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Image Mode

Image Mode

GHRS Instrument Handbook


The GHRS is, of course, primarily a spectrograph, but it includes useful imaging capabilities, especially because the detectors of the GHRS are blind to much of the visible light that dominates the flux of most stars. You may wish to request an IMAGE, for example, to confirm that the telescope had your object properly centered in the data-taking aperture before the exposure was taken.

Note the following in using the imaging capability:

Image Mode Parameters

The GHRS as a Slitless Spectrograph

In IMAGE mode you may specify a grating instead of a mirror as the spectrum element (note that this may not be done in Acquisition Mode). Doing so for a target that emits primarily in lines can yield the equivalent of using a slitless spectrograph over a very small portion of the sky (the 1.74 arcsec square region of the LSA). Thus the focus diodes would be swept over the image of the line to produce a picture that is resolved spatially in the y direction and spectroscopically in the x direction. This mode of use would be very slow if all you wanted was the spatial structure of a small object (the FOC would probably be better), but there might be interesting uses for obtaining spectrophotometrically pure, spatially resolved images in the ultraviolet. Please consult us if you wish to explore this option.

Image Mode Parameters
The GHRS as a Slitless Spectrograph