Precision Astrometry Research Articles

Accurate Binary Mass Determinations: Goals, Limitations, and Prospects

The state of the art in accurate mass determination for binary stars is reviewed, and the angular sizes and their errors are computed for a typical system from the existing high-precision sample. It appears that sub-μas (microarcsecond) absolute astrometry will be needed in order to improve the accuracy substantially by astrometry alone. The types of system, and the kinds of data, where precision astrometry appears most promising are outlined. Finally, astrophysical applications of such accurate stellar masses, and the auxiliary data required in them, are briefly reviewed.

PRECISE ASTROMETRY OF HISTORICAL SUPERNOVAE

ABSTRACT Precise astrometric positions of 89 supernovae from the Palomar supernova surveys are presented.

Synthetic curves of some observational properties of contact binary asteroids

The shape of some asteroids may be deduced by other ground based means than rotation light curves or advanced techniques like speckle imaging or radar observations: the analysis of high precision astrometry and lunar occultation light curves. Calculations of the phenomena among the cosmogonically interesting case of a double asteroid configuration, when the objects are in contact with each other, are presented with special emphasis on the involved shadow phenomena.

An Advanced Astrometric Sensor Array

The U.S. Naval Observatory has commissioned the fabrication of an array of six charge-coupled devices (CCDs) bonded to a single silicon substrate for precision astrometry of sources spanning a large range in apparent brightness. The array includes one CCD with rapid readout capability for imaging bright stars. We present the design parameters and the anticipated performance characteristics of this sensor.

Compact non-thermal radio emission from B-peculiar stars

Some stars hotter than 10,000 K show propensity for unusual surface abundances and excessive magnetic fields. These peculiar stars, Ap and Bp in the spectral nomenclature, show unusually prominent absorption lines of heavier elements. Rapid rotation and strong magnetic fields are revealed by line shapes and Zeeman splitting. We have used very-long-baseline interferometry (VLBI) to directly probe the source size and brightness temperature of weak radio emission recently discovered from two isolated Bp stars, σ Orionis E and HD37017. The emitting zone for each star is no more than 6 stellar diameters in extent, reflecting brightness temperatures of more than 109 K. Such high surface brightness resembles gyrosynchrotron radiation from mildly relativistic electrons trapped in the strong magnetic fields surrounding these stars1,2. Compact radio radiation from these two stars presents new opportunities for probing the physical environments of early-type stars and for precise radio astrometry.

Possible binary star progenitor for SN1987A

Accurate optical astrometry gives a position (B 1950.0) for the Large Magellanic Cloud supernova, SN1987A, relative to the FK4 system as right ascension, RA = 05 h 35min 49.95 s± 0.039s (0.21″), declination δ −69° 17′ 57.9″ ±0.27″. Differential astrometry carried out on prime-focus plates taken with the Anglo-Australian telescope indicates that the component, star 1, of Sanduleak's star Sk–69202 is within 0.05±0.13arcs of the super-nova. Here we report that this precision astrometry, together with estimates of the probability of a chance association with a fore-ground or background star, lead us to conclude that the progenitor of SN1987A was star 1 or a fainter binary companion.

Analytical expressions of the Earth's position and velocity for the calculation of apparent positions

In order to calculate the apparent places of stars, the barycentric and heliocentric positions of the Earth and the barycentric velocity of the Earth are required. It is shown that several tens of trigonometric terms for their expressions are sufficient for analyses of optical observations which have an observational accuracy of the order of 0″.001. We also give the analytical expressions of the position and velocity of the Earth with higher precision so that we can use them in the analyses of precise astrometry such as VLBI observations.

Spatial interferometry in the mid-infrared region

The potential of high-resolution spatial interferometry for detailed mapping and precision astrometry in the mid-infrared region, somewhat analogous to interferometry now done in the microwave region, is discussed from an instrumental point of view. Some results from a prototype system and from tests of atmospheric properties are given. The design of a more advanced two-telescope system now under construction is outlined. This involves movable telescopes of 1.65 m aperture and of high precision, using heterodyne detection of infrared in the 10 Μm atmospheric window.

High precision astrometry via very-long-baseline radio interferometry - Estimate of the angular separation between the quasars 1038+528A and B

view Abstract Citations (44) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High precision astrometry via very-long-baseline radio interferometry : estimate of the angular separation between the quasars 1038+528A and B. Marcaide, J. M. ; Shapiro, I. I. Abstract Dual-wavelength VLBI observations with the Mark III system of the two radio quasars 1038 + 528A and B yielded the following relative positions for the epoch 17 March 1981 (1950.0 coordinate system): ΔαB-A = 2s.1205009 ± 0s.0000002; ΔδB-A = 27".1429228 ± 0s.000003 (λ3.6 cm); °αB-A = 2.sl204408 ± 0s.0000006; A = 27".1428622 ± 0s.000009 (λ13 cm). The statistical standard errors represent fractional uncertainties of about 1 and 3 parts in l07 for λ3.6 and λ13 cm, respectively. The position of the brightest CLEAN component was chosen as the reference in each source at each wavelength. The difference found in the separations of these points at the two wavelengths, about 0".10008, is statistically very significant and probably represents the effect of wavelength-dependent opacity in the quasar 1038+528A (Marcaide and Shapiro 1983); plasma refraction contributes negligibly. Earlier, lower precision observations of these sources at these two wavelengths yielded relative positions consistent with those from the March 1981 epoch. Publication: The Astronomical Journal Pub Date: August 1983 DOI: 10.1086/113402 Bibcode: 1983AJ.....88.1133M Keywords: Astrometry; Extragalactic Radio Sources; Quasars; Very Long Base Interferometry; Distance; Separation; Astronomy full text sources ADS | data products SIMBAD (2) NED (1)

Astrometry with the Space Telescope

The Space Telescope offers astronomers for the first time an opportunity to do precision astrometry from space. In this paper, the Space Telescope is described, along with its initial complement of instruments. Particular attention is paid to the Fine Guidance Sensors, which will be the principal astrometric instrument. The responsibilities of the Space Telescope Astrometry Team towards the Space Telescope Astrometry project are described. A description of the scientific results to be expected from Space Telescope astrometry is given. The impact of other proposed Space Astrometry projects, such as the European Astrometry Satellite, on Space Telescope Astrometry is also discussed.

Mutual strategy of search for CETI call signals

A strategy of search for call signals from extraterrestrial intelligence (ETI) is suggested, assuming a mutual desire to communicate. Angular convergence leads to the principle of natural beacons—the directions to the most conspicuous objects of the Universe. On the time axis convergence leads to synchronization of transmission by the observed occurence of Nova (Supernova). Every star receives according to a schedule of the first contract with every other star. An example of a schedule is given, stimulated by Nova Cygni 1975. The schedule conception imposes heavy demands on the precision of astrometry. Fixed and statistical components of the schedule are considered. A small angular vicinity of Nova Cygni 1975 is a potential source of signals from ETI during the next 20–40 years. The Earth must transmit call signals on the day of observation of maximum Nova outburst toward the stars located within a small angular vicinity of the direction antipodal to the Nova. A systematic analysis allows the removal from call signals of the most dangerous anthropomorphims: the type of modulation, the rate of transmission, the codes (languages). It leads to physicomathematical call signals in the form of a product of the physical constant, φ H, and maematical ones (π, 2π, 2 1 2 , 1/π,…) . The precision in the received frequency, πφ H, of monochromatic oscillation is the criterion of intelligence.

Long-baseline radio interferometry with independent frequency standards

The present stage of development of long-baseline interferometry using independent atomic frequency standards is reviewed. The technique is being applied to precision geodesy and astrometry and shows great promise as a means for the intercomparison of national time scales at the 1-ns error level. This paper discusses the development of radio interferometry and, in particular, the theory and practice of interferometry over a very wide (effective) bandwidth. The superb phase stability of the hydrogen maser frequency standard in the range of 100 s to several hours makes it the ideal local oscillator for long-baseline Interferometry.

Can the Fundamental System be Replaced by a Reference System of Galaxies

Quasistellar objects with and without radio emission have recently given unforeseen and vigorous impetus to astrometry. Great effort has been made in the search for the optical counterparts of radio sources. For the purpose of identifications accurate positions were demanded, optical as well as those by radio techniques. Optical positions of radio sources are also needed to serve as calibrators for radio positions. In all cases the objects under consideration are optically much fainter than those ever used previously in high precision astrometry. Finally, methods have been developed for the absolute measurement of radio positions to an accuracy which competes with that known from fundamental observations of bright stars.