XMM Users' Handbook

   
OM brightness limit

To avoid damage of the OM photocathode, the maximum allowed source brightness is set to a count rate of $\sim$ 1900 counts/s, corresponding to an m_V= 10 mag A0 star in the V filter. The equivalent brightness limits for the other filters and optical elements are tabulated in Table 19. For calculating the brightness limits an A0 type spectrum was assumed.

 

Table 19: The m_V brightness limits for all OM filters

Filter	Max. m$_{\bf V}$
U	10.8
B	11.6
V	10.0
UVW1	10.0
UVW2	8.9
UVM2	9.2
White	12.7
Magnifier	12.2
Grism 1 (UV)	8.7
Grism 2 (opt.)	9.6

In case an optically bright source beyond these limits is in the OM FOV (not just within an active science window!), users must specify in their proposals that the OM will be in the ``GO-off'' position. It is the user's responsibility to check for the presence of such bright sources. The Guide Star Catalogue (GSC V1.1), which is released as part of SciSim, can be used to check for bright stars. However, it is incomplete at the bright end of the bright end of the magnitude range. Therefore, it is recommended to also check the catalogue USNO-A (V1.0) from the US Naval Observatory (at the URL http://psyche.usno.navy.mil/pmm/).