SWIFT: Technical Specifications

The Oxford SWIFT spectrograph is an image-slicer based integral field spectrograph, that is coupled with the PALAO adaptive optics system on the Hale 200-inch telescope. The instrument comprises of a pre-optics, image slicer, and identical twin spectrographs, each consisting of a collimator, VPH grating, camera and an LBNL thick, fully depleted, 4k x 2k CCD array detector. There is also an internal calibration unit, with spectral calibration and flat fielding lamps.


Expected sensitivity

The following input parameters have been used to estimate the expected line and continuum sensitivity of the instrument. An exposure time calculator will shortly be available for detailed sensitivity calculations. In the meantime, expected performance can be scaled using the two examples provided below.


Operationally, we expect individual exposure times to be restricted to 1800 secs due to the number of cosmic ray events. As the LBNL chips have a thick (250 μm) silicon substrate, we are much more sensitive to cosmic ray events. Longer exposures will be made up of 1800 secs sub-units. If allowed by the source size, the rectangular field of view can be used to nod-on-IFU so that all the exposure time is spent observing the object.

Overheads: Apart from the overheads involved in achieving AO loop closure on the desired target, there should be only a few minute additional overhead for target acquisition and positioning within the field of view. SWIFT will provide an almost instantaneous reconstructed image to help with the acquisition. Detector read-out time is ≈ 40 seconds. SWIFT is equipped with a shutter to control short exposure times. The only configurable part in the instrument is the choice of spaxel scale, changes to which will need less than half a minute.