T. Pauwels

The daily processing of asteroid observations by Gaia

Abstract The Gaia mission started its regular observing program in the summer of 2014, and since then it is regularly obtaining observations of asteroids. This paper draws the outline of the data processing for Solar System objects, and in particular on the daily “short-term” processing, from the on-board data acquisition to the ground-based processing. We illustrate the tools developed to compute predictions of asteroid observations, we discuss the procedures implemented by the daily processing, and we illustrate some tests and validations of the processing of the asteroid observations. Our findings are overall consistent with the expectations concerning the performances of Gaia and the effectiveness of the developed software for data reduction.

Gaia Data Release 2: Observations of solar system objects

Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. Aims. We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. Methods. To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). Results. The overall astrometric performance is close to the expectations, with an optimal range of brightness G ∼ 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G ∼ 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.

The RUSTICCA project

Abstract In this paper we present the RUSTICCA-project, consisting of upgrading the Uccle Schmidt-Telescope by installing a CCD-camera. We describe the technical characteristics, the observing programmes, and discuss the advantages and disadvantages of the configuration.

Optimizing asteroid orbit computation for Gaia with normal points

Context. In addition to the systematic observations of known solar-system objects (SSOs), a continuous processing of new discoveries requiring fast responses is implemented as the short-term proces ...

Astrometric reductions of ESO-Schmidt plates

Abstract We have performed a series of astrometric reductions of ESO-Schmidt plates. In this paper we compare the results of reductions with linear transformation formulae with the results of reductions with the full third degree transformation formulae. We find that there are only small differences between both reductions, provided that an equidistant projection is used between the sky and the tangential plane rather than the usual gnomonic projection, and that enough reference stars are used. These small differences are almost entirely due to the larger errors in the third-degree reduction, showing the superiority of linear transformation formulae over third degree formulae for ESO-Schmidt plates. Reductions using only stars from a certain magnitude class show that there is no measurable magnitude effect. And finally, comparing reductions using only one single plate with reductions using the mean measurements of seven plates show that taking the mean of seven plates does improve the positions.

Astrometric reductions of ESO-Schmidt platesfn1fn2

Abstract We have performed a series of astrometric reductions of ESO-Schmidt plates. In this paper we compare the results of reductions with linear transformation formulae with the results of reductions with the full third degree transformation formulae. We find that there are only small differences between both reductions, provided that an equidistant projection is used between the sky and the tangential plane rather than the usual gnomonic projection, and that enough reference stars are used. These small differences are almost entirely due to the larger errors in the third-degree reduction, showing the superiority of linear transformation formulae over third degree formulae for ESO-Schmidt plates. Reductions using only stars from a certain magnitude class show that there is no measurable magnitude effect. And finally, comparing reductions using only one single plate with reductions using the mean measurements of seven plates show that taking the mean of seven plates does improve the positions.

Astrometric reductions of ESO-Schmidt plates fn1 fn1Based on plates taken at the Schmidt-telescope of the European Southern Observatory, La Silla, Chile. fn2 fn2Based on measurements performed at the mama measuring machine. mama (Machine Automatique à Mesurer pour LAstronomie) is developed and operated by cnrs\insu (Institut National des Sciences de lUnivers).

Abstract We have performed a series of astrometric reductions of ESO-Schmidt plates. In this paper we compare the results of reductions with linear transformation formulae with the results of reductions with the full third degree transformation formulae. We find that there are only small differences between both reductions, provided that an equidistant projection is used between the sky and the tangential plane rather than the usual gnomonic projection, and that enough reference stars are used. These small differences are almost entirely due to the larger errors in the third-degree reduction, showing the superiority of linear transformation formulae over third degree formulae for ESO-Schmidt plates. Reductions using only stars from a certain magnitude class show that there is no measurable magnitude effect. And finally, comparing reductions using only one single plate with reductions using the mean measurements of seven plates show that taking the mean of seven plates does improve the positions.