Astronomical Systems Research Articles

Astronomical units and constants in the general relativity framework

An attempt is made to analyze the existing system of astronomical constants within the general relativity theory (GRT) framework. The general conclusion is that, to avoid any confusion in the GRT compatible interpretation of units and constants, one should give precisely, with full post-Newtonian accuracy, the expressions of the metric forms describing the astronomical barycentric and geocentric reference systems used, for example, in IERS analysis of observations.

Unstable objects in the galaxy and the star-formation process

Using observational data, we consider the problem of instability of astronomical objects and systems of objects and its close connection with the star-formation process. We show that it is only due to the discovery and study of stellar associations that the enormous role of stellar instability in the formation of stars in the Galaxy (and in other galaxies) has been definitively explained. Many kinematic properties of stellar associations are inexplicable from the old point of view. This gives grounds for doubting the correctness of the classical hypothesis that stars form from diffuse matter.

Progress and prospects in neutrino astrophysics

The neutrino deficits observed in four solar neutrino experiments, relative to the theoretical predictions, have led to fresh insights into neutrino and solar physics. Neutrino emission from distant, energetic astronomical systems may form the basis for a new field of astronomy. Additional experiments are needed to test explanations of the solar neutrino deficits and to allow the detection of more distant sources.

Imaging the universe at radio wavelengths

Computerized image processing is crucial for the large arrays of radio telescopes that are advancing astronomy. A new project will help relieve the computational bottleneck that hinders this field. The National Science Foundation (NSF) has funded a 5-year Grand Challenge High-Performance Computing and Communications project to (a) allow astronomers to use upgraded NSF supercomputers; (b) develop network links to widely-used observatories; and (c) develop digital data archives over national high-speed networks. We plan to prototype the next generation of astronomical telescope systems. These will be remotely located telescopes connected by high-speed networks to very high performance, scalable-architecture computers and online data archives. Astronomers will access these systems via gigabit-per-second networks, and use advanced visualization tools to comprehend and analyze the very large multidimensional images being generated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The CCD Array Camera for the Macho Project

We have developed an astronomical imaging system tailored to our search for gravitational microlensing by compact objects in the halo and disk of the Galaxy. The challenge of detecting rare microlensing events is to monitor ∼ 10 million stars per night and distinguish genuine events from other sources of variability. The Large Magellanic Cloud and the Galactic bulge provide the high surface density of resolvable stars necessary for this task. A dedicated 50 inch telescope at Mt. Stromlo Observatory has been producing science data since the fall of 1992. Our system incorporates eight 2048 × 2048 CCDs into two focal planes for simultaneous imaging in two passbands (4500–6300 and 6300–8100 å). Each focal plane consists of four ‘edge-buttable’ CCDs in a custom mounted 2 × 2 array. The 0.62 arcsecond pixel scale (15 μm) yields a 40 × 40 arcminute square field of view in each frame. A sophisticated point spread fitting photometry package extracts up to 600,000 useful magnitudes per color per frame. The data collection rate we need is obtained by simultaneously reading out all sixteen CCD outputs (two per chip) at 34 KHz with 16 bit digitization. With exposure times of 150–300 seconds and a 70 second readout time we can collect up to 100 fields per night. These rates are designed to allow us to detect or rule out massive compact halo objects (MACHOs) in the 10−6–101 M ⊙ range.

Relativistic theory of astronomical reference systems in closed form.

The present paper extends the asymptotic matching techniques developed by Brumberg and Kopejkin as applied to the relativistic theory of astronomical reference systems, in the following principal aspects. (1) The full post-Newtonian expressions for the gravitational field in the geocentric reference system are given in closed form. This cancels the necessity to use a post-Newtonian analogue of the "tidal" expansion in powers of local spatial coordinates to represent the gravitational field of the external masses (such as the Sun). A finite expression, analogous to the classical third-body perturbation function, can be used instead. (2) Our approach, being initially developed in harmonic coordinates, can be easily reformulated in other most frequently used gauges. The corresponding transformation formulas in the case of the standard parametrized-post-Newtonian gauge are derived. (3) In applying our theory to astronomical problems, the equations of motion of an Earth satellite are derived with the use of the geodetic principle. We do not neglect herewith relativistic terms proportional to the nongeodesic acceleration of the Earth. A practically important improvement of some previous results is obtained. The results of this paper are thoroughly compared with those derived by Brumberg and Kopejkin in terms of multiple expansions.

Chemistry and cosmology

This paper offers a theoretical interpretation of two apparently unrelated numerical coincidences. (1) The observed range of specific gravitational binding energies in astronomical systems includes the range of specific cohesive energies of solids. For example, the planetary system has about the same binding energy per unit mass as a molecular solid. (2) The present age of the universe, measured in units e 2 /m e c 3 , is roughly equal to the ratio between the electrostatic and gravitational interactions between a proton and an electron. Both coincidences are explained by a cosmological theory based on Einstein's theory of gravitation, the cosmological principle (statistical uniformity and isotropy), and the assumption that the universe began to expand from a maximally dense initial state at zero temperature

Automated Optical Identifications of Radio Sources

AbstractThis paper evaluates the COSMOS database as a tool for large-scale automated optical identification programs. Firstly, we explore the limitations inherent in the database by a study of regions centred on clusters of galaxies. We then perform an automated search in the database for a sample of previously measured optical objects and compare the properties of corresponding objects. Finally, we describe a set of new plotting routines in AIPS (Astronomical Image Processing System) designed to plot COSMOS-derived ellipses and, optionally, magnitudes onto radio images.

A Computational Study of the Dynamical Evolution of Self-Gravitating Systems

We have developed a computing procedure to study the dynamical evolution of self-gravitating astronomical systems. It is based on a stochastic model which is a generalization to the multimass and anisotropic case of the Fokker-Planck equation moment method. In this paper we present the main characteristics of the model and the computing procedure. We also present a practical application of the method.

VMEBUS SYSTEM FOR CCD IMAGE ACQUISITION

ABSTRACT We describe the astronomical image acquisition system developed at Catania Astrophysical Observatory, based on a VMEbus and the Motorola MVME-147 Single Board Computer (SBC) running the real-time OS-9/68000 Professional operating system. Also described are the hardware architecture chosen and the software strategies used for the image acquisition from a CCD controller with improved flexibility and speed of the operation. The CPU directly controls data acquisition in sychronization with the CCD electronics, by disabling the operating system and running an assembler program, which allows us to use only three standard VME boards and guarantees a high throughput and high data accuracy.

ERRORS ASSOCIATED WITH FITTING GAUSSIAN PROFILES TO NOISY EMISSION-LINE SPECTRA

ABSTRACT Landman, Roussel-Dupre, and Tanigawa developed prescriptions to predict profile fitting errors for Gaussian emission lines perturbed by white noise. We show that their scaling laws can be generalized to more complicated signal-dependent "noise models" of common astronomical detector systems.

A microstep controller of a DC servomotor

A microstep controller of a DC servomotor is developed for accurate positioning and smooth movement at low-speed rotation. It consists of digital and analog positioning loops. Dividing one period of quadrature sinusoidal signals generated by an incremental encoder attached to a motor shaft into quarter sections, the digital loop controls the movement between the sections. The analog loop divides each section further into N equiangle segments to control the movement within each section. The effective angle resolution is thus 90 degrees /MN with M being the number of slits etched on an incremental encoder. A prototype controller assembled using monolithic and hybrid integrated components has confirmed the principles of operation. Positioning accuracy was 0.009 degrees +or-0.002 degrees . A further improvement is possible with this controller by increasing the number of slits on the encoder and reducing the interpolation step size. Positioning accuracy is dominated ultimately by the amplitude fluctuation of quadrature sinusoidal outputs, and thus an automatic amplitude control should be incorporated into the encoder. The controller was first intended for applications such as crystal-pulling apparatus, astronomical observation systems, and tracking radars, which require smoothly rotating mechanisms, but it can also be applied to fine-positioning mechanisms in scanning electron and tunneling microscopes and semiconductor manufacturing equipment. >

The emission spectrum of C 2N 2

Cyanogen absorption, excitation and dispersed fluorescence spectra have been measured in the 220 nm region. The radiative lifetime is 1.34 μs under collisionless conditions. The fluorescence spectrum following excitation of the 4 0 1 band consists of four simple progressions. No CN radical fragments were detected following absorption at 220 nm. This clearly demonstrates the bound nature of the lowest vibrational levels of the A 1Σ u − electronic state. The emission could be used for remote detection of cyanogen in astronomical systems.

Astrophysical APL - diamonds in the sky

Computational astrophysics seeks to develop numerical models which help elucidate the nature of astronomical systems. Such models must not only adequately describe the underlying physics which give rise to phenomena that have been observed, but must also be predictive in asserting what future observations might unfold. Any model which is in conflict with physical observations, clearly, must be discarded or amended to reflect reality. As a computational modelling tool we find APL useful for testing astrophysical hypotheses, and extending the domain of our observationally based knowledge. Using APL to build, test, and expand astrophysical models frees the investigator from the mechanical drudgery of computer programming, thereby allowing the researcher to concentrate on understanding the physical universe.As a quantitative example of how relatively complex astrophysical phenomena can be explored with ease using APL, we have developed a structure model for white dwarf stars. The model presented here considers such effects as Coulomb interactions between electrons and nucleons, inverse beta decays, and the effects of the general theory of relativity on the condition of hydrostatic equilibrium. This structure model is valid for zero-temperature stars of varying chemical compositions, ionic partitions, and central densities; and is applicable over a wide range of partial and total degeneracy regimes.

Library and Information Services in Chinese Astronomy

The development of the library science marks the progresses of science and culture in a country or a district. The study courses and results of a research institute are strongly reflected by its library and information work. The development of the astronomical research, the collection of astronomical observations, and the manufacture of astronomical instruments and equipments, etc., are all being made progress by library and information services to consult scientific foundation, to seek method, and to derive needed nourishment. The astronomical library and information service system is growing and expanding with continuously providing information to the astronomical study. In this paper I shall give some introductions about the Libraries and Information Divisions of astronomical observatories in our country.

Gamma-ray bursts and glitching neutron stars

Gamma-ray bursts, short flashes of nonthermal radiation, may shed light on the structure and formation rate of neutron stars. At least one and possibly all gamma-ray bursts originate from neutron stars, and the study of the mechanisms for generating bursts may elucidate the internal structure of these stars and, hence, the properties of high-density matter. This report summarizes salient observations of gamma-ray bursts and considers whether there is more than one class of gamma-ray burster and in what ways other astronomical systems have observed properties that resemble gamma-ray bursts. It then examines physical constraints on neutron star models of gamma-ray bursters and explores a particular model in which crustal glitches in neutron stars produce gamma-ray bursts.

The Role of Number in Philolaus' Philosophy

Philolaus is a peripheral figure in the history of Greek mathematics. We know of no important advance in mathematics that is attributed to him, nor is there any evidence that he wrote a book exclusively or even primarily devoted to mathematical topics.' Indeed the tradition about Philolaus suggests that he wrote just one book and not a terribly long one at that.2 What is known of that book from fragments and testimonia suggests that it covered a wide range of topics despite a relatively small compass. There is evidence that after an account of the basic principles of the cosmos Philolaus went on to present his own astronomical system, his own views on the different psychological faculties of human beings, and a theory of the constitution of the human body and the origins of disease.3 Moreover, mathematical ideas were prominent. The whole number ratios that determine the concordant musical intervals are mentioned in Fragment 6 while other fragments are concemed with number (Fragments 4 and 5) and include a classification of number into two primary types (odd and even)

Global Fringe Fitting for Space Interferometry

The technique of global fringe fitting has proven to be very valuable for very-long-baseline interferometry (VLBI). It allows weaker fringes to be detected than is possible with conventional single-baseline fringe fitting algorithms, and thus improves the sensitivity of present VLBI arrays. Global fitting was developed for VLBI by Schwab and Cotton (1983, Astron. J.88, 688), and has been incorporated into the NRAO Astronomical Image Processing System as program VBFIT. As Schwab and Cotton point out, this is a generalized from of self-calibration in which closure relations for residual fringe delay and rate (frequency) are satisfied in addition to those for fringe phase and amplitude. These additional closure relations allow station-dependent delays and rates to be solved for, using data from all baselines with sufficiently strong fringes. Then it is possible to calculate where fringes will be on any less sensitive baselines between these telescopes, so that very narrow search windows in delay and rate can be used.

The pierce-blitzstein stellar radiometric system

Throughout the development of the system, since its initiation in the 1940's, the philosophy has been to (a) take advantage of any new technological advances which become available commercially, (b) develop auxiliary testing facilities for the components of the system, (c) pursue a continuous theoretical and experimental analysis of the system in order to verify all significant specifications, (d) verify by astronomical observation that the predictions of the system analyses are valid. The author believes that this review of the development of the system and a theoretical and/or experimental analysis will be instructive to others involved in the design and use of astronomical radiometric systems.

The reference frame of the ephemerides

Complete ephemerides of the moon and the four inner planets could be created solely from ranging data alone. Such ephemerides would then be independent from any outside astronomical reference system, and, therefore, would define their own unique reference frame. In fact, this is nearly the case with present-day ephemerides; the accuracy of the ranging data tends to dominate most of the least squares adjustment.This paper outlines the process of creating the lunar and planetary ephemerides along with the orientation of the ephemerides onto the dynamical equinox. The resulting accuracies of these processes are given and a number of uses for the ephemerides are highlighted.