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.

Since P90 'concatenation containers' can be used within P2PP version 3 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 P2PP3), 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 P2PP, 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.

VIMOS Calibration Plan

Night calibrations

Nighttime calibrations consisting of 1 arc and 3 flat field exposures are still mandatory for a MOS observations with the grisms HR_blue, MR and HR_orange. It is not any longer mandatory for a MOS observations with the grisms LR_red, HR_red and LR_blue. The wavelength calibration accuracies of daytime calibrations for the different grisms are summarized in this memo by Wolff et al. (2014).

Night calibrations (arcs and flats) are mandatory for all IFU OBs, i.e. the VIMOS_ifu_cal_NightCalib template should be attached as the last template to all IFU OBs.

Standard Star OBs

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

Pre-imaging users are requested to indicate in the Readme file whether they need a photometric standard taken in the same night as the pre-imaging observations.

Calibration of blue wavelength for grisms HR_orange and HR_blue

For the wavelength calibration of the HR_orange grism below 5800 Angstroem there are only two very weak arc lines available. Therefore, the wavelength calibration in that part is very unreliable or even impossible. ESO is working on a solution to solve this problem.

When using the HR_blue grism in IFU mode the dome flatfields have not enough flux below 4000 Angstroem to calibrate the data properly (tracing of spectrum positions). In case you need that wavelength region for your science case it is recommended to ask for extra twilight flatfields, which have enough flux in the blue wavelength regime.




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