Master creation

Master files are created from raw files with the following purposes:
 

• suppress random noise (by a factor of N^-1/2 where N is the effective number of input files),
• suppress cosmics,
• suppress stellar sources (sky flats, night flats).

IMPORTANT NOTE:   all FORS2 pipeline products do not have the pre-scan regions, which are chopped-off during the reduction process. In order to use the pipeline master calibrations with raw frames, one needs to perform the trimming of input images in the same way. FORS2 post-upgrade CCDs have two overscan regions of 5 pixels each in the X direction (i.e. raws 1-5 and 1030-1034 in the standard 2x2 binning format). The pre-upgrade CCD had two overscans regions of 16 pixels each in the Y direction (i.e. columns 1-16 and 2065-2080 in the standard 1x1 binning).

Find a list of calibration data here.
 
There is a naming convention for pipeline-processed calibration files. Find the list of presently used codes here.

All modes

BIAS frames (MBIA) are measured for all the detector modes (post-upgrade: low/high gain , 2x2/1x1 binning; pre-upgrade: low/high gain, fast/slow readout).

DARK frames are evaluated on occasion to measure the dark current.

Samples of post-upgrade biases for Chip1 and Chip2:
 

file	preview (click to download ps file)	FITS header
master BIAS  (low gain, bin 2x2)		F2_MBIA_020607A_C1lo_2x2.fits F2_MBIA_020607A_C2lo_2x2.fits

 

IMG mode

SCREEN_FLATs (MSFI) can be used to remove high-frequency structure on the detector (fixed-pattern noise with scales between a single pixel and several 10 pixels).

SKY_FLAT (MKFI) frames are measured in evening or morning twilight. These frames typically yield a better large-scale flat-field correction than SCREEN_FLATs. Since they also include high frequency fixed-pattern structure, they are usually taken for flat-fielding science data. Evident from the samples (post-upgrade data) is the "brick wall like" pattern shown by the UV and Blue flat fields. This pattern has its origin in the CCDs thinning procedure.

NIGHT_FLAT (MNFI) frames are generated by the pipeline from jittered SCIENCE images. They are visually checked for remaining sources. Since they require a certain field structure (field not too crowded, no extended sources), they are not routinely available. If available, they provide the best possible illumination correction. Since they ususally have a lower illumination level than SKY_FLATs or SCREEN_FLATs, you should only use smoothed versions of them, and correct for the high spatial frequencies with normalized SKY_FLATs or SCREEN_FLATs.

Samples of post-upgrade data for Chip1 and Chip2:
 

Samples of post-upgrade data for Chip1 and Chip2:
 

file	preview (click to download ps file)	FITS header
master SKY_FLAT_IMG  (U_Special, low gain, bin 2x2)		F2_MKFI_020607A_USp_C1lo_2x2s.fits F2_MKFI_020607A_USp_C2lo_2x2s.fits
master SKY_FLAT_IMG  (B_Bessell, low gain, bin 2x2)		F2_MKFI_020607A_BBE_C1lo_2x2s.fits F2_MKFI_020607A_BBE_C2lo_2x2s.fits
master SKY_FLAT_IMG  (V_Bessel, low gain, bin 2x2)		F2_MKFI_020607A_VBE_C1lo_2x2s.fits F2_MKFI_020607A_VBE_C2lo_2x2s.fits
master SKY_FLAT_IMG  (R_Special, low gain, bin 2x2)		F2_MKFI_020607A_RSp_C1lo_2x2s.fits F2_MKFI_020607A_RSp_C2lo_2x2s.fits
master SKY_FLAT_IMG  (I_Bessel, low gain, bin 2x2)		F2_MKFI_020607A_IBE_C1lo_2x2s.fits F2_MKFI_020607A_IBE_C2lo_2x2s.fits

Photometric Calibration (IMG)

For imaging projects, photometric standards are observed on every clear night through the filters being used that night. Clear nights are defined as nights when no clouds are visible. However, ESO can not certify these nights as photometric.

Pipeline-processed zeropoints are part of the QC1 process. Find zeropoints here.

Reduced STANDARD star files (PSTI) can be used for own extraction and photometric calibration programmes. They are reduced in the same way as SCIENCE files.

ZEROPOINT tables (PZPI) contain extracted fluxes and data for these standard stars. They have been constructed from reduced standard star files using the tool SExtractor for the flux extraction.

file	description	FITS header
zeropoint table  (ALIGNED_PHOTOMETRY_TABLE)  (I_Bessell, low gain, bin 2x2)	table guide	F2_PZPI_020504C_C1lo_2x2s.tfits F2_PZPI_020504C_C2lo_2x2s.tfits
standard star catalogue	table guide	landolt_std_UBVRI.tfits

 

LSS mode

Normalized SCREEN_FLATs (MSFL) contain the high spatial frequencies (fixed-pattern noise, slit transfer function, fringing). They cannot be used to correct for instrument response.

Wavelength dispersion tables (PWDL) contain dispersion solutions for the LSS mode. Find here a description of the dispersion solution recipe.

Samples:

Other modes

The other modes (MXU, MOS) are presently not supported by the pipeline. Only raw calibration data are delivered for Service Mode programmes in these modes.