Astrometry in the GAIA-era
In the framework of long-term dynamical studies, the old observations have appeared necessary for the modeling of transient events, or for observable periodic behavior. Thus, the first objective of the NAROO project is to achieve a new astrometric reduction of old observations (astro-photographic plates and CCDs) using the last release of the Gaia-DR reference star catalog to ensure the best measurement accuracy.
The figure below shows the positioning accuracy of Gaia reference stars. An important result: the stars available on the oldest plates, typically one century-old, will have an astrometric precision of 1 mas, allowing the same reduction as for current observations. Moreover, all observations will now be expressed in the same reference frame.
GAIA positioning accuracy - Credits F. Mignard.
Interest for a new analysis and reduction
The figure below shows the interest of a new reduction of old observations. The figure provides a comparison between two reductions: the one made by D. Pascu (1994), and the one made by V. Robert et al. (2016) after digitization. The RMS vs ΔV magnitude plots show the decreasing trend of the decline in satellite positioning accuracy. The new analysis led to an improvement of the accuracy.
Comparison of satellite positioning accuracy (V. Robert et al. 2016).
Asteroids and comets
Old observations of asteroids and comets had a very poor astrometric accuracy because of the inaccurate reference star catalogs used at that time. A new astrometric reduction after digitization is very useful to express all data in the same reference frame, and with the same accuracy. The main goals are:
- Analysis of Schmidt plates containing a large number of objects still unknown.
- Pre-discoveries of TNOs, comets and Near Earth objects NEAs/NEOs.
- Increasing the time span of the observations made and used in the theoretical models to detect and quantify the non-gravitational and/or cumulative effects.
A Schmidt plate may contain thousands objects with a lot of small bodies of the Solar System.