proposed for the traditional DDC, it is still hard to balance the working frequency of signals and the hardware resources of field programmable gate array. The proposed series‐parallel structure can not only solve the problem but also provide a more compact size, lower consumption of power, and transplanting ability for the DDC module. The new structure has been used for the signal processing of pulsars in an astronomical observation system, and those merits have been validated.

Method of reducing photon noise and turbulence for laser guide-star detection on large-aperture telescopes

Adaptive optics systems (AOSs) rely on good estimation of a distorted wavefront. Two problems make centroid detection difficult, namely, the problem of a relatively large subaperture that brings high-order aberrations and that of a large laser guide-star spot that brings in a large photon noise. To solve these problems, we proposed an estimation method based on Poisson statistics to reduce the photon noise, and the high-order aberrations are partly separated from a spot image to well estimate the slope in the subaperture. Simulation results indicate that our method performs better than the weighted center-of-gravity (WCOG) method and correlation method (CM). Under the condition of SNR =20 and r0=13cm The root-mean-square values of the residual wavefront using the proposed method are approximately 10%, 50%, and 35% lower than those of the COG, WCOG, and CM, respectively. The proposed method would be highly beneficial for ground-based astronomical AO systems intended to provide moderate to high Strehl ratios at near infrared wavelengths on larger than 10m-aperture telescopes.

Artificial guide stars for adaptive optics using unmanned aerial vehicles

Astronomical adaptive optics systems are used to increase effective telescope resolution. However, they cannot be used to observe the whole sky since one or more natural guide stars of sufficient brightness must be found within the telescope field of view for the AO system to work. Even when laser guide stars are used, natural guide stars are still required to provide a constant position reference. Here, we introduce a technique to overcome this problem by using rotary unmanned aerial vehicles (UAVs) as a platform from which to produce artificial guide stars. We describe the concept, which relies on the UAV being able to measure its precise relative position. We investigate the adaptive optics performance improvements that can be achieved, which in the cases presented here can improve the Strehl ratio by a factor of at least 2 for a 8~m class telescope. We also discuss improvements to this technique, which is relevant to both astronomical and solar adaptive optics systems.

Christopher Cullen. The Foundations of Celestial Reckoning: Three Ancient Chinese Astronomical Systems. (Scientific Writings from the Ancient and Medieval World.) xi + 434 pp., tables, bibl., index. London/New York: Routledge, 2017. £105 (cloth).

Christopher Cullen. <i>The Foundations of Celestial Reckoning: Three Ancient Chinese Astronomical Systems</i>. (Scientific Writings from the Ancient and Medieval World.) xi + 434 pp., tables, bibl., index. London/New York: Routledge, 2017. £105 (cloth).

Atmospheric turbulence phase screen modeling method based on sub-bands division and multirate sampling

The phase screen method is a well-established approach to analyze the effects of atmospheric turbulence in free space optical (FSO) communication and astronomical imaging system. Owning to the variation of atmospheric turbulence, low complexity modeling is required. Meanwhile, low frequency power should be compensated to overcome shortcomings of classical methods. The method based on sub-bands division and multirate sampling is proposed to solve these problems, and analytic formulas of the model is derived correspondingly. Simulation results are provided to show that our method overperforms the existing methods when both computational complexity and power compensation are taken into account. Furthermore, the proposed method is flexibly in operating which could be used to simulate the base phase screen of time-varying atmospheric turbulence.

Controlling the Laser Guide Star power density distribution at Sodium layer by combining Pre-correction and Beam-shaping

The Sodium laser guide star (LGS) plays a key role in modern astronomical Adaptive Optics Systems (AOSs). The spot size and photon return of the Sodium LGS depend strongly on the laser power density distribution at the Sodium layer and thus affect the performance of the AOS. The power density distribution is degraded by turbulence in the uplink path, launch system aberrations, the beam quality of the laser, and so forth. Even without any aberrations, the TE00 Gaussian type is still not the optimal power density distribution to obtain the best balance between the measurement error and temporal error. To optimize and control the LGS power density distribution at the Sodium layer to an expected distribution type, a method that combines pre-correction and beam-shaping is proposed. A typical result shows that under strong turbulence (Fried parameter (r0) of 5 cm) and for a quasi-continuous wave Sodium laser (power (P) of 15 W), in the best case, our method can effectively optimize the distribution from the Gaussian type to the “top-hat” type and enhance the photon return flux of the Sodium LGS; at the same time, the total error of the AOS is decreased by 36% with our technique for a high power laser and poor seeing.

Dynamics of fragment formation in neutron-rich matter

Background: Neutron stars are astronomical systems with nucleons submitted to extreme conditions. Due to the longer range coulomb repulsion between protons, the system has structural inhomogeneities. Several interactions tailored to reproduce nuclear matter plus screened Coulomb term reproduce these inhomogeneities known as nuclear pasta. These structural inhomogeneities, located in the crust of neutron stars, can also arise in expanding systems depending on the thermodynamic conditions (temperature, proton fraction, ...) and the expansion velocity. Purpose: We aim to find the dynamics of the fragments formation for expanding systems simulated according to the little big bang model. This expansion resembles the evolution of neutron stars merger. Method: We study the dynamics of the nucleons with semiclassical molecular dynamics models. Starting with an equilibrium configuration, we expand the system homogeneously until we arrive to an asymptotic configuration (i. e. very low final densities). We study, with four different cluster recognition algorithms, the fragment distribution throughout this expansion and the dynamics of the cluster formation. Results: Studying the topology of the equilibrium states, before the expansion, we reproduced the known pasta phases plus a novel phase we called pregnocchi, consisting of proton aggregates embedded in a neutron sea. We have identified different fragmentation regimes, depending on the initial temperature and fragment velocity. In particular, for the already mentioned pregnocchi, a neutron cloud surrounds the clusters during the early stages of the expansion, resulting in systems that give rise to configurations compatibles with the emergence of r-proccess. Conclusions: These calculations pave the way to a comparision between Earth experiments and neutron star studies.

A Portable Cosmos: Revealing the Antikythera Mechanism, Scientific Wonder of the Ancient World by Alexander Jones

Reviewed by: A Portable Cosmos: Revealing the Antikythera Mechanism, Scientific Wonder of the Ancient World by Alexander Jones Courtney Roby Alexander Jones. A Portable Cosmos: Revealing the Antikythera Mechanism, Scientific Wonder of the Ancient World. New York: Oxford University Press, 2017. Pp. xiv, 288. $34.95. ISBN 978-0-19-973934-9. The astronomical computer known as the Antikythera Mechanism is of course no stranger to the attentions of both scholarly and popular authors. However, the Mechanism has not been explored at book length by any author with genuine expertise in the Mechanism and the astronomical systems it represents since Derek de Solla Price’s groundbreaking Gears from the Greeks: The Antikythera Mechanism—a Calendar Computer from ca. 80 B.C. (New York 1975). The popular-science writer Jo Marchant’s freewheeling Decoding the Heavens: A 2,000-Year-old Computer and the Century Long Search to Discover Its Secrets (London 2008) sacrifices technical and historical accuracy in service of a fast-paced adventure story (interested readers can find a long list of corrective “comments” on the website of the Antikythera Mechanism Research Project). Meanwhile, Jian-Liang Lin and Hong-Sen Yan’s Decoding the Mechanisms of Antikythera Astronomical Device (sic, Heidelberg 2009) is but another in Springer’s rapidly inflating series of unreliable studies in ancient science and technology written by non-specialists. A Portable Cosmos represents a most satisfying effort to bridge the gap between the broad popular interest that the Mechanism commands and the [End Page 728] technical details of its mechanical and astronomical background. Jones begins with the recent history of the artifact itself: the account of the Antikythera shipwreck’s discovery (including useful context on the other artifacts retrieved from the wreck) and the subsequent waves of reconstruction and imaging that strove to render its fragments intelligible. The remainder of the text is devoted to detailed explanations of the Mechanism and the astronomical phenomena it modeled, breaking down the device’s complexities into individual chapters on the sun and moon, eclipses, the planets, and so forth. A final chapter opens the “black box” of the mechanism to explore the structures and materials of its internal gear systems, while an afterword on “The Meaning of the Mechanism” argues that the Mechanism’s purpose was fundamentally didactic (as opposed to a shipboard navigation system or an astrologer’s calculating tool), situating it alongside other astronomical models like the Archimedean sphaera Cicero describes. The result is a remarkably lucid transformation of the technical details of the Mechanism discovered by Jones and others into a cohesive, robust account of the artifact and its cultural context. Jones’s account is compelling and engaging, inviting the reader to “imagine examining [the Mechanism] for ourselves” (47), describing a sample lesson on calendrical calculations complete with instructions for manipulating the parts of the machine involved in the calculation, and so on. The resulting narrative will thus maintain the reader’s attention even though it is unsparing with technical details. Even readers with minimal prior study of ancient astronomy will want to follow Jones’s explanations of the calculations the Mechanism performed, simply because he makes their cultural stakes so clear. His account of the device’s calendar mechanisms, for example, is firmly rooted in the varied systems of games and festivals that demarcated the year in different parts of the Greek world. Jones draws on textual, material, and epigraphic evidence to populate not just the Mechanism’s cosmos, but also its oikoumenē, with dynamical systems whose movements really mattered to astronomers and laymen alike. Over the past few decades, as new imaging techniques have revealed more of the Mechanism, analyses and reconstructions of its systems have involved their fair share of controversy. Jones deftly weaves these controversies into his account, even in cases where his own views have changed over time, such as the question of what the names of the months inscribed on the calendar suggest about the Mechanism’s provenance. The resulting narrative fights popular assumptions that the process of deciphering the Mechanism has been a matter of proceeding from one truth revealed by new and better imaging techniques to the next, bringing the people and institutions involved in that process...

Опыт применения функции вейвлет преобразования в разработке модели квазигеоида

The article deals with the experience of using satellite methods of determining coordinates based on measurements performed by global navigation satellite systems (GLONASS, GPS, etc.), fundamentallychanging the technology and accuracy of geodetic measurements. For topographic and geodetic production, it is important to establish a connection between the system of geodetic heights obtainedfrom satellite leveling, with a system of normal heights derived from surface geometric leveling. The relationship between geodetic and normal heights is realized through an anomaly of height (the heightof a quasi-geoid), which can be calculated from the results of gravimetric measurements performed on the surface of the Earth or related to its surface. Accurate definition of the height anomaly allows usingsatellite leveling instead of labor-intensive ground leveling. The problem of determining the gravimetric deviations of the plumb line is also urgent; Characteristic of the deviation of the real gravitational&nbsp;field of the Earth from the normal. Components of the plumb deflections are used in solving the reduction problems of higher geodesy, in establishing the connection between astronomical and geodeticcoordinate systems, etc. Classical methods for determining transformants of the gravitational field, based on integral formulas, do not take into account that the initial information is discrete, burdenedby measurement errors and is not known on the entire surface of the Earth. An important requirement of today is a theoretical and practical solution to the problem of determining the transformants of thegravitational field in real time.

Simulations of return flux of polychromatic laser guide stars based on Bloch equations

Sodium laser guide star (LGS) becomes an essential part in modern astronomical adaptive optics system, especially for the next generation extremely large ground based telescope. The LGS technology has experienced the developmental stages as natural guide star, Rayleigh LGS, sodium LGS and constellation of LGS. The sky coverage is still limited in that the LGS cannot not be used to detect the tip/tilt aberrations. While the polychromatic laser guide star (PLGS) is one of the most effective ways to enlarge the sky coverage to 100%. Previous simulation models are insufficient for the accurate calculation of the return flux, especially for the simulation model of PLGS which is generated by one-photon excitation of mesospheric sodium atoms. The simulation model based on Bloch equations proposed in this paper can be used to compute the return flux of one-photon excited PLGS precisely. Doppler broadening, beam atom exchanging, collisions and recoil are taken into account in the model. The return flux is validated by the return efficiency. The simulation results indicate that with one-photon excitation of sodium atoms, a return efficiency of 330 nm is minimum compared with those of other wavelengths; the saturation power density will decrease with recoil increasing and increase with collision rate increasing; an optimal line-width exists up to maximum the photon return efficiency. In the best case, when the power density is 10 W/m2 at the sodium layer, the maximum return efficiency at 330 nm is 0.907 photons/s/sr/atom/(W/m2) with an optimal laser line-width of 18 MHz.

Reducing The Error In The Processing Of Multichannel Correlator Output Signals

Abstract The paper belongs to the field of information and measurement technology and deals with the methods of automated measurement and processing of signals received from monitoring objects for control, surveillance or diagnostics purposes and can be used to process signals from multi-position radar and radio astronomical systems, in particular in systems equipped with correlators for measurement data processing. The object of the invention is to reduce the error in the parameters of the output signal of a multichannel correlator. The proposed method allows ensuring the reliability of information estimators at the correlator output under any conditions, which contributes to the reduction of the error (8-22%) of output data and to adequate decision making in research.

Animation Demonstration System of Astronomical Coordinates

Combining with the fundamental knowledge of astronomy, this paper implements an animation and interactive astronomical coordinates system by employing a series of animation platforms, such as 3D Max9.0 to model and render various types of objects and scenes, the After Effects7.0 for effects processing, the Premiere Pro2.0 for audio and video clipping, Cult 3D 5.3 for the interactive manipulation, and Gaussian simulation 6.5 for the user interface. In this paper, many animation design platforms and techniques have been used to develop a vivid, intuitive, and interactive celestial coordinate demo system, which will help to promote the popularization of astronomy knowledge.

Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

We outline polarization fringe predictions derived from an application of the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder optics. The DKIST retarder baseline design used six crystals, single-layer antireflection coatings, thick cover windows, and oil between all optical interfaces. This tool estimates polarization fringes and optic Mueller matrices as functions of all optical design choices. The amplitude and period of polarized fringes under design changes, manufacturing errors, tolerances, and several physical factors can now be estimated. This tool compares well with observations of fringes for data collected with the spectropolarimeter for infrared and optical regions at the Dunn Solar Telescope using bicrystalline achromatic retarders as well as laboratory tests. With this tool, we show impacts of design decisions on polarization fringes as impacted by antireflection coatings, oil refractive indices, cover window presence, and part thicknesses. This tool helped DKIST decide to remove retarder cover windows and also recommends reconsideration of coating strategies for DKIST. We anticipate this tool to be essential in designing future retarders for mitigation of polarization and intensity fringe errors in other high spectral resolution astronomical systems.

Tidal Love numbers and moment–Love relations of polytropic stars

The physical significance of tidal deformation in astronomical systems has long been known. The recently discovered universal I-Love-Q relations, which connect moment of inertia, quadrupole tidal Love number, and spin-induced quadrupole moment of compact stars, also underscore the special role of tidal deformation in gravitational wave astronomy. Motivated by the observation that such relations also prevail in Newtonian stars and crucially depend on the stiffness of a star, we consider the tidal Love numbers of Newtonian polytropic stars whose stiffness is characterised by a polytropic index $n$. We first perturbatively solve the Lane-Emden equation governing the profile of polytropic stars through the application of the scaled delta expansion method and then formulate perturbation series for the multipolar tidal Love number about the two exactly solvable cases with $n=0$ and $n=1$, respectively. Making use of these two series to form a two-point Pad\'e approximant, we find an approximate expression of the quadrupole tidal Love number, whose error is less than $2.5 \times 10^{-5}$ per cent (0.39 per cent) for $n\in[0,1]$ ($n\in[0,3]$). Similarly, we also determine the mass moments for polytropic stars accurately. Based on these findings, we are able to show that the I-Love-Q relations are in general stationary about the incompressible limit irrespective of the equation of state (EOS) of a star. Moreover, for the I-Love-Q relations, there is a secondary stationary point near $n \approx 0.4444$, thus showing the insensitivity to $n$ for $n\in[0,1]$. Our investigation clearly tracks the universality of the I-Love-Q relations from their validity for stiff stars such as neutron stars to their breakdown for soft stars.

A Scholarly Imprint: How Tibetan Astronomers Brought Jesuit Astronomy to Tibet

The European Jesuits’ mission to China during the seventeenth and eighteenth centuries is considered a world-historical event that played an important role in the transmission of knowledge between the West and the East. In spite of its historical significance, it was long assumed that the Jesuit mission to China and its scientific scholarship had never reached the mountainous regions of Tibet. As I have described elsewhere, this was not the case. Between the eighteenth and nineteenth centuries, Tibetans not only translated a large number of the Jesuits’ works into Tibetan, they also reformed the Tibetan calendar in accordance with the Jesuit-influenced calendar of the Qing. How did it happen and in which way? It was a twofold process achieved partially with Qing imperial sponsorship and partially on the Tibetans’ own initiative, sometimes even in a low-key, indirect and secretive way. In this article, I shall look at how a Tibetan Buddhist astronomer at the imperial court in Beijing wrote a manual for predicting solar and lunar eclipses. I will also look at how some Tibetan astronomers brought this imperial knowledge, apparently without explicit imperial approval, to the monasteries in Amdo, the North-East of Tibet, which mostly lies today in the Chinese provinces of Qinghai and Gansu, as well as how Tibetan astronomers in this region reformed their calendars according to the Jesuits’ astronomical system. Finally, I will describe how this tradition, in spite of recent political upheaval and tragedies, is still alive and practiced in Tibet.

Christopher Cullen, The Foundations of Celestial Reckoning: Three Ancient Chinese Astronomical Systems, London; New York: Routledge (Scientific Writings from the Ancient and Medieval World), 2017, xi, 434 pp.

Christopher Cullen, The Foundations of Celestial Reckoning: Three Ancient Chinese Astronomical Systems, London; New York: Routledge (Scientific Writings from the Ancient and Medieval World), 2017, xi, 434 pp.

Quantisation of the Auxiliary Gravitational Field in Astronomical Systems

Quantisation of the Auxiliary Gravitational Field in Astronomical Systems

Central MONDian spike in spherically symmetric systems

Under a MONDian view, astrophysical systems are expected to follow Newtonian dynamics whenever the local acceleration is above the critical $a_{0}=1.2 \times 10^{-10} m s^{-2}$, and enter a modified regime for accelerations below this critical value. Indeed, the dark matter phenomenology on galactic and subgalactic scales appears always, and only, at low accelerations. It is standard to find the $a<a_{0}$ regime towards the low density outskirts of astronomical systems, where under a Newtonian interpretation, dark matter becomes conspicuous. Thus, it is standard to find, and to think, of the dense central regions of observed systems as purely Newtonian. However, under spherical symmetry in the MONDian as in the Newtonian case, the local acceleration will tend to zero as one approaches the very centre of a mass distribution. It is clear that for spherically symmetric systems, an inner $a<a_{0}$ region will necessarily appear interior to a critical radius which will depend on the details of the density profile in question. Here we calculate analytically such a critical radius for a constant density core, and numerically for a cored isothermal profile. Under a Newtonian interpretation, such a central MONDian region will be interpreted as extra mass, analogous to the controversial black holes sometimes inferred to lie at the centres of globular clusters, despite an absence of nuclear activity detected to date. We calculate this effect and give predictions for the "central black hole" mass to be expected under Newtonian interpretations of low density Galactic globular clusters.

SlicerAstro: A 3-D interactive visual analytics tool for HI data

Abstract SKA precursors are capable of detecting hundreds of galaxies in HI in a single 12 h pointing. In deeper surveys one will probe more easily faint HI structures, typically located in the vicinity of galaxies, such as tails, filaments, and extraplanar gas. The importance of interactive visualization in data exploration has been demonstrated by the wide use of tools (e.g. Karma , Casaviewer , VISIONS ) that help users to receive immediate feedback when manipulating the data. We have developed SlicerAstro , a 3-D interactive viewer with new analysis capabilities, based on traditional 2-D input/output hardware. These capabilities enhance the data inspection, allowing faster analysis of complex sources than with traditional tools. SlicerAstro is an open-source extension of 3DSlicer , a multi-platform open source software package for visualization and medical image processing. We demonstrate the capabilities of the current stable binary release of SlicerAstro , which offers the following features: (i) handling of FITS files and astronomical coordinate systems; (ii) coupled 2-D/3-D visualization; (iii) interactive filtering; (iv) interactive 3-D masking; (v) and interactive 3-D modeling. In addition, SlicerAstro has been designed with a strong, stable and modular C++ core, and its classes are also accessible via Python scripting, allowing great flexibility for user-customized visualization and analysis tasks.