A. Lopez Garcia

Figures of equilibrium in close binary systems

The equilibrium configurations of close binary systems are analyzed. The autogravitational, centrifugal and tidal potentials are expanded in Clairauts coordinates. From the set of the total potential angular terms an integral equations system is derived. The reduction of them to ordinary differential equations and the determination of the boundary conditions allow a formulation of the problem in terms of a single variable.The equilibrium configurations of close binary systems are analyzed. The autogravitational, centrifugal and tidal potentials are expanded in Clairauts coordinates. From the set of the total potential angular terms an integral equations system is derived. The reduction of them to ordinary differential equations and the determination of the boundary conditions allow a formulation of the problem in terms of a single variable.

Automatic measurement of images on astrometric plates

Abstract We present some results on the process of automatic detection and measurement of objects in overlapped fields of astrometric plates. The main steps of our algorithm are the following; determination of the Scale and Tilt between CCD and microscope coordinate systems and estimation of signal-to-noise ratio in each field;—image identification and improvement of its position and size;— image final centring;— image selection and storage. Several parameters allow the use of variable criteria for image identification, characterization and selection. Problems related with faint images and crowded fields will be approached by special techniques (morphological filters, histogram properties and fitting models).

GSC+: software for transferring the Guide Star Catalogue on the FK5 system

Abstract Software is developed for selection of star coordinates from the Hubble Space Telescope Guide Star Catalogue (GSC) CD-ROM and for correcting them for three kinds of systematic errors: (1) sky-based errors produced by reference catalogues, (2) plate-based errors produced by telescope optics and by incompleteness of the plate reduction model and (3) plate-based magnitude dependent errors produced by telescope optics and by incompleteness of the plate reduction model. GSC can be used now as a reference catalogue representing the FK5 system on about 0.4 arcsec accuracy level. Further improvement of GSC, including individual plate error correction, is now under development.

Orbit determination and errors of a star catalogue

Abstract We obtain Ceres orbit taking into account all perturbations and applying correction of phase effect to observations. More than 3000 observations have been used and the results agree with other determinations. We have also investigated the influence of systematic errors of a star catalogue on the observations and its effect on final elements. To that aim, a simulation procedure has been applied to Ceres observations, including different laws for errors of star catalogue versus spherical coordinates. The best relations have been applied to real observations of Ceres, in order to obtain elements and star catalogue corrections. Preliminary results of these calculations are presented.

Joint program for automatic analysis of astrographic plates

Pulkovo and Valencia observatories are developing measuring machines based on the “Ascorecord” microscope that allow to undertake automatic measuring programs of different kind of plates (Ortiz et al., 1993). All aspects of astrometry work are covered now by our software: field maps and plate files creation from the PPM and the GSC; precise ephemeris calculation of minor planets and comets, including planetary perturbations; image identification and automatic plate measurement and reduction (Lopez et al., 1994a). For these tasks, correction tables for GSC catalogue vs. PPM, systematic errors (Lopez et al, 1994b) have been obtained. Observing programs using plates and CCD devices at telescope focus are planned (the search of new asteroids and comets, big planets satellites observation, new high density photographic catalogues and some other projects).

Star Image Identification and Characterization on Astrographic Plates

The automatic identification and characterization of star images has great value for the preliminary analysis and measurement of astrographic plates. Our group at Valencia Observatory is using a small 2-D stage and a CCD camera under computer control to perform systematic measurements of bright asteroid plates. We are also applying this method to the processing of astrographic plates with crowded stellar fields and non-stellar objects in collaboration with the Pulkovo Observatory.

Digital Image Processing in the Analysis of Astrometric Plates

In this paper, we display an improvement to our process of semi-automatic measuring of astrometric plates, in which the photometric sensor is substituted by a CCD system of image getting and digitalization. The advantages of this method are analyzed taking into account the possibilities of the image analysis in the space and frequency domain.

Improved Method for Orbital Elements Differential Correction.

As was pointed out by IAU in 1976, an important problem in fundamental astronomy is the improvement of the vernal equinox and equator positions. To this aim, it is necessary to know the accurate values of minor planets orbital elements. The classical methods of orbital elements differential corrections are based on linking the observations at different epochs considering equal derivatives respect to the initial and osculating elements.

Automated astrographic plates measuring process

The astrographic plates measuring process applied at the Astronomical Observatory of Valencia has been described.The measure of astrographic plates of our minor planets observation programme has been carried out by means of a binocular microscope with a photometer, held by a personal computer through an interface. The process of measure in each position of the plate holder is automated, once two stars are selected and the sequence of the objects to be measured is defined.The process will be improved in the next future, by the substitution of the searching device (a photometer) by a CCD camera plus a digitizer board.