We present ongoing parallax programs developed at the Bordeaux Observatory several years ago. We describe the necessary steps leading to sub-milliarcsecond accuracy of calculated parallax. We show the importance of global methods for accurate parallax determination.

We present the adaptive optics assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 μas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and — amongst others — will allow the study of motion within a few times the event horizon size of the Galactic Center black hole.

We report on the progress of the Brown Dwarf Kinematics Project (BDKP), which aims to measure the 6D positions and velocities of all known brown dwarfs within 20 pc of the Sun and select sources of scientific interest. In this paper we report on the status of the 33 targets on our parallax list as well as the results of our proper motion survey where we have measured over 400 new proper motions for known late M, L and T dwarfs.

The resolution of pairs of objects closer than the scale of seeing, and of difference of magnitude larger than ten percent is unreliable by direct imaging. The resulting image FWHM differs from a true PSF by no more than four percent. Yet, the peak of the associated Gaussian is shifted to a larger proportion.

The main results are the description of the FWHM and peak location shifts as function of the seeing scale, the centers separation, and of the magnitudes difference. Analytically, the estimators of variation were the resulting Gaussian amplitude, mean value, and standard deviation. The later is shown to be the most reliable estimator.

Interferometry in the near IR aims at providing imaging resolution on the mas scale, and astrometry at the few μas level, from ground based infrastructures using current telescope technology. To take advantage of simultaneous combination of four to eight telescopes, an international consortium is proposing to ESO the development of the VLTI Spectro-Imager. One of the key sub-systems, to measure and correct the atmospheric perturbations relative to the beam phase, is the fringe tracker, aimed at providing the science combiner with long, stable observing conditions. The fringe tracker function in interferometer is equivalent to adaptive optics for conventional telescopes. The fringe tracker concept under study, using minimum redundancy combination and bulk optics, is described.

Tidal vertical variations have been removed in astrometric observations, but the non-tidal ones remain unknown. From the repeated observations of gravimetric networks in China, the non-tidal vertical variations at Beijing-Tangshan and West Yunnan are determined, which are of the order of 0.″2. Astrometric results, including past star catalogs, based on these observations should be corrected.

Sometimes saturated and stretched star images with bad data in their central parts may result in astronomical CCD observations. Considering the special characteristics of the saturated and stretched star images, a method known as MGC(Mean-Geometric-Centering) is put forward for determining the centers of these images. The basic principles and processing pipelines of MGC are introduced, and several noteworthy items in the realization of MGC are discussed. Results of applying MGC to simulated and real data are also presented.

Astronomical Institute of Romanian Academy initiated this project in 2005. The results of researches related to the construction of mechanic systems and the proposed astrometric tasks will be finished in 2008. The module PROTEL is a result of several research groups and it will perform astrometric control observations remotely.

In order to determine precisely positions of the Galilean satellites of Jupiter, it is useful that shortly before and/or after photometric observations of a mutual event, normal CCD imaging observation is also performed for the two small-separation satellites. Experimental observations showed that the two observational types, on the whole, could derive mean (O-C) s with very good internal and external agreement (about 15–20 mas).

The purpose of this work is to do a systematic, deep search for sub-stellar objects orbiting nearby white dwarfs (WDs). The scientific interest spans testing specific predictions of models of common envelope phase, as well as providing constraints to planetary system evolution in advanced stages of its parent star. Additionally, we seek to explore the hypothesis about the origin of metal lines in hydrogen WDs, produced by the accretion of tidal disturbed asteroidal or cometary material. This could be linked to the presence of a planetary object. Here, we show preliminary results of our near-infrared astrometric project.

Long-baseline interferometry with facilities such as the ESO VLTI is beginning to have the capability to measure directly in the range of milliarcsecond and less the angular separation and the angular diameter of some selected eclipsing binary systems. We have begun to carry out such observations with the AMBER instrument. In the special case of double-lined eclipsing binaries with well-detached components, from radial velocity and light curves it is possible to obtain a full solution of all orbital and stellar parameters, with the exception of the effective temperature of one star, which is normally estimated from spectral type or derived from atmospheric analysis of the spectrum or reddening-corrected photometric colors. In particular, we aim at deriving directly the effective temperature at least of one component in the proposed system, thereby avoiding any assumptions in the global solution through the Wilson-Devinney method. We have obtained an independent check of the results of this method concerning the distance to the system. This represents the first step toward a global calibration of eclipsing binaries as distance indicators. Our results will also contribute to the effective temperature scale for hot stars. The extension of this approach to a wider sample of eclipsing binaries could provide an independent method to assess the distance to the LMC.

The reconstruction of the Photographic Zenith Tube (PZT) at Ondřejov has been finished recently. The main improvement of the instrument consists in the replacement of the photographic plate with the CCD chip, and a completely new electronic control system. In addition to the astrometric use of the observations we intend to derive the variations of the local vertical and compare them with gravimetric observations of the nearby station Pecný.

A compiled catalogue consisting of more than 22000 reference stars in the range of 10m – 16m obtained with 235 fields of δ from −17° to +80° around extragalactic radio sources (ERS) selected from the ICRF list. Initial catalogues were obtained from photographic (PG) and CCD observations.

The future PRIMA facility at the Very Large Telescope Interferometer (VLTI) in astrometric mode offers the possibility to perform relative narrow-angle astrometry with 10 micro-arcsecond accuracy. This is achieved with a dual-beam interferometer concept, where a reference star and the scientific target, confined in a 60 arcsecond field, are observed simultaneously. The angular separation of the two stellar objects gives rise to an optical delay in the interferometer, which is measured by the Fringe Sensor Unit (FSU) and an internal laser metrology. PRIMA is using two FSU fringe detectors, each observing the interference of stellar beams coming from one of the two objects and measuring the corresponding phase and group delay. The astrometric observable, yielding the angular separation, is deduced from the group delay difference observed between the two objects. In addition, the FSU phase delay estimate is used as error signal for the fringe stabilisation loop of the VLTI. Both functions of the FSU require high precision fringe phase measurements with a goal of 1 nm rms (corresponding to λ/2000). These can only be achieved by applying a calibration procedure prior to the observing run. We discuss the FSU measurement principle and the applied algorithms. The calibration strategy and the methods used to derive the calibration parameters are presented. Special attention is given to the achieved measurement linearity and repeatability. The quality of the FSU calibration is crucial in order to achieve the ultimate accuracy and to fulfill the primary objective of PRIMA astrometry: the detection and characterisation of extrasolar planetary systems.

TWA 5B is a brown dwarf companion of H=12 mag, 2″ off the ~5 mag brighter triple star CoD-33° 7795 (=TWA 5), a member of the TW Hydrae association of T Tauri stars at ~55 pc. This object is the first brown dwarf around a pre-main-sequence star (confirmed by common proper motion) ever found. In the last year we have newly reduced VLT NaCo data originally taken in 2003 and combined it with all the available astrometric data of the system to investigate possibly detectable orbital motion of the system. Indeed we were able to find linear orbital motion of the system combining data from HST, VLT and Gemini-North.

An original way of application of drift-scan imaging – electronic tracing technique for observation of the fast moving asteroids is presented in this contribution.

The occultation of a 9.1 magnitude star by asteroid (22) Kalliope and its satellite Linus was successfully observed in Japan in 2006 November 7.826 UT. This was the first definite observation of an occultation of a satellite of an asteroid that was discovered previously by other means. As a result the position of the satellite relative to Kalliope was obtained to be d = 0.246 ± 0.011 (arcsec), and P = 313.8 ± 2.7 (deg), where d is the angular distance and P is the position angle. The derived size for Kalliope is (209 ± 40)km × (136 ± 26)km (with the major axis in position angle of (8 ± 17) deg), and that for Linus is (33 ± 3) km. From the observations, the occulted star is also found to be a close double star whose separation is about 0.7 mas in position angle of about 300 deg, and the magnitudes of the components are found to be almost the same (~9.9 mag).

The Exoplanet Search with PRIma (ESPRI) will use the PRIMA dual-feed astrometric capability on the Very Large Telescope Interferometer (VLTI) to perform astrometric detections of extra-solar planets. We present an overview of our data-reduction strategy for achieving 10-μarcsecond accuracy narrow-angle astrometry using the PRIMA instrument. We discuss the error budget for astrometric measurements, and those aspects of our strategy which are designed to minimise the astrometric measurement errors.

On January 26, 2006, an area of the sky of 80 deg2 at α = 9h, δ= 20o (J2000.0) was observed with the 100/120cm Schmidt telescope at the Xuyi station of the Purple Mountain Observatory. Astrometric performance of the telescope is analyzed by this group of CCD observations. The results show that: (1) the CCD images suffer from complicated distortions, and a third order plate model is recommended for reductions; (2) there is no obvious magnitude equation for objects brighter than 16.5 mag, and (3) for this group of CCD images, the astrometric precision for objects brighter than 16.5 mag is better than 70 mas per coordinate when reduced against the UCAC2 catalog.

The main optical instruments of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) are installed separately. Guiding is realized by adjusting the normal direction of the mirror MA. In order to keep the central star imaged on the rotation center of the fiber plug plate, the link between celestial and fiber plug plate coordinate systems has to be established. Some local parameters contain errors so that the normal direction of the MA calculated beforehand may not be accurate enough. The execution error of the telescope also drives the image of the central star to deviate from the rotation center. Therefore, in the process of observations the correction has to be calculated and applied periodically. Here we present the method of calculating the guiding parameters as well as the correction parameters for the LAMOST.