Validation

I have been a Gaia CU8 validation manager since 2014 and have been in charge of verifying CU8 science products. CU8 (Coordination Unit 8) is one of the nine CUs in Data Processing and Analysis Consortium (DPAC) and is responsible for classifying sources and estimating astrophysical parameters. See GAIA-C8-TN-MPIA-DWK-007 for details about the validation processes.

[ Figure 1. Diagram of validation processes ]

During Gaia operations, CU8 Apsis software (Bailer-Jones+ 2013) will produce outputs including source classification (e.g. stars, galaxies, QSOs) and astrophysical parameters (e.g. temperatures, extinctions, etc). In order to assess these outputs, it is necessary to examine them in various ways such as plotting figures, calculating statistical quantities, etc., which is referred to as the internal validation. In addition there should be an external validation, which compares the Apsis results with other published results on the same objects.

Figure 1 summarizes the validation processes. The basic idea is that each module developer (or manager) produces a table listing the Gaia sources he/she would like to obtain outputs in order to validate his/her module. These data are then written to a dedicated table during the Apsis chain run. These output tables can then be downloaded by the developer and (manually) examined/compared with external catalogue.

[ Figure 2. Example of validation plot ]

Module developers should examine the output tables by calculating statistics and/or plotting various figures. Figure 2 is one example of such validation figures showing a histogram of estimated astrophysical parameters.