SCUBA2_CHECK_CAL

Perform SCUBA-2 calibration checks on standard sources

Description:

Calculate fluxes, FCFs and beam size from a given uncalibrated map of a point source. The results are written to a log file called log.checkcal if desired.

Procedure:

• The images are cropped to the given size (as specified in the FITS headers or via the MAP_HEIGHT and MAP_WIDTH recipe parameters, whihc must be at least twice the diameter of the aperture).

• A background may be fitted and removed. (Optional - only if the REMOVE_BACKGROUND recipe parameter is true.)

• The beam size is determined using KAPPA beamfit.

• FCFs are calculated from the cropped (background-subtracted) image.

• The source flux and its uncertainty are derived from aperture photometry on these images. The background is estimate from an annulus with inner and outer radii of 1.25 and 2.0 times the aperture radius.

• The map is calibrated using either the standard FCF or the one derived above (if the USEFCF recipe parameter is true).

• The noise is calculated from the calibrated map.

• The matched filter is applied to the calibrated map.

• Results are written to a log file, log.checkcal.

By default this recipe only works on known calibration sources. However, the user may specify the source flux at 850 and/or 450 um by using recipe parameters called FLUX_850 and FLUX_450 respectively. The fluxes for different sources may be specified by appending the target name (in upper case with spaces removed), e.g. FLUX_850.HLTAU. (See also CALC_SCUBA2_FCF.)

By default a log file is written containing a variety of information about the data and the values calculated.

Notes:

• The input data must be uncalibrated in order to calculate an FCF from calibrator observations. (The PICARD recipe UNCALIBRATE_SCUBA2_DATA can be used to undo the default calibration.)

• The default behaviour is to leave every file created during the recipe on disk. This may not be desirable - see the KEEPFILES recipe parameter below to reduce the number of output files.

• Re-processing data already processed by this recipe is not recommended.

• If the recipe parameter FITSURFACE_KEEPSURFACE is true, then a file will be created (for each input file) with suffix _surface.

• Documentation for other recipes may list other recipe parameters that appear to be applicable to some of the steps in this recipe, but are not shown due to the possibility of adverse interactions.

• The fits for beam size and FCF calculation are independent and are not guaranteed to use the same parameters. The FIT_GAUSSIAN recipe parameter may be used to enforce a gaussian or non-gaussian fit. By default, a two-component gaussian will be fitted for known calibrators with a signal-to-noise ratio of at least 100. If the signal-to-noise is less than 100, the beam fit will fall back to a single gaussian while the FCF fit will be a single component with an unconstrained radial falloff parameter.

Available Parameters :

The following parameters can be set via the -recpars option:
Radius of aperture in arcsec for calculating total flux. The default is 30 arcsec.
BACKGROUND_FITMETHOD
Method to use for removing background. May be fitsurface, findback, plane or dc. Default is fitsurface.
FINDBACK_BOX
Size of the box (in pixels) used by findback. Default is 11.
FIT_GAUSSIAN
Flag to indicate whether or not to force a Gaussian fit to the source when estimating the beam parameters. Default is 1 (fit Gaussian).
FIT_FIXAMP
A flag to denote that the amplitude of the fit to the source should be fixed as the peak value in the map. Default is 0 (amplitude is a free parameter).
FIT_FIXBACK
Specifies the background level to be used in the fit to the source. May be ! to allow the background to float. If not given, the default is either a fixed level of 0 for known calibrators, or the background is left as a free parameter.
FITSURFACE_FITPAR
Up to two values which define either the order of the polynomial (for polynomial) or the number of knots (for spline) in the X and Y directions respectively. A single number means the same value is used for both axes. Default is 2 for polynomial, 4 for spline.
FITSURFACE_FITTYPE
Type of fit to use with fitsurface. May be polynomial or spline. Default is polynomial.
FITSURFACE_KEEPSURFACE
A flag to denote whether or not to keep the fitted surface on disk. Useful for debugging purposes. Default is 0 (do not keep on disk).
FLUX_450
Source flux density at 450 um in Jy. Source-specific values may be given by dot-appending the source name in upper case with spaces removed. For example, FLUX_450.DGTAU.
FLUX_850
Source flux density at 850 um in Jy. Source-specific values may be given by dot-appending the source name in upper case with spaces removed (see above).
KEEPFILES
A flag to indicate whether or not to keep all files produced by the recipe. May be 0 to keep no files, or $+$1 to keep only files with suffix _crop, _back and _mf. Default is -1 (keep all files).
LOGFILE
Flag to denote whether to write results to a log file at the end of processing. Default is 1 (write log file).
MAP_HEIGHT
Height of map in arcsec after cropping. Must be at least twice the aperture diameter. Default is that in the FITS header.
Radius in arcsec of the circular region to define the map. Must be at least twice the aperture radius. Overrides the use of MAP_HEIGHT and MAP_WIDTH.
MAP_WIDTH
Width of map in arcsec after cropping. Must be at least twice the aperture diameter. Default is that in the FITS header.
Flag to denote whether to mask the source before removing the background. Default is 0 (do not mask the source).
NOISE_METHOD
Method used to calculate the noise in the calibrated image. May be VARIANCE to use the variance, MASK to mask out the source and calculate the image-plane standard deviation, or MINIMUM to determine the lowest standard deviation in a series of apertures placed on the image. Default is VARIANCE, and minimum match is supported.
PSF_MATCHFILTER
Name of a file to use as the PSF when applying the matched filter.
REMOVE_BACKGROUND
A flag to indicate whether or not a background should be estimated and removed from the image. Default is 0 (do not remove a background).
USEFCF
Flag to denote whether to calibrate the data using the FCFs derived in this recipe (1) or use standard FCFs (0). Standard FCFs will be used if not specified.
USEFCF_CALTYPE
Calibration type to use if USEFCF is 1. May be ARCSEC, BEAM or BEAMMATCH. Default is BEAM.

None.

Logfile Format

The log file contains the following entries: 1. Input filename 2. UT date (YYYY-MM-DDTHH:MM:SS.S) 3. Object name 4. Observation number 5. Wavelength (um) 6. Airmass 7. 225-GHz tau 8. tau at observing wavelength 9. Aperture radius (arcsec) 10. USEFCF flag 11. Flux within an aperture (pW) 12. Uncertainty in derived flux above (pW) 13. Noise derived from variance (mJy/beam) 14. Flux conversion factor derived using the integrated flux within an aperture (Jy/sq arcsec/pW) 15. Uncertainty in above FCF 16. Flux conversion factor derived from peak of Gaussian fit to source (Jy/beam/pW) 17. Uncertainty in above FCF 18. Flux conversion factor derived from peak of Gaussian fit to source after processing with a matched filter (Jy/beam/pW) 19. Uncertainty in above FCF 20. FWHM of main beam (arcsec) 21. Contribution of error beam (per cent) 22. Flag to indicate whether the beam fit was a Gaussian