Calibration Plan

Standard Calibrations

The most commonly used observing configurations of each instrument are calibrated by means of the Observatory's Calibration Plan. Calibration Plans for each instrument and mode are described in detail in their corresponding User Manual, and their execution times are not charged to the Service Mode programmes.

Additional Calibrations

Please check carefully in the User Manual whether or not the instrument configurations that you plan to use are included in the instrument's Calibration Plan. If this is not the case, you must provide additional OBs for calibration appropriate for each mode not included in the Calibration Plan. Their execution time is then charged to your time allocation.

User-supplied OBs for calibration are only executed once. You should assume that your science OBs will be executed completely independently of each other, possibly on different nights, and take into account that no user-supplied OB (for a science or a calibration target) will be executed more than once. You should submit enough OBs to cover that situation. For example, if you need to observe and flux-calibrate six targets in a filter that is not supported by the calibration plan of the instrument, you need to provide six OBs for photometric calibration to allow for the case in which each target is observed on a different night. This must be done even if the same calibration star can be used for all the science targets.

Please indicate in the User Comments fields of science OBs when a user-provided calibration must be executed contiguously.

'Concatenation containers' should be used within p2 to link science and calibration observations that must be executed contiguously.

Please note that there are two separate kinds of calibrations in operational terms:

  • Calibrations that observe a reference celestial source, like a spectrophotometric standard star or a nearly-featureless star for the measurement of telluric lines. The OBs prepared for this kind of calibration are generically considered as normal OBs (to be prepared within an "OB" in p2), and their construction is the same as for other science OBs. However, depending of the instrument they use either templates whose name contains the indicator calib, or flags in the templates that indicate that the observation is intended for calibration.
  • Calibrations with no celestial source associated, like flat fields taken with a flat field lamp or dark exposures. OBs for this kind of calibration should be prepared within the "CB" (Calibration Block) in p2, as no acquisition template needs to be specified in this case. Calibrations to be executed in daytime are the most common examples in this category.

FORS Calibration Plan

The FORS calibration plan can be found in the FORS User Manual.

Standard Star OBs

The FORS User Manual outlines which standard star exposures are supported by the FORS Calibration Plan. If that is sufficient for your calibration goals, no special calibration OBs need to be submitted.

For programs requiring photometric conditions it is advisable to submit a standard field OB to be executed close in time to the science OB, to confirm the stability of the extinction coefficients. This standard field MUST be observable no matter whether the science OB is observed at the beginning or the end of the night.

The list of recommended standard fields is given at:

If no such standard field can be identified, the user can submit an OB with empty coordinates, and the Observatory will take care of finding a suitable field. In that case the exposure times can be set to 3 seconds for BVR, and 1 second for I.

Calibration OBs

In case you need (special) calibrations beyond those for the standard configurations as outlined in the FORS Calibration Plan (e.g. after a successful waiver request) special calibration OBs need to be submitted. However, such lamp calibrations should never be attached to science OBs to be executed during nighttime. It is not possible to obtain calibration lamp exposures during the night. Only daytime lamp calibrations will be taken. The level of accuracy achievable with such calibrations is described in the FORS User Manual.

All FORS calibration OBs must begin with the template FORS2_img_cal_coll and end with the respective templates to obtain flat field and arc exposures:

  1. FORS2_img_cal_coll
  2. FORS2_MODE_cal_scrflat(_fast)
  3. FORS2_MODE_cal_wave(_fast)

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