Calibration data for FORS1 are taken for two purposes:

• assess the instrument status
• reduce science data

Generally, FORS1 calibration data are taken as daytime calibrations. On user request, also nighttime calibrations can be obtained as part of the Observing Block which generates the SCIENCE data ("attached calibrations").

The calibration data taken obtained in the supported modes are processed by QC Garching to obtain calibration solutions. These solutions come as:

• calibration product FITS file frames (e.g. master BIAS or FLATFIELD frames)
• calibration product FITS tables (e.g. wavelength dispersion tables, photometric tables)

All 4-port frames belonging to pipeline-supported modes are processed using FTU  (Fits Translation Utility) and a set of IRAF/IDL readable keywords is added to the the FITS headers. In particular a full description of the port structure, including pre-scan regions, is included.

IMPORTANT NOTE:   all FORS1 pipeline products do not have the pre-scan regions which are chopped-off during the reduction process. As a consequence, master calibrations/reduced science files start at X pixel coordinates @17 and stop at @2064. In order to use the pipeline master calibrations with raw frames, one needs to perform the trimming of input images in the same way.

RAW CALIBRATION DATA

The following types of raw calibration data exist for the supported modes:

IMAGING

Frame Type	DPR Type	DPR Tech	Purpose
BIAS	BIAS	IMAGE	bias level, RON
DARK	DARK	IMAGE	dark current
SKY FLAT	FLAT,SKY	IMAGE	flat field of science data
SCREEN FLAT	FLAT,LAMP	IMAGE	gain, bad pixel map, lamp efficiency, fixed pattern noise
IMG STD	STD	IMAGE	photometric zeropoints, extinction and colour coefficients

LSS

Frame Type	DPR Type	DPR Tech	Purpose
BIAS	BIAS	IMAGE	bias level, RON
SCREEN FLAT	FLAT,LAMP	SPECTRUM	flat field of science data, slit transfer function
SPEC LAMP	WAVE,LAMP	SPECTRUM	2D dispersion solution
SPEC STD	STD	SPECTRUM	spectrophotometric calibration

MOS

Frame Type	DPR Type	DPR Tech	Purpose
BIAS	BIAS	IMAGE	bias level, RON
SCREEN FLAT	FLAT,LAMP	MOS	flat field of science data, slit transfer function
SPEC LAMP	WAVE,LAMP	MOS	2D dispersion solution
SPEC STD	STD	MOS	spectrophotometric calibration

MASTER CALIBRATION DATA AND PRODUCTS

The following types of master calibration data are produced for the supported modes:

IMAGING

Frame Type	Recipe	Description	N	Products
BIAS	fors_s_gen_master_bias	create a MASTER BIAS from set of N input raw frames	5	MASTER BIAS
DARK	fors_s_gen_master_dark	create a MASTER DARK from set of N input raw frames	5	MASTER DARK
SKY FLAT	fors_s_img_master_skyflat	create a MASTER SKY FLAT from set of N input raw frames	3-5	MASTER SKY FLAT
SCREEN FLAT	fors_s_img_master_scrflat	create a MASTER SCREEN FLAT from set of N input raw frames	2	MASTER SCREEN FLAT BAD PIXEL MAP
NIGHT FLAT	fors_s_img_master_nightflat	create a MASTER NIGHT FLAT from set of N input raw frames	4-10	MASTER NIGHT FLAT
IMG STD	fors_s_img_stdstar	reduce STANDARD STAR IMAGES and obtain photometric ZEROPOINT of the night	1	REDUCED IMAGE ZEROPOINT TABLE

LSS

Frame Type	Recipe	Description	N	Products
BIAS	fors_s_gen_master_bias	create a MASTER BIAS from set of N input raw frames	5	MASTER BIAS
SCREEN FLAT	fors_s_lss_normflat	create a MASTER SCREEN FLAT from set of N input raw frames	2	MASTER SCREEN FLAT
SPEC LAMP	fors_s_lss_wave	compute DISPERSION SOLUTION	2	MASTER SPEC LAMP WAVELENGHT DISPERSION TABLE

MOS

Frame Type	Recipe	Description	N	Products
BIAS	fors_s_gen_master_bias	create a MASTER BIAS from set of N input raw frames	5	MASTER BIAS
SCREEN FLAT	fors_s_mos_normflat	create a MASTER SCREEN FLAT from set of N input raw frames	2	MASTER SCREEN FLAT
SPEC LAMP	fors_s_mos_wave	compute DISPERSION SOLUTION	2	MASTER SPEC LAMP WAVELENGHT DISPERSION TABLE

ASSOCIATION RULES

The creation of calibration product follows well-defined association rules.

CALIBRATION CASCADE

Like for all astronomical data, the reduction of FORS1 calibration frames requires a cascading scheme where the mutual dependencies of products and raw frames have to be respected. Master Biases can be produced from raw files only, but all the other products require the prior generation of other calibration products. The proper sequence of all these production steps is called the calibration cascade.

NAMING SCHEME

After production and certification, the calibration products are renamed after a scheme which includes type, creation date and relevant FORS1 settings.