quircinfo -- Reduction scripts for Hokupa'a/QUIRC data
The QUIRC package contains tasks for processing Hokupa'a/QUIRC data obtained at Gemini North. The specifics of the individual tasks can be found in their help files. This document describes the common features of the tasks and gives a description of the Hokupa'a/QUIRC data format.
The tasks are designed to provide a fast nearly "hands-off" reduction as well as the flexibility to optimize the hidden parameters to achieve the best possible results.
The tasks produce logfiles of the performed processing steps. The name of the logfile may be set in each individual task, or at the package level by setting quirc.logfile.
The tasks add header keywords to the output images. These header keywords contain information about the performed processing steps and the values of the critical parameters for the tasks that were used.
All data from Hokupa'a/QUIRC are simple FITS images. The QUIRC package is designed to process the images as simple FITS. It is recommended to use imtype="fits". This is set automatically when loading the GEMINI package.
- QFLAT - Derive flat field and bad pixel mask for QUIRC
QFLAT is used for deriving normalized flat fields as well as bad pixel masks for the Hokupa'a/QUIRC data. The input images are dome flat fields (or GCAL flat fields) and darks. The output images are the normalized flat field and a bad pixel mask. The user can choose to produce both output images or only one of these.
- QFASTSKY - Derive sky image for QUIRC, median or min/max filtering
QFASTSKY is used for determination of sky images by median or min/max filtering. There is made no attempt to specifically flag objects in the sky images. The task is mostly used for QuickLook reductions at the telescope.
- QSKY - Derive sky image for QUIRC, includes flagging of objects
QSKY is used for determination of sky images. Objects in the input images are flagged using information about the FWHM of the PSF and the signal in the objects. It is recommended to use QSKY rather than QFASTSKY for science quality reductions.
- QREDUCE - Reduce images from QUIRC (sky, flat)
QREDUCE is used for sky subtraction and flat field correction of the science data.
For typical reductions the user will need appropriate flat fields and dark images, on-target science images and sky images. If the target is not extended and the field is uncrowded the on-target images may be used in place of the sky images. This assumes that sufficiently large dither steps were used during the observations.
1. Use QFLAT to derive normalized flat fields and a bad pixel mask.
2. Use QSKY (or alternatively QFASTSKY) to derive sky images. The near-IR sky level and structure varies during the night, and care should be taken to combine only sky images that are close enough in time to each other and to the relevant science images that such variations are non-significant. This may take some experimentation.
3. Use QREDUCE to subtract the sky images and apply the flat fields. Each filter should be processed separately, as QREDUCE takes only one sky image at the time as its input.
The processed images may be co-added with the task GEMTOOLS.IMCOADD.
Photometry may be derived with any suitable photometry package. It should be noted that images from Adaptive Optics systems have PSFs with very large wings. The PSF for Hokupa'a/QUIRC images varies slightly over the field of view. This variation is more noticeable the further adaptive optics guide star was from the observed field. Photometry packages like DAOPHOT should be used with caution.
The tasks in the QUIRC package are designed to operate on simple FITS images. The tasks will not work on multi-extension FITS files. The tasks should be used with imtype="fits". It cannot be guaranteed that all the tasks work as expected if imtype is set to any other image type.
qflat, qfastsky, qsky, qreduce