Observing Constraints and Classification Rules
General Observing Constraints
Every requested observation has multiple observing constraints. Typical observing constraints are:
- the allowable brightest lunar phase
- the allowable smallest moon-to-object angular separation
- the allowable maximum airmass
- the allowable maximum image size (i.e. FWHM at observed wavelength, 'seeing')
- the allowable sky transparency
- for Adaptive Optics instruments (currently CRIRES, NACO and SINFONI), the Strehl ratio on the reference star.
- for instruments observing in mid-IR (CRIRES and VISIR), the allowable maximum Precipitable Water Vapour (PWV)
- the allowable absolute time window (i.e. for time critical events, multi-epoch monitoring)
- the allowable local sidereal time range (i.e. for ADI observation)
- for VLTI instruments, the availability of the desired baseline
The Observing Constraints are specified by the user at Phase 2 for each Observation Block. Since the execution conditions required by each programme are an important ingredient in the process of building up the Long Term Schedule of an observing semester, and thus determines which programmes can or cannot be scheduled, users are not allowed to specify at Phase 2 constraints that are more strict than those specified in the original proposal. Users can however relax the constraints during the submission of their Phase 2 material. The values in the OB constraint sets that are selected (and approved) during Phase 2 preparation (and review) cannot be changed later during the observing period.
General Classification Rules
Quality Control of OBs executed in Service Mode will be based on the user's specified constraints for airmass, atmospheric transparency, seeing (i.e. image quality), moon constraints, as well as Strehl ratio for Adaptive Optics mode observations.
Note: the seeing constraint as defined in the OB is judged against the full width at half maximum (FWHM) of a point source in the resulting image (or spectral image), i.e. at the observed wavelength, for most of the VLT instruments (i.e. it is the image quality).
Additional Observing Constraints and Classification Rules for KMOS
The final additional rules for KMOS will be presented here in June/July 2013.
The image quality (seeing constraint) is measured on the reconstructed IFU images of the reference stars in either the acquisition or the science exposures.
Do not overspecify the Moon constraints! The Moon does not directly affect infrared observations, but it does affect the quality of the active optics corrections, in particular if the reference stars are too faint. It is recommended not to observe objects when they are closer than 30 degrees from the Moon. For KMOS, the Moon illumination (FLI) can be entirely relaxed in most cases by selecting FLI=1.