next previous
Up: Extragalactic database

2. General features

In the following sections, each parameter will be designated in a unique way by the word used in the LEDA query language. The correspondence between this designation and the meaning is given in Appendix B together with the variable name used in programs and the format (FORTRAN convention). Such a designation aims at avoiding subscript or exponant characters which can not be used in simple text printing or keyboard entering.

The error on each parameter is now calculated using a method which gives better description of the actual accuracy of the measurement. In previous catalogs the standard error on an average parameter was simply calculated from the sum of weights of each individual parameter (the weight being the inverse square of individual standard error). Now, the standard error is augmented quadratically, by the external standard deviation between each parameter. This estimate will be designated as the actual uncertainty. The precise expression is explained in Appendix A. The main advantage of this new definition is that a parameter with low actual uncertainty cannot result from discrepant individual measurements. So, this definition allows the user to select undoubtly good data.

All parameters are available through LEDAgif or from a CD-ROM distributed by the Observatoire de Lyon via the CNRS.

Copyright by the European Southern Observatory (ESO)