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calibration SW-arm imaging

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SW-arm Imaging Dark (Hawaii detector)

The dark recipe generates one single product:

product name (initial tag) PRO.CATG key of product header contents
IS_MDRK MASTER_DARK average dark frame


[dark.gif  11K]
Master dark frames of the Hawaii array in DoubleCorr read mode.

Purpose. Dark frames are measured to monitor the overall performance and status of the Hawaii array.

Recipe. The pipeline input stack consists of three raw frames coherent in the detector setup (meaning the same read mode and discrete integration time = DIT). The recipe generates the master dark frame and calculates several quality control parameters, like the dark current and the read out noise per detector quadrant.


SW-arm Twilight Flat

The twilight recipe, as is operated, generates three products:

product name (initial tag) PRO.CATG key of product header contents
IS_MIFL MASTER_IMG_FLAT Master twilight flat
IS_MERR MASTER_IMG_FLAT_ERRMAP error map from the linear fit
IS_MBPX MASTER_BPM bad pixel map; non-linear features

[sitf.gif 14K] Master twilight flat frame showing the gain map (the array pixel to pixel gain variation) and two small size areas in the upper right quadrant with light obscuration.

Purpose. The master twilight flats show the relative sensitivity (the gain) of the array pixels. Twilight flats are observed in sequence of about 15-20 frames during dawn or dusk. The bad pixel map indicates pixels with obscuration due to dust particles in the optical path.

Recipe. The twilight flat recipe offers several methods. Among these the following is used: A master imaging dark is subtracted from the twilight raw frames and the gain map is produced using a proportional relation (gain =a*flux) per pixel. The normalized 'a' factors build the master twilight flat, the error map product shows the deviations from the proportional relation for the fit gain map and a bad pixel map shows strong outliers.

SW-arm Photometric Zeropoint

The photometric zeropoint recipe generates two products:

product name (initial tag) PRO.CATG key of product header contents
IS_PIZP ZPOINT verification image with 8 subframes
IS_PIZT ZP_TAB log of the most important calculation steps


[order.gif 4K
Pipeline product showing the raw difference frames of a sequence of 5 jittered standard star exposures.

Purpose. Photometric standard stars are observed in four filters J, Js, Ks, and H whenever possible, preferably in clear and photometric nights at low air mass. The photometric zeropoint is a conversion factor between the flux rate (e.g. ADU/sec) and the magnitude.

Recipe. The five raw input frames are flat fielded and are subtracted from each other for reasons of sky elemination. In total 8 difference frames are build out of the five raw input frames. The frames are subtracted in a certain manner and each difference frame is evaluated individually. The order of the eight difference frames is: frame #2 minus frame #1, frame #3 minus frame #1, frame #4 minus frame #2, frame #5 minus frame #3, frame #6 minus frame #4, frame #7 minus frame #5, frame #8 minus frame #7. For the aperture photometry the target radius is 30 pixel (=4.4 arcsec) and the background is determined from a ring with 40 < r < 60 pixel (or 5.9 < r < 8.9 arcsec), using a image scale of 0.148 arcsec/pixel. The recipe provides the min-max-rejected median of the 8 measured instrumental magnitudes (corrected for extinction and color-terms) in the table product.

Here is an example of a ZP_TAB FITS binary table product :

# file IS_PZPT_070913A_SW_H.fits
# extensions 1
# --------------------------------------------
# Number of columns 8
510.433| 531.202| 24.712| 262671| 2340.48| -1.46387| 4.2948| 13.0299
814.65| 837.031| 24.7842| 280754| 2155.04| 1.93127| 2.39434| 4.14245
814.639| 837.006| 24.764| 275574| 2141.51| -5.72107| 2.39047| 4.26757
204.701| 836.47| 24.7165| 263768| 2151.81| 5.04639| 4.58733| 1.96287
204.708| 836.474| 24.7184| 264225| 2123.12| -11.6448| 4.61417| 2.31847
205.023| 225.989| 24.7115| 262558| 2538.58| 12.6671| -1| 6.20834
205.007| 225.963| 24.7028| 260455| 2526.15| -1.62207| -1| 6.21728
815.074| 227.306| 24.7557| 273469| 2300.58| 2.41565| 2.86547| 5.23474


The columns describe: the position of the source in pixel (POSX, POSY), the photometric zeropoint, the integral (FLUX), the peak counts in ADU (PEAK), th residual backgorund in ADU (BGD), the FWHM along x (FWHMX) and the y-axis (FWHMY). In the example given above, no FWHMY could be derived from two of the eight sky subtracted frames.

SW-arm Illumination

The illumination correction recipe generates two products:

product name (initial tag) PRO.CATG key of product header contents
IS_PILL ILLUM_FRAME polynomial fit frame
IS_PILX ILLUM_FLUX log of the most important calculation steps

[wave.gif 10K]

17 standard star images with a fixed jitter offset summed up. The standard star is used to trace the distribution of the instrument efficiency. In the given example, the first of the 17 standard star images is located in the center of the detector and is not marked.





[wave.gif 10K]

2d polynomial fit to the distribution of the relative instrument efficiency.




Example ILLUM_FLUX product table:

# file IS_PILX_070501A_LW_H.fits
# extensions 1
# --------------------------------------------
# Number of columns 3
510| 532| 49135
126| 148| 52075.7
382| 150| 51288.7
637| 150| 53533.3
893| 149| 54963
891| 405| 51450
637| 405| 53486.3
383| 405| 28121
127| 405| 49560
127| 659| 49852
382| 659| 51748.3
637| 659| 53688
892| 659| 51763.7
893| 916| 49578
637| 914| 63160
382| 914| 62355.7
126| 915| 49287

Purpose: The illumination template takes images of a photometric standard distributed as a regular grid over the detector. The flux of the standard star images is used to derive the large scale efficiency distribution of the instrument.

Recipe: The illumination recipe takes 17 input images.The recipe fits a 2d polynomial to the regular grid of standard star fluxes.

Note: Illumination frames are used for technical purposes within the ESO VLT data flow . For this reason no flat field correction is applied to avoid a bias introduced by large scale structures intrinsic to the twilight sky. Illumination correction frames can be used for enhanced science data reduction. Please read the note on the illumination QC web page.

SW-arm detector linearity

The detector linearity recipe and data reduction for the Hawaii array is identical to that used for the Aladdin array. See data reduction of the LW-arm for details.