A New Generic Way to Define Astrometric Calibration for Gaia Data Processing

摘要

Gaia is ESA's ambitious space astrometry mission with a foreseen launch date in early 2012. Its main objective is to perform a stellar census of the 1000 Million brightest objects in our galaxy (completeness to V=20 mag) from which an astrometric catalog of micro-arcsec level accuracy will be constructed. A key element in this endeavor is the Astrometric Global Iterative Solution (AGIS) -the mathematical and numerical framework for combining the ti 70 available observations per star obtained during Gaia's 5yr lifetime into a single global astrometric solution. The fundamental working principles of AGIS was shown (04.1) at last year's ADASS XVIII. This time we present a new generic astrometric calibration scheme recently implemented in AGIS. For the development of the data processing software, the traditional astrometric calibration scheme is a heavy task as each new change in the model produces changes in the code, a need for new simulation data, new validations tests, etc. The new scheme allows the calibration of the astrometric instrument to be specified in a more generic and flexible manner. The entire model is defined with an external configuration file that can be modified at any time with no or only minimal impacts on the software. The implementation results in acceptable run time overheads compared to the direct approach with a fixed hard-coded calibration model. This new approach can be a starting point to convert other fixed and hard coded scheme into this more analytical breakdown solution.