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Context. We study large trans-Neptunian objects (TNOs) using stellar occultations. Aims. We derive precise astrometric predictions for stellar occultations by Eris, Haumea, Ixion, Makemake, Orcus, Quaoar, Sedna, Varuna, 2002 TX300, and 2003 AZ84 for 2011-2015. We construct local astrometric catalogs of stars complete to magnitudes as faint as R = 18-19 in the UCAC2 (Second US Naval Observatory CCD Astrograph Catalog) frame covering the sky path of these objects. Methods. During 2007-2009, we carried out an observational program at the ESO2p2/WFI (2.2 m Max-Planck ESO telescope with the Wide Field Imager) instrument. The observations covered the sky path of the selected targets from 2008 to 2015. We performed the astrometry of 316 GB images using the Platform for Reduction of Astronomical Images Automatically (PRAIA). With the help of field distortion patterns derived for the WFI mosaic of CCDs, we reduced the overlapping mosaics of CCDs. Results. We derive positions in the UCAC2 frame with 40 mas precision for stars up to the catalog magnitude completeness limit (about R = 19). New stellar proper motions are also determined with 2MASS (Two Micron All Sky Survey) and the USNO B1.0 (United States Naval Observatory B 1.0) catalog positions as a first epoch. Astrometric catalogs with proper motions were produced for each TNO, containing more than 5.35 million stars covering the sky paths with 30' width in declination. The magnitude completeness is about R = 19 with a limit of about R = 21. We predicted 2717 stellar occultation candidates for all targets. Ephemeris offsets with about from 50 mas to 100 mas precision were applied to each TNO orbit to improve the predictions. They were obtained during 2007-2010 from a parallel observational campaign carried out with telescopes from 0.6 m to 2.2 m in size. Conclusions. This extends our previous work for the Pluto system to large TNOs, using the same observational and astrometric procedures. The obtained astrometric catalogs are useful for follow-up programs at small to large telescopes used to improve the candidate star positions and TNO ephemeris. They also furnish valuable photometric information for the field stars. For each TNO, updates on the ephemeris offsets and candidate star positions (geometric conditions of predictions and finding charts) are made available by the group at http://www.lesia.obspm.fr/perso/bruno-sicardy/. [ABSTRACT FROM AUTHOR]

Gaia photometric capabilities should distinguish quasars to a high degree of certainty. With this, they should also be able to deliver a clean sample of quasars with a negligible trace of stellar contaminants. However, a purely photometric sample could miss a non negligible percentage of ICRF sources counterparts - and this interface is required to align with the ICRS and de-rotate the GCRF (Gaia Celestial Reference Frame), on grounds of continuity. To prepare a minimum clean sample forming the initial quasar catalogue for the Gaia mission, an all sky ensemble was formed containing 128,257 candidates. Among them there is at least one redshift determination for 98.75%, and at least one magnitude determination for 99.20% of the targets. The sources were collected from different optical and radio lists. We analyze the redshift, magnitude, and color distributions, their relationships, as well as their degree of completeness.Complementary, the candidate sources enable to form an optical representation of the ICRS from first principles, namely, kinematically non-rotating with respect to the ensemble of distant extragalactic objects, aligned to the mean equator and dynamical equinox of J2000, and realized by a list of adopted coordinates of extragalactic sources. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

Quasars are the choicest objects to define a quasi-inertial reference frame. At the same time, they are active galactic nuclei powered by a massive black hole. As the astrometric precision of ground-based optical observations approaches the limit set by the forthcoming GAIA mission, astrometric stability can be investigated. Though the optical emission from the core region usually exceeds the other components by a factor of a hundred, the variability of those components must surely imply some measure of variability of the astrometric baricenter. Whether this is confirmed or not, it puts important constraints on the relationship of the quasar's central engine to the surrounding distribution of matter. To investigate the correlation between long-term optical variability and what is dubbed as the “random walk” of the astrometric center, a program is being pursued at the WFI/ESO 2.2m. The sample was selected from quasars known to undergo large-amplitude and long-term optical variations (Smith et al. 1993; Teerikorpi 2000). The observations are typically made every two months. The treatment is differential, comparing the quasar position and brightness against a sample of selected stars for which the average relative distances and magnitudes remain constant. The provisional results for four objects bring strong support to the hypothesis of a relationship between astrometric and photometric variability. A full account is provided by Andrei et al. (2009). [ABSTRACT FROM PUBLISHER]

We present a Véron & Véron based optical extragalactic reference frame progress report. [ABSTRACT FROM PUBLISHER]