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The XMM-Newton Optical Monitor
The Optical/UV Monitor Telescope (XMM-OM) is mounted on the mirror support platform of XMM-Newton alongside the X-ray mirror modules. It provides coverage between 170 nm and 650 nm of the central 17 arc minute square region of the X-ray field of view, permitting routine multiwavelength observations of XMM targets simultaneously in the X-ray and ultraviolet/optical bands.
The XMM-OM consists of a Telescope Module and a separate Digital Electronics Module, of which there are two identical units for redundancy. The Telescope Module contains the telescope optics and detectors, the detector processing electronics and power supply. There are two distinct detector chains, again for redundancy. The Digital Electronics Module houses the Instrument Control Unit, which handles communications with the spacecraft and commanding of the instrument, and the Data Processing Unit, which pre-processes the data from the instrument before it is telemetered to the ground.
The Telescope Module consists of a modified 30 cm Ritchey-Chretien telescope with a focal ratio of f/12.7, i.e. a focal length of ca. 3.8 m. The incoming light is reflected by a mirror inclined at an angle of 45° to one of two redundant detectors. The OM telescope tube is ca. 2 m long. Incoming light falls onto the primary mirror, which reflects it onto the secondary, from where it goes to the inclined mirror that reflects it onto the detector. A filter wheel is mounted immediately in front of the detectors . This does not only contain filters, but also other optical elements, like grisms and a magnifier (i.e. optics for a longer focal length and thus higher resolution on the sky).
OM Main Characteristics
A schematic of the Optical Monitor
Click below for more details on the components of Optical Monitor.
The XMM Optical Monitor was built by a consortium of institutes from the UK, the USA and Belgium, led by the PI group at the Department of Space and Climate Physics at the Mullard Space Science Laboratory, part of University College London.
K.O. Mason et al. 2001, A&A 365, L36