• recipe name: FORS_S_IMG_SCIENCE
• input frames:SCIENCE_IMG
• associated templates: FORS1_img_obs_crsplit, FORS1_img_obs_exp,FORS1_img_occ_crsplit, FORS1_img_occ_exp

purpose: Do a standard reduction of the input frame (debias, flatfielding) and search for objects.

warning: The twilight images of FORS1, which are used to create master sky flats, show evidence for a feature, whose position depends on the rotator angle (see overview). This limits the achievable photometric accuracy to about 5%. For more information please look at the FORS Secondary Standard and Absolute Photometry Project.

description: The bias master calibration is subtracted. Cosmic rays are detected and removed from image (by interpolation of surrounding pixels). The debiased signal is then divided by the normalised sky flat field, and the overscan regions, if present, are removed from the result. The reduced image is finally sent to a source detection and extraction application (SExtractor 2.5.0). The data are not normalized to 1 second exposure time.

This recipe is also used to reduce preimaging exposures (made for the preparation of spectroscopic observations).

products (for naming rules see here):

• reduced science image (SIMG), debiased and flat-fielded science image (including errors in the second extension of this frame)
• photometric background image (SPBI), as derived and used by SExtractor
• source table (SSRI), which contains all sources detected by SExtractor and some of the SExtractor flags
• object table (SOTI), which contains all "good" sources detected by SExtractor