Astrometric Observations Research Articles

Asteroid Orbit Determination Using Bayesian Probabilities

We determine asteroid orbital elements from optical astrometric observations using Bayesian a priori and a posteriori probability densities. Assuming Gaussian noise statistics and linearizing the orbit determination problem (linear approximation), a Gaussian a posteriori probability density results for the orbital elements. We develop a Monte Carlo method for the rigorous a posteriori probability density, study non-Gaussian noise and practical orbit determination methods, and describe the difficulties arising from correlated noise and systematic errors. We predict asteroid orbital positions and velocities using the linear approximation and the Monte Carlo approach and give analytically several orbital variances. The variance in the semimajor axis is particularly important: through the mean motion uncertainty, it determines the long-term rate of orbital degradation. In addition, we develop metrics to characterize the overall orbital quality and describe optimization of follow-up observations. Examples are the Jupiter Trojan asteroid (5209) 1989 CW 1, the main-belt asteroid (263) Dresda, the Mars Trojan asteroid (5261) Eureka, and the Apollo asteroid (4179) Toutatis.

VLBI astrometric identification of the radio emitting region in Algol and determination of the orientation of the close binary

A minute displacement of the radio source in Algol was measured by VLBI during two consecutive orbital revolutions of the close binary. The magnitude of the displacement unambiguously indicates that the less massive star of the close binary, a K subgiant, is the star responsible for the nonthermal radio emission of the system. This is consistent with the idea that the radio emission in Algol is related to the strong magnetic activity of the subgiant. The orientation and sense of the displacement on the sky that are directly deduced from our astrometric VLBI observations imply: (1) that the orbital plane of the close binary is at P.A. = +52 deg +/- 5 deg; and (2) that the sense of circulation of the close binary is clockwise, as seen on the sky. Thus, the long-period and close binary orbital motions are almost orthogonal and counterrevolving and this is relevant for evolution and dynamical studies.

Infrared imaging of M CAS B using rapid image motion compensation

We have obtained the first direct images of the low mass companion to Mu Cas A using techniques for high speed correction of image motion at 1.25 and 1.65 micron. These techniques include real-time tracking of the brightest infrared speckle at 75 Hz and of the visible centroid at 500 Hz. Mu Cas B is easily detected with a magnitude difference relative to the primary of greater than 4 at a separation of about 1.4 arcsec. Its energy distribution from 0.55 to 3.4 microns yields an effective temperature (3034 +/- 160 K), stellar diameter (0.26 solar radius), and luminosity (0.0051 +/- 0.0011 solar luminosity). A direct mass measurement using two photocentric orbits yields 0.15 +/- 0.0013 solar mass. Significant improvements in these parameters can result from astrometric, spectroscopic, and imaging observations of the upcoming periastron passage.

Astrometric Observations after 1988.0

Shanghai Observatory has been the institute where astrometric observations are collected and treated after 1988.0, some tables are given here with which one may understand its recent situation.

The Present Status of Preparing the New Reduction of the Past Astrometric Observations to Obtain the Earth Orientation Parameters in the Hipparcos Reference System

The IAU Working group on Earth rotation in the Hipparcos reference frame, set up by IAU Commission 19 in 1988, is presently preparing the algorithms and collecting the data obtained by optical astrometry since the beginning of the century. The main idea is to use the observations of individual stars rather than group results, all recalculated in the unique system of astronomical constants and algorithms. The final solution will be referred to the celestial reference frame realized by the Hipparcos star catalog presently under preparation. All known geophysical influences (as e.g. solid and oceanic Earth tides or plate tectonic movements) will be included into the model. In addition to traditional Earth rotation parameters (polar motion, universal time), also the pole offset components in the celestial reference frame will be solved for, as well as other relevant parameters (systematic seasonal deviations of the individual stations, instrumental constants etc.). The present status of the solution and the time evolution of its expected accuracy are described.

Positional photographic observations of saturn, uranus, neptune, their satellites and pluto in 1990 with the telescope ZTA-2.6 m at byurakan in armenia

Abstract The experimental astrometrical observations in the main focus of the high-lightpower telescope ZTA-2.6 m at Byurakan observatory have been carried out with the aim of providing precise coordinates of the outer planets and their satellites. 5 nights were used for the observations and 38 plates with about 150 images of planets and their satellites were obtained. The “two-step” method of reduction was applied with the FOCAT-S catalogue as a basis. The mean error is ±(0.24 - 0.56) for a single “Satellite minus Satellite” or “Satellite minus Planet” measurement. A strong distorsion of the projection was found in the astrometric treatment of the plates, with the magnitude of the order of 8 × 10−6 mm−2.

Astrometric observations of the faint outer satellites of Jupiter during the 1990-1991 and 1991-1992 oppositions

Plates obtained with a 2.1-m reflector have been measured to obtain astrometric positions for the faint outer Jovian satellites VI-XIII during their 1990-1991 and 1991-1992 oppositions. The tabulation of positions is topocentric astrometric, in a fixed system of the mean equator and with an equinox of J2000.0.

Perturbing Effects in Past Optical Astrometric Data. Statistical Modelisation and Separation

Past optical astrometric observations are to be re-reduced in order to get a new evaluation of the Earth Orientation Parameters in the more accurate Hipparcos reference frame. Among the selected instruments is the Paris astrolabe, considered here. In this Paper, through multivariate statistical procedures, we deal with the preliminary step of the new evaluation which consists in detection and separation of sources of significant inconsistency and outstanding errors in the Paris reductions so far performed. The analysis is performed over two test periods — one per instrumental setting-that are compared in particular in terms of observer effects, magnitude, colour and sidereal time effects. The Paper also gives a synthetic overview on the statistical methods we used to obtain the main results so that they can be applied to other astrometric data.

An estimation of the oblateness of Sun from the motion of Icarus

From astrometric observations of minor planet (1566) Icarus from 1949 to 1987 were made solutions for improved orbital elements of Icarus and the quadrupole moment of the Sun. The formal result was J2 = -0.6±5.8 &d 10−6. From this we can conclude that J2 is very probably less than 2 · 10−-5.

On the relativistic motion of (1566) Icarus

We collected 727 astrometric observations of Icarus from the interval 1949-1987 to use them for the orbit improvement when studying the motion of the asteroid. To verify the predictions of the general relativity, we determined the relativity factor λ included to the equations of motion; we used the simple form of relativistic equations of motion written in the Painleve's coordinates, and based on the solution of one-body Schwarzschild problem. We also made an attempt to determine nongravitational effects which appeared to be insignificant in the Icarus' motion

Microarcsecond astrometry in space - Relativistic effects and reduction of observations

view Abstract Citations (86) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Microarcsecond Astrometry in Space: Relativistic Effects and Reduction of Observations Klioner, S. A. ; Kopeikin, S. M. Abstract The paper applies the framework of general relativity to the problem of reduction of high-precision astrometric observations of the order of 1 microarcsec. Theoretical methods making it possible to construct astrometric reference systems involving the barycentric, geocentric, and satellite (observer) systems are described. Relativistic transformations between the reference systems employed are derived. Equations of geometric optics for the nonstationary gravitational field of the solar system are deduced. The effects of relativistic deflection of the light due to monopole and quadrupole components of the sun's gravitational field and the planets are calculated, with their motions and rotations taken into account. Transformations between the reference systems are used to calculate the light aberration occurring when passing from the satellite system to the geocentric system and from the geocentric system to the barycentric systems. Aberrational corrections are applied to transform the observed position of a celestial object to the barycentric system, taking the relativistic light deflection into account. Publication: The Astronomical Journal Pub Date: August 1992 DOI: 10.1086/116284 Bibcode: 1992AJ....104..897K Keywords: Astrometry; Celestial Reference Systems; Relativistic Effects; Relativity; Computational Astrophysics; Gravitational Fields; Perturbation Theory; Solar System; Stellar Parallax; Astronomy; ASTROMETRY; RELATIVITY; TECHNIQUES: INTERFEROMETRIC full text sources ADS |

THE ORBIT AND MASS OF PROCYON

ABSTRACT We have determined the orbit and parallax of the Procyon system (F5 IV-V primary and white dwarf secondary) using conventional absolute radial velocities, precise relative radial velocities determined with the hydrogen flouride (HF) absorption-cell technique, and astrometric and visual observations. Our least-squares analysis confirms and strengthens Strand's previous analysis based on more limited material. We derive an absolute parallax of piabs=0.2899 ± 0.0074 arcsec. Our parallax result is in excellent agreement with other parallax investigations based on independent material. If we adopt the latest USNO parallax of piabs=0.2864 ± 0.0023 arcsec, then from our orbital paramters we derive MA=1.751 ± 0.051 solar mass, and MB=0.622 ± 0.017 solar mass. For the derived mass of Procyon A (which is consistent with previous results), it has long been known that the luminosity predicted by stellar interior theory is approximately a factor of two larger than the luminosity derived from observations. The errors in this observed luminosity and the above formal standard errors (i.e., our best estimates of the statistical random errors) in our derived mass are too small to explain this discrepancy. If the observed separation of the binary components has been systematically overestimated by approximately 0.2 arcsec, then the derived mass would be reduced, thus resolving the discrepancy. However, the excellent consistency of the separations measured by Aitken and Barnard for a number of years at different sites argues against this interpretation. The stellar interior theory of Procyon A may need substantial revision.

The masses of Uranus and its major satellites from Voyager tracking data and earth-based Uranian satellite data

Improved values for the masses of the Uranian system and the satellites Ariel, Umbriel, Titania, Oberon, and Miranda are obtained on the basis of an analysis of the Doppler-tracking data and star-satellite imaging from the Voyager 2 spacecraft combined with earth-based astrometric satellite observations. Masses are expressed as the product, the universal gravitational constant times the mass of the body, in units of (cu km/sq s). The satellite masses are (4.4 +/- 0.5) for Miranda, (90.3 +/- 8.0) for Ariel, (78.2 +/- 9.0) for Umbriel, (235.3 +/- 6.0) for Titania, and (201.1 +/- 5.0) for Oberon. Quoted errors are standard errors and are the present assessment of the true rather than the formal errors. The Uranus rotational pole orientation angles and gravity harmonic coefficients were fixed at the values determined by French et al. (1988) from stellar occultations of the Uranian rings observed from both the earth and Voyager 2 and from the occultation of the spacecraft radio signal.

A PRECISE RADIAL-VELOCITY DETERMINATION OF THE ORBIT OF CHI-1 ORIONIS

ABSTRACT We have determined a precise orbit of Chi-1 Orionis (G0 V, MV = 4.4) using radial velocities observed with our HF absorption-cell technique and previous Sproul astrometric observations. Least-squares analysis yields a photocentric semimajor axis alphap = 0.082 ± 0.004 arc-seconds, a radial-velocity amplitude K = 1886 ± 6 m s-1, and a period P = 14.21 ± 0.06 years. Our results imply the secondary has a mass of 0.15 ± 0.01 solar mass, the minimum parallax of the system is pi = 0.102 ± 0.005 arc-seconds, and the secondary is fainter than MV = 8.8.

Astrometric observations of the faint outer satellites of Jupiter during the 1989-1990 opposition

Astrometric observations of the faint outer satellites of Jupiter during the 1989-1990 opposition

Stellar Masses from Double Star Observations with the Mark III Interferometer

AbstractBy improving on the angular resolution possible with conventional telescopes, speckle interferometry has been adding to the list of known masses, resolving binaries with separations of 30 mas. Interferometry with separate apertures offers the possibility of going to much higher resolution.The Mark III Optical Interferometer on Mt. Wilson has been used for astrometry, for stellar diameter measurements, and for binary observations since routine operations began in late 1988. The fringe visibilty calibration uncertainty is ~1% for m < 4m at λ800 nm with good seeing, so that both binary components can be detected when the magnitude difference is 3.5m to 4m.From Mark III data, masses of eight stars have been determined. The most precise determination is for the components of the ϕ Cygni system: 2.545 ± 0.085 and 2.445 ± 0.081 M⊙. To improve on this measurement, more precise spectroscopic data are needed, as is the case for most of the systems for which we have orbits or preliminary orbits.The NRL/USNO Optical Interferometer Project is currently designing two more capable instruments: a four–element system for astrometric observations, and a six–element system for imaging. The ultimate 430-m maximum baseline and 35-cm apertures of the imaging interferometer will allow observations to 8th to 10th mag and resolution of binary components separated by as little as ≈ 200 µas.

Pluto-Charon stellar occultation candidates - 1990-1995

We have carried out a search to identify stars that might be occulted by Pluto or Charon during the period 1990-1995 and part of 1996. This search was made with an unfiltered CCD camera operated in the strip scanning mode, and it reaches an R magnitude of approximately 17.5-about 1.5 mag fainter than previous searches. Circumstances for each of the 162 potential occultations are given, including an approximate R magnitude of the star, which allows estimation of the signal-to-noise ratio (S/N) for observation of each occultation. The faintest stars in our list would yield an S/N of about 20 for a 1 S integration when observed with a CCD detector on an 8 m telescope under a dark sky. Our astrometric precision (+/- 0.2 arcsec, with larger systematic errors possible for individual cases) is insufficient to serve as a final prediction for these potential occultations, but is sufficient to identify stars deserving of further, more accurate, astrometric observations. Statistically, we expect about 32 of these events to be observable somewhere on Earth. The number of events actually observed will be substantially smaller because of clouds and the sparse distribution of large telescopes. Finder charts for each of the 91 stars involved are presented.

Astrometric observations of the faint outer satellites of Jupiter during the 1988-1989 opposition

Astrometric positions for the faint outer Jovian satellites VI-XIII during the 1993 opposition have been obtained from the measurement of plates taken with the 2.1 m Otto Struve reflector at McDonald Observatory.

Dynamical states and dynamical evolution of the selected triple star systems

The general problem of investigating multiple stellar systems is formulated. It is shown that the complete solution of this problem requires 1) a complex of astrometric and astrophysical observations of multiple stars, and the 2) maximum attainable precision of such observations. The conditions under which this precision can be achieved are discussed.

Parametric adjustment of absolute astrometric observations

The least-squares parametric method which is well-known in geodesy is suggested to be used for adjustment of the absolute astrometric observations. This method most completely uses all results of the observations, their mutual covariances and a priori data about an accuracy of the initial catalogue. The method ensures the most precise estimates of unknown parameters and has an objective criterion for the reliability theirs. The application of this method in case of traditional chain programs of optical observations was considered in details. It is recomended that the covariance matrix of the FK4 systematic errors parameters would be calculated and published in the compilation of the FK5.