XMM-Newton Users Handbook

3.5.5.1 OM filter band passes

The OM set of filters covers part of the UV and optical range. The filter throughput curves are displayed in Fig. 87.

Figure 87: Throughput curves for the OM filters, folded with the detector sensitivity.

The plotted quantity is the OM effective area for a given filter including the entire telescope response based on inflight measurements. Aperture radius is 6" for the optical and 17".5 for the UV filter.

The OM effective area has been corrected for time dependent sensitivity degradation. The current (Epoch 2009) throughput is lower: (10, 6, 6, 8, 15, 15) per cent for (V, B, U, UVW1, UVM2, UVW2) filters, respectively.

Zeropoints (by definition the magnitude of an object producing one count per second), have been derived by using, for each filter, the equation:

zeropoint = 2.5 log10(Countrate$_{Vega}$) + m$_{Vega}$.

OM zeropoints have been defined in such a way that Vega has:

B$_{Vega}$ = V$_{Vega}$ = 0.03 mag, U$_{Vega}$ = UVW1$_{Vega}$ = UVM2$_{Vega}$ = UVW2$_{Vega}$ = 0.025 mag.

Zeropoints are listed in Table 19.

An AB magnitude system has been defined also for OM. Their zeropoints are given in Table 19 as well.

Table 19: Zeropoints for various OM filters

Filter	Zeropoint (magnitudes)	AB zeropoint (magnitudes)
V	17.9633	17.9230
B	19.2661	19.0809
U	18.2593	19.1890
UVW1	17.2038	18.5662
UVM2	15.7724	17.4120
UVW2	14.8667	16.5719