XMM-Newton Users Handbook

3.5.3 OM optical elements

The OM is equipped with a filter wheel holding several optical elements that can be moved into the light path. These elements, which are described here, comprise not only lenticular filters, but also two grisms. The complete set of optical elements is collected in Table 16. Their arrangement on the OM filter wheel is indicated by the position number on the filter wheel. Sequences of exposures using different optical elements must always have increasing filter wheel position numbers. Observations with the three UV broad-band filters UVW1, UVW2, and UVM2, for example, must always be conducted in the order UVW1, UVM2, UVW2 (positions 7, 8 and 9).

From AO-16 (announced in 2016) it is possible for programmes with specific approval by OTAC to perform several turns of the filter wheel. In other words it is possible to perform series of exposures in which a sequence of filters (ordered in increasing filter wheel position numbers) is repeated several times.

Table 16: OM optical elements
Filter wheel position number Filter name
0 Blocked
1 V
3 U
4 B
5 White
6 Grism 2 (visible)
7 UVW1
8 UVM2
9 UVW2
10 Grism 1 (UV)

European Space Agency - XMM-Newton Science Operations Centre