UIST data

UIST is a general-purpose imager and spectrometer operating in the 1-5 $\mu$m range at UKIRT, It was commissioned in 2002 October, replacing all spectroscopy functions of CGS4 except for echelle spectroscopy, all imaging functions of IRCAM/TUFTI and all imaging functions of UFTI except the Fabry-Perot filter. It also includes a deployable image slicing IFU mounted in the slit wheel. Slicing mirrors are used to reformat a $6.0\times3.3$-arcsec region of the sky into fourteen slices (the IFU contains eighteen slicing mirrors but four are currently not usable), each fifty pixels long, offset from one another along their length. This produces a staggered column on slitlets (as shown in the figure) which is used as the input for the spectrometer in place of the long slit.

Figure: The UIST staggered slitlets.

Data acquisition, reduction and control software is provided by the JAC ORAC system. The data-reduction part of the system, ORAC-DR, is provided by JAC and distributed by Starlink, and consists of a fully automated perl-based pipelining software sitting on top of the Starlink software collection. A general introduction to the ORAC-DR system can be found in SUN/230. The data-reduction recipes are documented in SUN/246 and at the JAC web site. An arc spectrum (Ar or Kr from the UIST calibration unit) is used to straighten the staggered slitlets (which correspond to a wavelength displacement from one slice to another) and apply a wavelength calibration to the image. The individual slice images will then be copied to form $y$-$\lambda$ planes of an $x$,$y$,$\lambda$ data cube. Recipes are also provided to carry out tasks such as flat-fielding and flux-calibration. Many of the recipes have specific requirements in terms of, for instance, darks and flats fields which must be acquired before a target observation is obtained and reduced on-line.