Modern methods in the astrometry of double stars

The techniques for studying double stars continue to evolve in a predictable way. The most recent major breakthroughs have been the area scanner and speckle interferometry. On the horizon looms the application of large format CCDs which will replace the photographic plate for many astrometric problems.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

Random errors of star abscissae in the ROEMER space astrometry project

We discuss the propagation of random errors in the so-called great-circle reduction of the Hipparcos mission and for the proposed space astrometry project ROEMER. As a step towards the determination of stellar positions, proper motions and parallaxes, one-dimensional instantaneous relative positions of stars along fixed great circles are estimated from elementary measurements of the locations of stellar images within the instrument's field of view. The measurement errors, being dominated by photon noise, can be regarded as uncorrelated. The precision of the calculated one-dimensional positions (abscissae) depends on the precision and number of elementary measurements, the number of stars and their distribution in magnitude, and finally on the rigidity of the great-circle reduction. The rigidity quantifies how well the random measurement errors are averaged out in the least-squares solution, and is closely related to the condition number of the design matrix. We discuss the rigidity concept for idealised situations involving one, two, or several fields of view (zero, one, or more basic angles). A simple model of the error propagation is derived and used to predict the precision for a hypothetical space astrometry project such as ROEMER. It is found that the rigidity is much improved by the greater number of stars observed with ROEMER.     

The visual double star data base

Any use of stars for astrometric purposes necessarily involves examination of their duplicity characteristics. The Washington Double Star Catalog (WDS) provides this information in a continuously updated and machine-readable format. This contribution describes the current data base and plans for its future extension.     

Relativistic astrometry

Concepts of relativistic astrometry — such as Weyl's stellar compass or the concept of flat-space plus forces — are discussed. To visualize effects from light deflection pictures showing the stellar sky as seen from the vicinity of a strongly gravitating source are presented.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

CCD observations of the star formation region NGC 7129

CCD images of NGC 7129 were carried out in July 1988. These observations have better spatial resolution than former ones. Several Herbig-Haro objects and reflection nebulae have been observed. Some of these objects are new detections; in addition, we find new structures in previously known NGC 7129 nebulosities.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

CCD Photometry of the W UMa type star QX Andromeda

We present new B- and V-band photometry of the W UMa-type binary system QX And, which is a member of the open cluster NGC 752. Revised orbital period and new ephemerides were given for the binary system based on the data of times of light minima. The result of a period analysis reveals that the system is undergoing a continuous orbital period increase during the past decades. The rate of period increasing turns out to be about 2.7 × 10^?7 d yr^?1. With the Wilson–Devinney code, a photometric solution is computed. It yields a contact configuration for the system with a filling factor of 0.361. Combining the results from the photometric solution along with that from the radial-velocity observations, we have determined the absolute parameters for the two components of the system. The masses, radii and luminosity of the primary and secondary stars are calculated as 1.43 ± 0.04 M_⊙, 1.45 ± 0.09 R_⊙, 2.87 ± 0.40 L_⊙ and 0.44 ± 0.02 M_⊙, 0.87 ± 0.05 R_⊙, 0.99 ± 0.13 L_⊙, respectively. The evolutionary status and physical nature of the contact binary system were discussed compared with the theoretical models.     

On the determination of double star orbits

It is proposed to improve the convergence of the determination of the elements of the orbits of visual binaries by using not only first, but second-order derivatives in the development of the appropriate equations of condition. Also, some improvements of the Kowalsky-Seeliger method are suggested which improve the accuracy of the orbit used as first approximation.     

Solar astrometry by photolithography

Observed temporal variations of shape and size of the solar disk as viewed from Earth may act as constraints for theories of the interior of the Sun. In addition to existing programs of solar diameter measurements we investigate a ground-based photographic method.The solar limb profile is recorded on a photoresist-coated substrate over a 20 radial length simultaneously all along the circonference as a three-dimensional 21 mm diameter, 0.0015mm thick permanent object available for inspection by interferometric methods. The exposure time is long enough for filtering much of the atmospheric turbulence, whereas the slope of the observed solar limb should help to locate a standard solar limb. The first results of February 1989 at large zenith distance and low altitude are a set of differential measurements of the position of a solar limb around a circle with, after taking into account the 3.7 atmospheric differential refraction, a 0.34r.m.s. dispersion of the residuals for a fit to a circular solar disk.We estimate that this method of accuracy comparable to other ground-based methods, with potentially more than 600 independent simultaneous measurements along the circonference, could help to discriminate between terrestrial and solar causes for variations of shape and size of the solar disk.We note that operation outside the Earth's atmosphere would provide access not only to undisturbed images but also to UV wavelengths, i.e., to a better definition of the solar limb.     

Precision astrometry with SuperCOSMOS

We describe the new, fast, high-precision microdensitometer SuperCOSMOS. Some aspects of hardware and software design that enable high-precision astrometry from photographic plates are explained. We show that the positioning repeatability of the measuring machine is less than 0.1 μ μ m standard error in either coordinate, and the absolute positional accuracy is about 0.15 μ m standard error. Furthermore, measurements of the same plate in different orientations show that the sampling errors are small (e.g. ∼ 0.2 μ m, rising to ∼ 1.0 μ m at the plate limit, for stellar images in a IIIaJ emulsion), thus allowing the extraction of relative positional information from Schmidt plates at accuracies less than 1 μ m. We demonstrate that SuperCOSMOS is capable of measuring the positions of bright stars (i.e. those more than ∼ 4 mag above the plate limit) to a precision ∼ 0.5 μ m with survey–grade photographic plates employing fine–grained emulsions.     

A development of double star astronomy after Hipparcos

Now that the HIPPARCOS satellite safely revolves on his degraded orbit - after the exploit of the ESA technicians to rescue it from the faulty ignition of its apogeum boost motor - and regularly provides the information needed for reaching the initial aim of the project, one may turn to examine the possible applications of the finalHipparcos Catalogue. In the present paper, we describe how double and multiple stars have been introduced in the Input Catalogue and what may be expected from their observation. We also try to evaluate how much the final HIPPARCOS data may influence future researches on these celestial bodies and what kind of ground-based observation programmes should be conducted in order to support the space results.This paper was presented at the IAU Colloquium No. 135 (Complementary Approaches to Double and Multiple Star Research) at Pine Mountain (Georgia, USA) in April 1992 by J. Dommanget and at the Ecole de Goutelas (HIPPARCOS: Une nouvelle donné pour l'astronomie) at Boën (France) in May 1992 by P. Lampens. Extended summaries will be published in both proceedings.     

Observational signature of a wind bubble environment for double neutron star mergers

During the in-spiral stage of a compact binary, a wind bubble could be blown into the interstellar medium, if electromagnetic radiation due to the binary orbital motion is strong enough. Therefore, shortduration gamma-ray bursts(SGRBs) due to double neutron star mergers would in principle happen in a wind bubble environment, which can influence the propagation of the SGRB jet and consequent afterglow emission. By calculating the dynamics and synchrotron radiation of the jet-driven external shock, we reveal that an abrupt jump could appear in the afterglow light curves of SGRBs and the observational time of the jump is dependent on the viewing angle. This light curve jump provides an observational signature to constrain the radius of the wind bubble and thus the power of the electromagnetic radiation of the binary,by combining with gravitational wave detection.     

Microarcsecond astrometry using the SKA

The sensitivity and versatility of SKA will provide microarcsec astrometric precision and high quality milliarcsec-resolution images by simultaneously detecting calibrator sources near the target source. To reach these goals, we suggest that the long-baseline component of SKA contains at least 25% of the total collecting area in a region between 1000 and 5000 km from the core SKA. We also suggest a minimum of 60 elements in the long-baseline component of SKA to provide the necessary (u–v) coverage. For simultaneous all-sky observations, which provide absolute astrometric and geodetic parameters, we suggest using 10 independent subarrays each composed of at least six long-baseline elements correlated with the core SKA. We discuss many anticipated SKA long-baseline astrometric experiments: determination of distance, proper motion and orbital motion of thousands of stellar objects; planetary motion detections; mass determination of degenerate stars using their kinetics; calibration of the universal distance scale from 10 to 10⁷ pc; the core and inner-jet interactions of AGN. With an increase by a factor of 10 in absolute astrometric accuracy using simultaneous all sky observations, the fundamental quasar reference frame can be defined to <10 μas and tied to the solar-system dynamic frame to this accuracy. Parameters associated with the earth rotation and orientation, nutation, and geophysical parameters, can be accurately monitored. Tests of fundamental physics include: solar and Jovian deflection experiments, the sky frame accuracy needed to interpret the gravity wave/pulsar-timing experiment, accurate monitoring of spacecraft orbits that impact solar system dynamics.     

Geodynamic implications of astrometry

The transition from local horizon and terrestrial BIH-systems to celestial reference frames is well known to be affected by various geodetic parameters such as polar motion (x_p(t), y_p(t)), UT1-TUC (where UT1 is basically dependent on variations in UT0 and t=time), plumb line deflections (, ) of observation stations, global and local tidal deformations etc. Variations of such quantities with (relative) resolution of the order of 0.001 and better, such as VLBI, demand the application of continuous high-precision (world-wide) geodynamic surveys whenever global theories and sufficient models are not available and the introduction of improved local and global models (geophysical and relativistic) is needed in order to match astrometric observations related to different reference frames. Prediction of parameters for immediate transformation from one system of reference into the other is sometimes of interest.The paperreviews recent results of different observations,points out a number of still open and unresolved problems in observations and modeling, anddiscusses related consequences. Conclusions for geodynamics drawn from comparison of observed data with models based on astronomical and geophysical observations give way to new understanding of basic phenomena of relevance for various disciplines.     

On the analytic calculation of visual double star orbits

This article studies the existence of periodic Keplerian orbits for visual double stars whose corresponding apparent orbits are to pass through three selected points. The analytical results provide the basis for a new method of calculating orbits which does not require prior calculation of the areal constant. This method is applied to the binary 04404 N 4313.     

Physical conditions in the compact double star HD 187399

We present the results of a study of the spectra of the compact double system HD 187399. We have measured and identified lines in the spectrum of the main star and computed their equivalent widths, the central residual intensities, and the electron densities in the atmosphere of the main star and the common envelope of the system. We have constructed the curve of radial velocities of the main star and determined the expansion velocity of the common envelope of the system: v_r =90 km/sec. We have measured the velocity of the interstellar calcium: v_r =–3.5 km/sec. We have established the agreement of the radial velocity curves for the main star obtained in the present paper and in that of Merrill [1]. The comparison enabled us to make the following conjecture: there has been no noticeable loss of mass in the system HD 187399 over the past 35 years, and possibly all that has occurred is a flow of matter from one component toward the other. We note the strong similarity with the Lyrae system.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

The mass/eccentricity limit in double star astronomy

A research that we conducted in 1963 on the evolution of the binaries based on the available orbital data to obtain a philosophical degree, led to the establishment of an interesting and new diagram between the logarithm of the total mass and a particular parameterX, bound to the areal constant. This appeared to have a real physical significance but the basic observational material was insufficiently extended to assure its undeniable existence. In 1981, a new research based on a more extended orbital material, has confirmed this diagram. Presently, another important increase in the orbital material and the availability of highly accurate trigonometric parallaxes produced by the Hipparcos satellite, gave us the opportunity to confirm once more the stability of this diagram. This last research is here described.