IRIS2 Data Reduction - Intro

After the Starlink project came to an end in mid-2005, the Joint Astronomy Center (JAC) in Hawaii, which like the AAO has a large investment in data reduction pipelines built around Starlink infrastructure, took on the role of maintaining the Starlink Software Collection. The JAC released a number of improved versions since 2005, one being "Hikianalia" (link is external), which is available for 64-bit Linux machines, as well as Macs running OS X 10.6 and 10.7.

In 2015, the JAC closed. The software is now maintained by the East Asia Observatory. Since the Hikanalia release, there have been a number of other releases; however, none these have not been thoroughly tested yet.

This version of the Starlink/ORAC-DR software, like its predecessor, includes the _ADD_AUTO_ASTROMETRY_ primitive. Currently, all IRIS2 images are corrected for astrometric distortion (due to the camera optics) before being aligned and combined into a mosaic. The mosaic's World Coordinate System (WCS) which converts pixel coordinates to Right Ascension and Declination has typically only been good to ~5" or so, depending on when and where the telescope pointing was last checked. Both the IRIS2 recipes JITTER_SELF_FLAT and CHOP_SKY_JITTER now call this _ADD_AUTO_ASTROMETRY_ primitive, which uses SExtractor (link is external) to detect objects in the mosaic, downloads 2MASS Point Source Catalogue (link is external) objects from the CDS (link is external) server, then correlates them and applies a new astrometric solution using a 4 coefficient model (link is external) (we thank Brad Cavanagh at JAC for implementing these facilities). However, in addition, this version includes a new recipe which can provide estimates of a number of image statistics e.g. FWHM of point sources, JHKKs photometric zero-points, extinction and sky brightness. This utilises photometry from the 2MASS catalogue and the near-IR broadband colour transformation equations for IRIS2 (Mk2 array) determined by Stuart Ryder (details in the February 2007 AAO Newsletter). For now, these features can only be invoked by using the JITTER_SELF_FLAT_PS recipe.

New-and-improved recipes available

As announced in the February 2005 AAO Newsletter, there have been some recent significant improvements to some of the imaging recipes, as well as the bad pixel masks, in use at the AAT for on-line data reduction. Improvements include cross-talk correction, linearity correction, bad pixel masking, astrometric distortion correction, and pixel over-sampling. 

V2 of these improvements were released on 25 August 2006, and includes automatic selection of an appropriate bad pixel mask, depending on whether the data was taken using the original (Mk1) science-grade array (Mk1: May 2002 - May 2005), the engineering-grade array (Eng: Jun 2005 - April 2006), or the new science-grade array (Mk2: May 2006 onwards).