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XMM-Newton Science Analysis System


omsrclistcomb (omsrclistcomb-2.7.1) [xmmsas_20070708_1801-7.1.0]

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Standard (Johnson) Magnitudes and Colours

Standard magnitudes can only be computed for the U, B and V filters and hence the only standard colours that can be calculated are U-B, B-V and U-V. An important point to note, is that these standard colours can be computed using the following instrumental colours - U-B, B-V, U-V, (UVW1-U), (UVW1-B), (UVW1-V), (UVW2-B) and (UVW2-V). Omsrclistcomb computes all possible standard magnitudes for each of the U, B and V filters and displays them in separate columns.

The program loops through these colours and if the relevant instrumental magnitudes are present computes the standard magnitudes and standard colour. Since it is possible that a particular source may have a standard magnitude computed twice for the same filter (eg standard B from U-B and B-V), the program will add, if necessary, a column for each of these standard magnitudes. These values should, of course, be identical to within the errors, but discrepancies may arise due to a number of reasons (eg an inaccurate instrumental magnitude).