• recipe name:FORS_S_GEN_MASTER_BIAS
• input frames: BIAS
• associated templates: FORS1_img_cal_bias

description: Each input frame is bad pixel corrected. Then the master frame is calculated as the mean (AVMODE = 1) or median ( AVMODE = 2) of the stack of input frames. Iteratively each input frame is compared with the master frame for large deviations. If one frame differs too much it is removed from the set of input frames and a new master is produced. As soon as no frame has to be rejected the final master frame has been found. The rejection limits are given by the THRESH parameter.
The median process is modified in that way that instead of the median the mean of all values in an interval centered on the median is taken. A master frame is generated only if MIN_COUNT raw frames are remaining for the averaging process. This ensures a minimum quality of the product.
At the end, the new master frame is compared with the corresponding certified master frame from the calibration database.

• recipe name: FORS_S_GEN_MASTER_DARK
• input frames: DARK
• associated templates: FORS1_img_cal_dark

description: First the individual input frames are corrected for bias and bad pixels, after that the frames are combined to create the (preliminary) master. Both processes are controlled by the keyword AVMODE, which is a two--digit integer. If the first digit is 0, the bias correction is performed by just subtracting a master bias image. If the first digit is 1, the bias correction is performed using the scaled master bias. The scaling is done as follows: Each of the sections of the master bias is divided by its median and multiplied by the median of the corresponding pre-/overscan region of the input frame. If the first digit is 2, the master bias is also scaled, but each of the sections of the master bias is divided by the median of its corresponding pre-/overscan region and multiplied by the median of the pre-/overscan region of the input frame.
The second digit of AVMODE controls the averaging process. If it is 0, the generated master is the average of the means of the input frames and hence constant, if it is 1, the master frame is calculated as the mean, if it is 2 as the median of the stack of input frames.
Iteratively each input frame is compared with the master frame for large deviations. If one frame differs too much it is removed from the set of input frames and a new master is produced. As soon as no frame has to be rejected the final master frame has been found. The rejection limits are given by the THRESH parameter.
The median process is modified in that way that instead of the median the mean of all values in an interval centered on the median is taken. Each input frame is bad pixel corrected in advance.
A master frame is generated only if MIN_COUNT raw frames are remaining for the averaging process. This ensures a minimum quality of the product.
At the end, the new master frame is compared with the certified master frame from the calibration database.

• recipe name:FORS_S_IMG_MASTER_SCRFLAT
• input frames:SCREEN_FLAT_IMG
• associated templates: FORS1_img_cal_scrflat

description: Before the master is generated each screen flat is checked for overexposure. If more than MAXOV percent of the pixels of a frame are overexposed it is not used for the master process.
Then the individual input frames are corrected for bias, dark and bad pixels, after that the frames are combined to create the (preliminary) master. Both processes are controlled by the keyword AVMODE, which is a two--digit integer. If the first digit is 0, the bias correction is performed by just subtracting a master bias image. If the first digit is 1, the bias correction is performed using the scaled master bias. The scaling is done as follows: Each of the sections of the master bias is divided by its median and multiplied by the median of the corresponding pre-/overscan region of the input frame. If the first digit is 2, the master bias is also scaled, but each of the sections of the master bias is divided by the median of its corresponding pre-/overscan region and multiplied by the median of the pre-/overscan region of the input frame.
Iteratively each input frame is compared with the master frame for large deviations. If one frame differs too much it is removed from the set of input frames and a new master is produced. As soon as no frame has to be rejected the final master frame has been found. The rejection limits are given by the THRESH parameter.
The median process is modified in that way that instead of the median the mean of all values in an interval centered on the median is taken. Each input frame is bad pixel corrected in advance.
A master frame is generated only if MIN_COUNT raw frames are remaining for the averaging process. This ensures a minimum quality of the product.
At the end, the new master frame is compared with the corresponding certified master frame from the calibration database.

• recipe name: FORS_S_IMG_MASTER_SKYFLAT
• input frames: SKY_FLAT_IMG
• associated templates: FORS1_img_cal_skyflat

purpose: Creates a master twilight flat from a set of twilightflat images.

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: Before the master is generated each twilight flat is checked for overexposure. If more than MAXOV percent of the pixels of a frame are overexposed it is not used for the master process.
Then the individual input frames are corrected for bias, dark and bad pixels, after that the frames are combined to create the (preliminary) master. Both processes are controlled by the keyword AVMODE, which is a two--digit integer. If the first digit is 0, the bias correction is performed by just subtracting a master bias image. If the first digit is 1, the bias correction is performed using the scaled master bias. The scaling is done as follows: Each of the sections of the master bias is divided by its median and multiplied by the median of the corresponding pre-/overscan region of the input frame. If the first digit is 2, the master bias is also scaled, but each of the sections of the master bias is divided by the median of its corresponding pre-/overscan region and multiplied by the median of the pre-/overscan region of the input frame.
Iteratively each input frame is compared with the master frame for large deviations. If one frame differs too much it is removed from the set of input frames and a new master is produced. As soon as no frame has to be rejected the final master frame has been found. The rejection limits are given by the THRESH parameter.
The median process is modified in that way that instead of the median the mean of all values in an interval centered on the median is taken. Each input frame is bad pixel corrected in advance.
A master frame is generated only if MIN_COUNTraw frames are remaining for the averaging process. This ensures a minimum quality of the product.
At the end, the new master frame is compared with the corresponding certified master frame from the calibration database.

• recipe: FORS_S_IMG_STDSTAR
• input frames: STANDARD_IMG
• associated templates: FORS1_img_obs_crstd, FORS1_img_obs_std

purpose: Do a standard reduction of the input frame (debias, flatfielding), search for objects, determine their luminosities and align the derived photometry table with a standard star reference catalog.

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 incoming standard star frame is searched for overexposed pixels. Some basic statistical parameters are determined. Then the standard star frame goes through a standard reduction procedure, i.e.\ bad pixel, bias and dark correction as well as flatfielding. All these operations are done in case an appropriate calibration frame is present in the set of reference frames. If SCALE=NO, the bias correction is performed by just subtracting a master bias image. If SCALE=MED, the bias correction is performed using the scaled master bias. The scaling is done as follows: Each of the sections of the master bias is divided by its median and multiplied by the median of the corresponding pre-/overscan region of the input frame. If SCALE=OVE, the master bias is also scaled, but each of the sections of the master bias is divided by the median of its corresponding pre-/overscan region and multiplied by the median of the pre-/overscan region of the input frame. Alternatively to the master bias and master dark images constant values ( BIAS_CONS , DARK_CONS ) may be subtracted.
The luminosities of the objects on the image are now determined and stored in a photometry table (see recipe FORS_IMG_OBS_PHOTOMETRYfor details). This table is aligned with a standard star reference catalog. The parameter POINTACC defines the search radius for the catalog search. Only objects within a radius POINTACC around a catalog position are potential matches. If there is more than one coincidence for a catalog object the catalog magnitude is compared with the measured values and the best match is used. Object magnitudes are estimated by means of an already existing extinction coefficients table if there is any, otherwise are computed using default extinction coefficients.

• 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), search for objects, determine their luminosities and correct for extinction.

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 incoming science frame is searched for overexposed pixels and some basic statistical parameters are determined. Then the science frame goes through a standard reduction procedure, i.e. bad pixel, bias and dark correction as well as flatfielding. All these operations are done in case an appropriate calibration frame is present in the set of reference frames. If SCALE=NO, the bias correction is performed by just subtracting a master bias image. If SCALE=MED , the bias correction is performed using the scaled master bias. The scaling is done as follows: Each of the sections of the master bias is divided by its median and multiplied by the median of the corresponding pre-/overscan region of the input frame. If SCALE=OVE , the master bias is also scaled, but each of the sections of the master bias is divided by the median of its corresponding pre-/overscan region and multiplied by the median of the pre-/overscan region of the input frame. Alternatively to the master bias and master dark images constant values ( BIAS_CONS , DARK_CONS ) may be used.

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

description: Before the master is generated each night sky flat is checked for overexposure. If more than MAXOV percent of the pixels of a frame are overexposed it is not used for the master process.
Then the individual input frames are corrected for bias, dark and bad pixels, after that the frames are combined to create the (preliminary) master. Both processes are controlled by the keyword AVMODE, which is a two--digit integer. If the first digit is 0, the bias correction is performed by just subtracting a master bias image. If the first digit is 1, the bias correction is performed using the scaled master bias. The scaling is done as follows: Each of the sections of the master bias is divided by its median and multiplied by the median of the corresponding pre-/overscan region of the input frame. If the first digit is 2, the master bias is also scaled, but each of the sections of the master bias is divided by the median of its corresponding pre-/overscan region and multiplied by the median of the pre-/overscan region of the input frame.
Iteratively each input frame is compared with the master frame for large deviations. If one frame differs too much it is removed from the set of input frames and a new master is produced. As soon as no frame has to be rejected the final master frame has been found. The rejection limits are given by the THRESH parameter.
The median process is modified in that way that instead of the median the mean of all values in an interval centered on the median is taken. Each input frame is bad pixel corrected in advance.
A master frame is generated only if MIN_COUNT raw frames are remaining for the averaging process. This ensures a minimum quality of the product. At the end, the new master frame is compared with the corresponding certified master frame from the calibration database.