On the use of the Hipparcos intermediate astrometricdata

2008

The current status of astrometry in Astro-WISE is explored. This includes the underlying mechanisms, procedures, performance, and accuracies of both the local and the global astrometric solution, as well as the improvement from the local to the global solution. Using all currently Astro-WISE processed data from the WFI instrument on the MPG/ESO 2.2m telescope (24512 frames, more than 3000 exposures), we show that the overall accuracies are consistent with and due to the precision of the USNO-A2.0 reference catalog (0.3 arcsec RMS and 1 arcsec systematic) for the local solution and are approximately 0.04 arcsec for the global solution. In addition, it is found that the precision of the underlying software (SExtractor, LDAC, SWarp) in extracting sources, applying solutions, and regridding frames to 0.200 arcsec per pixel is of the order 0.02 arcsec RMS. The performance of the local solution has a virtually 100% success rate with respect to the underlying software, a 98.0% success rate...

2003

Orbital solutions for binary or multiple stellar systems that combine astrometry (e.g., position angles and angular separations) with spectroscopy (radial velocities) have important advantages over astrometric-only or spectroscopic-only solutions. In many cases they allow the determination of the absolute masses of the components, as well as the distance. Yet, these kinds of combined solutions that use different types of observations in a global least-squares fit are still not very common in the literature. An outline of the procedure is presented, along with examples to illustrate the sort of results that can be obtained. The same method can easily be extended to include other types of measurements (times of eclipse, Hipparcos observations, interferometric visibilities and closure phases, parallaxes, lunar occultations, etc.), which often complement each other and strengthen the solution.

Astrometric Techniques, 1986

The acquisition, preparation and distribution of machine-readable astrometric data by the Astronomical Data Center (ADC) are described. Examples of certain general changes in data structure and format to im prove compatability with other computers and software processing sys tems and to increase storage efficiency are discussed, as are the pres ent data archive and request history of the ADC. Current development work in the areas of astrometric and positional catalogs is described.

Highlights of Astronomy, 1992

The methods developed to predict instrumental magnitudes, to monitor the ageing of the optics, to calibrate photometrically the payload and finally to build up a high accuracy photometric reference system are tested against space observations. The quality of ephemerides for long period variables are also discussed.

The Hipparcos mission (1989-1993) resulted in the first space-based stellar catalogue including measurements of positions, parallaxes and annual proper motions accurate to about one milli-arcsecond. More space astrometry missions will follow in the near future. The ultra-small Japanese mission Nano-JASMINE (launch in late 2013) will determine positions and annual proper motions with some milli-arcsecond accuracy. In mid 2013 the next-generation ESA mission Gaia will deliver some tens of micro-arcsecond accurate astrometric parameters. Until the final Gaia catalogue is published in early 2020 the best way of improving proper motion values is the combination of positions from different missions separated by long time intervals. Rather than comparing positions from separately reduced catalogues, we propose an optimal method to combine the information from the different data sets by making a joint astrometric solution. This allows to obtain good results even when each data set alone is ...

Highlights of Astronomy, 1986

The Hipparcos star mapper will be used to determine magnitudes in two colours and the positions for about 500 000 stars. The typical accuracy for the mean values is about 0.03 mag and 0.03 arcsec respectively for a star of B = 11.0 mag and B-V =0.7 mag. The photometric system and part of the data analysis are outlined.

Astronomical Data Analysis Software and Systems Xvi, 2007

We describe the Astrometric Data Reduction Software (ADRS) for the Phase Referenced Imaging and Micro-Arcsecond Astrometry (PRIMA) instrument, which is being developed by the PRIMA Astrometry Operations and Software (PAOS) Consortium in collaboration with ESO. PRIMA will be commissioned at the VLTI in 2007/2008. The primary objective of the astrometry program with this instrument will be the detection of extra-solar planets and the characterization of their orbits. The goal is to achieve a relative astrometric accuracy of the order of 10 micro-arcseconds. In order to reach this accuracy the ADRS has to analyze all available PRIMA data uniformly and consistently. We describe in this paper how this will be done and what ESO infrastructure requirements must be fulfilled.

Astronomy & Astrophysics, 2014

Context. The first release of astrometric data from Gaia is expected in 2016. It will contain the mean stellar positions and magnitudes from the first year of observations. For more than 100 000 stars in common with the Hipparcos Catalogue it will be possible to compute very accurate proper motions due to the time difference of about 24 years between the two missions. This Hundred Thousand Proper Motions (htpm) project is planned to be part of the first release. Aims. Our aim is to investigate how early Gaia data can be optimally combined with information from the Hipparcos Catalogue in order to provide the most accurate and reliable results for htpm. Methods. The Astrometric Global Iterative Solution (agis) was developed to compute the astrometric core solution based on the Gaia observations and will be used for all releases of astrometric data from Gaia. We adapt agis to process Hipparcos data in addition to Gaia observations, and use simulations to verify and study the joint solution method. Results. For the htpm stars we predict proper motion accuracies between 14 and 134 µas yr −1 , depending on stellar magnitude and amount of Gaia data available. Perspective effects will be important for a significant number of htpm stars, and in order to treat these effects accurately we introduce a formalism called smok (scaled model of kinematics). We define a goodness-of-fit statistic which is sensitive to deviations from uniform space motion, caused for example by binaries with periods of 10-50 years.

Astronomy and Astrophysics Supplement Series, 2000

Only 235 entries were processed as astrometric binaries with orbits in the Hipparcos and Tycho Catalogue (ESA 1997). However, the Intermediate Astrometric Data (IAD) and Transit Data (TD) made available by ESA make it possible to re-process the stars that turned out to be spectroscopic binaries after the completion of the Catalogue. This paper illustrates how TD and IAD may be used in conjunction with the orbital parameters of spectroscopic binaries to derive astrometric parameters. The five astrometric and four orbital parameters (not already known from the spectroscopic orbit) are derived by minimizing an objective function (χ 2 ) with an algorithm of global optimization. This code has been applied to 81 systems for which spectroscopic orbits became available recently and that belong to various families of chemically-peculiar red giants (namely, dwarf barium stars, strong and mild barium stars, CH stars, and Tc-poor S stars). Among these 81 systems, 23 yield reliable astrometric orbits. These 23 systems make it possible to evaluate on real data the so-called 'cosmic error' described by , namely the fact that an unrecognized orbital motion introduces a systematic error on the proper motion. Comparison of the proper motion from the Hipparcos catalogue with that re-derived in the present work indicates that the former are indeed far off the present value for binaries with periods in the range 3 to ∼ 8 years. Hipparcos parallaxes of unrecognized spectroscopic binaries turn out to be reliable, except for systems with periods close to 1 year, as expected. Finally, we show that, even when a complete orbital revolution was observed by Hipparcos, the inclination is unfortunately seldom precise.

Space astrometry now permits accurate determinations of stellar radial motion, without using spectroscopy. Using Hipparcos data, this is possible for stars in nearby moving clusters, where all stars share nearly the same space velocity. A maximumlikelihood method has been developed to yield kinematic cluster parameters (including the internal velocity dispersion) purely from parallaxes and proper motions. The deduced astrometric radial velocities of the Ursa Major open cluster and the Hyades have inaccuracies of 0.3 and 0.4 km s ?1 , respectively, and the internal cluster velocity dispersions are found to be 0:66 0:10 and 0:25 0:04 km s ?1 (consistent with random stellar motions). Remaining errors arise from uncertainties in excluding binary stars. The errors get worse for the more distant Coma Berenices cluster. The tting of cluster parameters includes all individual stellar distances. The constraint of a uniform average cluster velocity markedly improves the parallax precisions (roughly by a factor two), compared with Hipparcos data for individual stars. The HR diagram for the Hyades now reveals a very narrow main sequence line (not band), even suggesting some wiggles in it. Discrepancies between astrometric and spectroscopic radial velocities reveal e ects (other than stellar motion) that a ect wavelength positions of spectral lines. Such are caused by stellar pulsation, surface convection, and by gravitational redshifts. A parallel programme is obtaining and analysing high-precision spectroscopic radial velocities for di erent classes of spectral lines in these programme stars.